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Saturday mornings are a good time to grab a cup of coffee, tune tWCCO.jpghe radio to WCCO 830AM, and listen U of M Extension answer listeners' questions about everything from aphids to zinnias, from grapes to grasshoppers. Heck, we just like talking about Minnesota gardening!

Saturdays, 8-9am on WCCO radio, 830 on the AM dial. year-round
Host: Denny Long
U of M Extension Smart Garden team: Julie Weisenhorn, Sam Bauer, Mary Meyer
Extension Master Gardener volunteers: Theresa Rooney (Hennepin County), Darren Lochner (Hennepin County)
Listen for special guests like Jeff Hahn, John Loegering, Karl Foord ....!
Podcasts of previous shows here: WCCO Smart Gardens

Starting seeds = Spring

Tomato seedlings 041414.jpg

Planting seeds is a sure sign of Spring. Luckily here in Horticultural Science, there is no lack of seed starting happening. My Master Gardener friends, who work on campus, and I started seeds for the 2014 annual seed trials in the greenhouses. The trials are in their 32nd year (I think) and this year, over 100 people are participating by planting and growing out the seeds in their home garden, school gardens, community gardens, and demonstration gardens. On campus, our seed trials can be found in the Department's Display and Trial Garden located at the corner of Gortner and Folwell Avenues on the U of MN St. Paul campus. Trials this year include six herbs for tea, and six varieties of container tomatoes, bull horn peppers, spinach, yellow squash, carrots, shasta daisy, and alyssum. Seed trial results are published each year in the spring issue of Northern Gardener magazine.

I also started some seeds for the Gopher Adventures garden. GA is a day camp for kids here at the U. Kids ages 5-13 can choose to do all sorts of activities at the U from computers to rock climbing to art and dance to - yep - gardening. Master Gardeners and I plant a children's garden on the west end of the display garden. Edible plants, flowers, trees, monarch way station, plants for pollinators - even a miniature garden called "Little Goldy's Garden" complete with a very small golden gopher (it's a magnet on a stick). Last year we had straw bale gardens and pallet gardens. The seeds I started for GA are in my office on a heat mat under a grow light. I used a tray with fifty Earth plugs from Seeds of Change. I used my own seeds from home and planted a couple kinds of peppers, nasturtiums, Salvia, Echnicaea, basil, teddy bear sunflowers, and even a mystery seed that will hopefully emerge (and I can identify). This year, we'll be planting Smart Snacks - an Arboretum educational program about plants that are good snacks for people and pollinators.

Seeds are amazing. Everything needed to grow a plant (water and soil not withstanding) are encapsulated in a seed. Everyone should plant a few seeds and feel a little amazed at the result!

Minnesota Gardening Calendar 2014

Karl Foord - Extension Educator, Horticulture

There is still time to get the 2014 Minnesota Gardening Calendar.

This year's calendar has two inserts:

The first is PLANTS FOR MINNESOTA BEES produced by Elaine Evans who is a member of the Bee Lab (

The second is a poster celebrating the release of the native little bluestem (Schizachyrium scoparium) cultivar Blue Heaven™ by Dr. Mary Meyer. One side of the poster contains information on USING NATIVE GRASSES IN THE LANDSCAPE. The feature article for the calendar provides additional information on this subject.

This year's calendar also has a new category of GARDENING TIPS called KIDS' CORNER. These are tips on projects you can do with the younger people in your life to teach them about gardening and nature. These tips were created by Robin Trott.

Karl Foord

Photo 1: Dawn Redwood (Metasequoia glyptostroboides)

Sometimes we include photos that reach beyond our present time. The picture for January is of a dawn redwood (Metasequoia glyptostroboides). This is the caption.

Dawn redwood, a deciduous conifer, was thought to be extinct until rediscovered in 1944. It is today maintained as a ornamental hardy to zone 5. Look for its close relative (M. occidentalis) in the form of large petrified trunks and stumps in the badlands of western North Dakota.

If you are in that vicinity look them up. You will not be disappointed.

The University of Minnesota Bookstore is managing sales of the Minnesota Gardening Calendar. This link will take you to their website.

We hope you will enjoy this calendar as much as we enjoy creating it for you!

Something "bugging" you????? Join Julie Weisenhorn and special guest extension entomologist, P1150490.JPGJeff Hahn, this Saturday, 8-9am, on WCCO Radio's "Smart Gardens" (830 AM on the dial). This is your opportunity to get Jeff's help in solving those pesky pest questions. Listeners can call or text in questions for Jeff and Julie.

About the show: WCCO Radio has teamed up with U of M Extension to bring you "Smart Gardens" which airs every Saturday from 8-9 a.m. If you have something to say, call-in at 651-989-9226 or text 81807. For more info and podcasts: WCCO Smart Gardens

Karl Foord - Extension Educator, Horticulture

Click on the link to see the video with host Dr. Mary Meyer, Professor of Horticulture

Rhubarb (Rheum rhabarbarum)

Karl Foord

Photo 1: Rhubarb (Rheum rhabarbarum)

Chives (Allium schoenoprasum)

Karl Foord

Photo 2: Chives (Allium schoenoprasum)

Common Thyme (Thymus vulgaris)

Karl Foord

Photo 3: Common Thyme (Thymus vulgaris)

Horseradish (Armoracia rusticana)

Flowering Plant Video Library

Karl Foord - Extension Educator, Horticulture

This is the beginning of a flowering plant video library. The goal of this library is to give a short, guided, visual, one to two minute introduction to flowering plants that thrive under Minnesota conditions. You will be able to see the plant in a natural or landscape setting and see how it might fit into your landscape.

We will begin with three early flowering bulbs Snowdrops, Striped Squill, and Siberian Squill. The library will continue to grow and we hope that you will find video to be an enjoyable way to learn about and experience flowering plants.

Striped squill (Puschkinia scilloides var. libanotica)

Snowdrops (Galanthus nivalis)

Siberian Squill (Scilla siberica)

A Look at the New USDA Hardiness Zone Map

A hardiness zone map (HZM) provides information that gardeners and professional horticulturalists use in determining which herbaceous and woody perennial plants will survive cold temperature in a particular geographic area. Last week the United States Department of Agriculture released a new hardiness zone map to replace the older 1990 version.

As with past maps, the new map:
  • is a visual representation of average annual minimum temperatures across the United States. Data points used to create the map were the lowest daily minimum temperatures recorded at thousands of temperature data stations during each of the years sampled.
  • divides the U.S. into multiple hardiness zones with 10o F differences in average annual minimum temperatures. Zone 1 is the coldest zone (-50o F to -60o F).
  • divides each hardiness zone into "a" & "b" with "a" being the colder half of any zone and "b" the warmer half.

There are changes in the new map and the process that was used to develop it:


    Photo 1: 1990 USDA Hardiness Zone Map

  • The 1990 HZM was based on data from a 12-year period (1976-1990) while the new HZM is based on data from a 30-year period (1976-2005).
  • The data used to create the new map was more complete, and a complex algorithm was used to interpolate between recording stations. Temperature data from more than 8000 temperature data stations belonging to the National Weather Service, the USDA Natural Resources Conservation Service, the USDA Forest Service, the Bureau of Reclamation, and the Bureau of Land Management was used. Average minimum temperatures were then calculated for ½ mile square computer grids for the entire country to create the new hardiness zone map. This was followed by a review process that included climatologists, agricultural meteorologists, and horticultural experts who checked for errors, looked for the source of errors, and corrected errors.


    Photo 2: 2012 USDA Hardiness Zone Map

  • The new map is Geographic Information System-based. This means that the map is more accurate, is interactive (by zip code) to improve user experiences, and has higher resolution that can show smaller areas of zone delineations than before. While the 1990 map was a static image and was not designed for web use, the new map allows users to zoom in to a local area to see the higher temperatures of cities that are heat sinks, the lower temperatures on mountain tops, and the buffering effects of large bodies of water on temperature.

What does the new hardiness zone map show?
In general, the new map shows what we have all been experiencing in recent history: warmer low temperatures during winter. A shift of ½ of a zone was common for much of the country. Closer to home, here is what happened to Minnesota's hardiness zone map:


    Photo 3: 1990 USDA MN Hardiness Zone Map


    Photo 4: 2012 MN Hardiness Zone Map

  • There was a ½ zone shift for much of the state because Minnesota, like the rest of the U.S., has been experiencing warmer annual minimum temperatures during the time period used to create the new HZM.
  • Zone 5a (with average minimum temperatures of -15o to -20o) crept up into the south central portion and the far southeastern corner of Minnesota.
  • Much of the southern ½ of Minnesota that was formerly divided into zones 4a & 4b is now zone 4b (with average minimum temperatures of -20o to -25o).
  • The four pockets of Zone 2b (with average minimum temperatures of -40oto -45o) disappeared from northern Minnesota.
  • The amount of Minnesota that is zone 3a (with average minimum temperatures of -35o to -40o) shrank significantly due to an increasing area of zone 3b (with average minimum temperatures of -30o to -35o).
  • Parts of the far northern shore of Lake Superior that were formerly zones 4b and 4a are now designated as 4a and 3b, meaning they are colder.

What kind of impact should the new hardiness map have on Minnesota gardeners?

  • We can all rest easy knowing that the warmer minimum annual temperatures we have been enjoying over the past years really did happen!
  • Remember that a HZM is created based on average annual minimum temperatures and should only be used as a general guide. By the very definition of average, we know that temperatures lower than the average minimum temperature of the zone you live in will occur. Pick your plants accordingly. Maybe we can broaden the palette of plants we choose to grow in Minnesota a bit, but be cautious and wise in your weighing of risk vs. gain as you trial new plants. Losing an herbaceous perennial or quickly-maturing shrub to winter injury may be of little concern in terms of the time it takes to establish a replacement plant. Losing a slow-growing shrub or a tree that takes decades to grow to mature size creates more pain.
  • Hardiness zone maps are of no help in predicting plant damage or mortality during acclimation and deacclimation. Remember that hardiness is not just about the lowest temperature a plant must survive during a winter. Every year, starting in late summer, perennial plants goes through a multi-month process called acclimation that prepares them for winter survival. In spring dormant plants go through a reverse process called deacclimation that restores their ability to actively grow during the growing season. Plants can be winter-injured or killed by abnormally low temperatures during the months of acclimation and deacclimation too. This is especially true of marginally hardy plants from warmer parts of the country or world that we may try to grow in Minnesota.
  • Hardiness zone maps provide gardeners with one category of plant performance information: winter survival. Good plant performance is not just about winter survival. If the new HZM persuades you to plant cultivars and species new to you, remember that there are other selection categories to consider as you match a plant to your planting site: soil texture, soil moisture, soil pH, light exposure, precipitation, etc.

What's New or What's Good

Kathy Zuzek, UMN Extension Educator, Horticulture

An enormous interest for most gardeners during our long winter is the search for new cultivars that can be added to next year's garden. But is new always good? The answer to that question depends on whether new cultivars have been shown to perform well in Minnesota gardens before their introduction into garden centers. Horticultural professionals should provide customers with the best performing plant selections for Minnesota's difficult climate. But the current trend in horticulture is to move new plants onto the market in the shortest possible time frame, creating a rapid process of both cultivar introduction and elimination in the market.

This creates several problems for gardeners interested in sustainable gardening and in planting cultivars known to have long-term landscape value. New cultivars are now introduced to Minnesota gardeners from breeding and evaluation programs around the world. When new cultivars are rushed to the market, there is often no time for the evaluation of the plant's performance in Upper Midwest gardens prior to introduction. Purchasing and planting new un-trialed cultivars among annuals or herbaceous perennials may be an acceptable risk for gardeners to take. These plants are relatively inexpensive and establish and grow to maturity quickly. It is much riskier in terms of money, labor, and time invested if gardeners purchase and grow un-trialed shrubs and especially trees that take decades to reach maturity.

If newly introduced cultivars are displaced quickly by even newer cultivars, there is also little time to evaluate their long-term potential in the landscape between their introduction and their elimination from nursery catalogs. This sets up a situation where newer cultivars prove to be a good performer in our Minnesota gardens but by the time this fact is recognized, the plant has already been removed from nursery catalogs.

The emphasis on new cultivars may also result in the elimination from the nursery trade of much older cultivars as they are removed to make room for new cultivars in a nursery's production schedule. The introduction of new cultivars that have been shown to be improvements over older cultivars is an exciting event for gardeners, especially for northern gardeners who have a smaller pool of plants to choose from than southern gardeners. But what if older cultivars that have proven their long-term landscape value over decades of time are replaced with un-trialed cultivars that fall short of the mark?

As wise gardeners, we can help solve these problems by asking "What's good?" rather than "What's new?" Finding information on plant performance in Minnesota or the Upper Midwest can be a tough go though. Here are some suggestions:

Take advantage of the information available from plant evaluation programs. Plant evaluation programs for the Upper Midwest are few and far between but here are a few examples:

  • The Chicago Botanic Garden has been home to the Plant Evaluation Program for 28 years.

    Kathy Zuzek

    Photo 1: Plant Evaluation Notes

    The goal of this program is to determine, through scientific evaluation, which annuals, perennials, vines, shrubs, and trees are superior for gardens in the Upper Midwest. Information on the program and the 35 Plant Evaluation Notes published to date can be found here.

  • The All-America Selections program was founded in 1932 and is a national program that annually evaluates and identifies new garden seed varieties with superior garden performance based on impartial trialing at 47 sites throughout North America. The horticultural garden at the West Central Research and Outreach Center in Morris, Minnesota is home to one of these test sites. More information on this evaluation program can be found here.

  • Look for information on cultivar introductions and evaluations from universities and their affiliated Extension services in the Upper Midwest.
  • The University of Minnesota's Department of Horticulture is home to research programs that develop cultivars of turf grasses, herbaceous perennials, ornamental shrubs and trees, and fruit crops. Cultivars developed through the efforts of these research programs are highlighted here in a publication titled Minnesota Hardy. Information on garden plant selection can also be found on the University of Minnesota Extension Garden web page.

  • North Dakota State University's Department of Plant Sciences has selected 42 ornamental shrub and tree cultivars that perform well in North Dakota's Zone 3, low moisture climate. Many of these cultivars perform well in Minnesota too. Information on these cultivars can be found here.
  • Ask for information from your knowledgeable gardening friends, garden center staff, and any landscape design and maintenance professionals whose objective knowledge you value. Cultivar information provided by knowledgeable friends and objective horticultural professionals may be anecdotal, but this is often the best information we have given the dwindling support for formal plant evaluation programs. These are the people who will know plants that have stood the test of time in Minnesota landscapes.

    Visit the Minnesota Landscape Arboretum grounds and website regularly to view plants that are hardy enough to grow in Zone 4 and sometimes Zone 3. The arboretum is home to thousands of ornamental cultivars of annuals, herbaceous perennials, ornamental shrubs and trees, and vegetable and fruit cultivars.

  • Information on the locations of cultivars of particular interest to you is readily available from arboretum staff.

  • Use the arboretum as an outdoor classroom. A few visits during the year can provide you with practical information on cultivars of interest to you. Observing plants during their seasons of interest whether it is during bloom display, fruit display, fall color, or in winter, can be most helpful. Visits in late summer and early fall to view overall plant appearance give good visual information on how well a plant has tolerated disease and insect pests throughout the growing season.

  • Check out the plant labels as you observe perennial herbaceous or woody cultivars you are interested in. Labels of plants in permanent plantings will have an 8-digit number on them. The first four numbers will give you a close approximation of the year the cultivar was planted, plant age, and how long the plant has been growing at the arboretum. For example a label reading "19880247" indicates a plant that was planted in 1988 or shortly afterwards.

  • Kathy Zuzek

    Photo 2: Plant Info link on the arboretum website

  • Check out the Plant Info tab on the arboretum website.

    A visit to this webpage can provide information on wholesale and retail nurseries that provide mail order service and carry your plant of interest. The webpage also has links to and lists of other websites, books, and magazines carrying information about and photos of your plant of interest.

  • Espalier - An Art Based on Science

    Karl Foord, UMN Extension Educator



    Espalier is a plant shaping/pruning method where plants are grown in a single plane limiting their height and width to a defined area. The area is usually defined by a permanent framework which stabilizes the plant. The espalier is developed and maintained by pruning techniques of which timing is a critical part, for a pruning cut made in early spring will likely have different results than one made in midsummer.


    Role in the Landscape

    Espalier takes on a number of high profile roles in the landscape. It can be the focal point of the landscape design or take on lesser roles as privacy screens or backdrops. It can function as a key plant softening the appearance of walls or act as an accent or specimen plant. An accent plant has year around interest like most evergreens. A specimen plant has seasons of interest such as flowering, fruiting or attractive bark. Because the espalier technique reduces the number of leaves on a plant, the stems, bark texture, leaf shapes, flower and fruit are more exposed and emphasized. Due to its spatially defined nature, espalier makes efficient use of space and permits a greater variety of plants than if full sized plants were used.

    Espalier is a gardening technique of long standing. It has been practiced in gardens of Egyptian Pharaohs, middle age monks, and French kings. One of the more famous locations where espalier is on display is at Claude Monet's garden in Giverny, France (Exhibit 1 & 2).

    Espalier techniques

    Mastering espalier technique involves understanding how the plant responds to pruning cuts and shape manipulation. It involves choosing the buds one wants to form the branches that will create the desired shape. At least four techniques are essential to success.

    The first involves cutting and bud orientation. When a terminal bud is cut, its hormonal inhibition of buds down the stem is released and the cut stem establishes many branch point s (Exhibit 3). The idea is to make the cut above the bud facing in the direction you want the stem to grow.


    The second involves knowing how to bend a branch. Branches should be bent when they are young and most supple. The best way to proceed is to attach the branch to a splint prior to the bend (Exhibit 4) and bend the branch over a few weeks time, adjusting the angle of the branch 5-10° at a time (Exhibit 5). Care should be taken to not girdle any stem with plant ties and to move them annually if necessary.



    The third involves maintaining the plant within the proscribed limits by precise pruning of the branch laterals and sub-laterals (Exhibits 6 & 7). This serves to limit the length of stem growth, and encourages the development of fruiting spurs.



    Fourth involves eliminating unwanted buds through the technique of rubbing. Should a bud exist in a place where a stem is not desired, the bud is removing by rubbing it off the stem (Exhibit 8).


    An example of an espaliered apple (Exhibit 9) as well as many other plants can be observed at the Landscape Arboretum.


    Want to know more?

    This article is by necessity a very basic introduction. A very helpful book on the technique is, Espalier: Essentials of the Candelabra Pattern by Katherine Aby. Espalier can be appreciated and understood from books but, espalier techniques are truly learned and developed by practice. There will be an opportunity to observe and practice next month. Katherine will be teaching a one day class on the basics of espalier on Wednesday, June 15 to interested parties. Location will be based on # of registrants being either in South Minneapolis or closer to the Arboretum. If you are interested please contact Katherine at:

    Special thanks to Katherine Aby for the use of her illustrations. More illustrations and a more detailed discussion of techniques can be found in her book, which can be obtained on her website .

    You buy a plant at a garden center. Where did it come from?

    Karl Foord, UMN Extension Educator


    Vanilla Strawberry™, Hydrangea paniculata 'Renhy'PP20,670

    To answer this question I traveled to Newport, Minnesota to visit with Debbie Lonnee who is a Planning and Administration Manager at Bailey Nurseries. Don't be fooled by the title, Debbie knows hers plants intimately. Listening to her describe plant cultivars is like watching Monet paint.

    Bailey Nurseries

    Bailey Nurseries celebrated its 100 year anniversary in 2005 and is still managed by fourth generation members of the Bailey family. Bailey has production locations in Minnesota, Illinois, Iowa, Oregon, and Washington where it produces and distributes fruit and shade trees, ornamental shrubs and vines, roses, evergreens, fruits, perennials, and annuals. As a wholesale operation they sell to over 4500 retail garden establishments, landscapers, and growers located in 47 U.S. states as well as Canada, Europe, South Africa, Australia, and Japan. Try to imagine the effort involved in getting this wide variety of plants delivered bellaanna.jpg

    Bella Anna™ Hydrangea arborescens 'PIIHA-1' PPAF

    at the right time of year for each of these locations. It boggles the mind.


    Endless Summer® Blushing Bride™ Hydrangea, Hydrangea macrophylla 'Blushing Bride' (PP17,169).

    Breeding efforts and partnerships

    The breeding efforts focus on improved habit and ornamental qualities, and disease resistance to name a few among a host of characteristics. The disease resistance objective is particularly noteworthy as its goal is to eliminate chemical treatments and to replace plants which have been shown to be particularly susceptible to diseases. Bailey has a breeding program but they do not restrict their efforts to their own program, as they solicit breeding partners from around the world. This greatly increases their reach and at the same time increases our exposure to newly produced plants. To get a sense of how this brings plant opportunities to you and me, I asked Debbie to trace the development of three new cultivars.

    New Cultivars

    One of the new cultivars is 'Vanilla Strawberry™' which is a Hydrangea paniculata with conical shaped flower. The interesting thing about this cultivar is that the flower starts out stark white and gradually changes from white to pink from the bottom up. This cultivar came from a partnership with SAPHO, an organization formed between French breeders and the Angers branch of the French Research Institute (INRA). Presently there are 20 breeder/stockholders including M. Renault, the breeder of 'VANILLE FRAISE ® 'Renhy'.


    Twist-n-Shout® Big Leaf Hydrangea, Hydrangea macrophylla 'PIIHM-I' PP20,176

    Another new cultivar is 'Bella Anna' which is a Hydrangea arborescens from the Endless Summer® series of reblooming Hydrangeas developed by Dr. Michael Dirr who spent most of his career at the University of Georgia. 'Bella Anna™' produces giant pink flowers that can measure up to 10 inches across. It is in essence a pink 'Annabelle' hydrangea.

    It should be noted that H. arborescens does not change flower color in response to soil pH. The three other cultivars in the Endless Summer ® collection (Endless Summer™, Blushing Bride™, and Twist-n-Shout™) are all H. macrophylla species which does respond to soil pH. There are products called Color Me Pink™ and Color Me Blue™ which will change the color of your hydrangea flowers. The flowers become Pink in alkaline soil (pH greater than 7), and blue in acidic soil (pH less than 7).

    A third cultivar is 'Little Devil™' Ninebark which is a Physocarpus opulifolius. This cultivar was bred by Dr. David Zlesak who was the previous editor of the Yard & Garden News and now a professor at the University of Wisconsin-River Falls (UWRF).
    One of the advantages of this cultivar is its size. David was able to introduce a dwarfing gene creating a 4 foot tall dark leaved ninebark vs. a 10 foot tall 'Diablo' dark leaved littledevil.jpg

    First Editions® Little Devil™ Ninebark Physocarpus opulifolius 'Donna May' PPAF

    shrub. Much of today's breeding work focuses on creating small stature or dwarf varieties. This permits traditionally larger plants to fit into today's smaller landscapes as well as permitting a greater variety of textures, forms and colors for the landscape palette.

    Last spring Twin Cities Live did a short segment on Bailey Nurseries, in which they showed a number of the production systems and facilities. This video is no longer available.

    All photos courtesy of Bailey Nurseries.

    What are your woody plants doing right now?

    Karl Foord, UMN Extension Educator

    Well, here we are in Minnesota where most parts of the state are sitting under several feet of snow. This led me to think about what was the state of my apple and maple trees.
    The plants in our state are adapted to northern climates with harsh winters that are unfavorable to plant growth. One mechanism that these plants have adopted to survive involves a suspension of growth termed dormancy.

    The bud that overwinters in an apple tree is a miniature shoot with apical meristem, leaf and perhaps flower primordial, and axillary buds enclosed by modified leaves termed bud scales. Bud scales protect the bud from mechanical injury, restrict gas exchange and prevent desiccation.

    Preparation for winter and true dormancy
    KFTbl.jpgThe buds are the photoperiod receptors and in preparation for winter undergo a series of physical and physiological changes triggered primarily by the shorter days of late summer. These short days (actually long nights) trigger the production of abscisic acid (ABA) which acts as a growth inhibitor. ABA has been found to build up to high levels in the fall. Although cool temperatures are not the primary trigger they facilitate dormancy of the buds. There is a point at which the bud cannot be induced to grow even given under optimum environmental conditions. At this point the bud is said to be in true dormancy. The only way the bud can be induced to grow is by experiencing a chilling period. Temperatures need to be below 45° F (7.2° C) and last for between 800 and 1,000 hours for northern adapted apples (Table 1). It may be the presence of ABA that inhibits growth and only after this inhibitor decays over time that the plant has the ability to respond to favorable environmental conditions. This removes the internal block to growth, but external factors such as low temperature can also inhibit growth in the early spring.

    Dormancy can be distinguished from quiescence where the bud is in a resting state in response to adverse environmental conditions, but will resume when the environmental conditions become favorable again. Fascinatingly enough, roots overwinter in a in a quiescent state.

    When the soil begins to warm, promoters of growth such as gibberellin and cytokinins build up, signaling the bud to resume growth.

    Intracellular water management for plants in cold climates

    Another aspect to surviving harsh winters other than the dormancy state is the management of cellular water either through deep supercooling or intracellular dehydration. Temperate woody plants utilize one of these two mechanisms.

    Supercooled water is water below 32° F (0° C) that remains in a liquid state. Supercooled water can remain in the liquid state down to -36.6° F (- 38.1° C) and in the presence of dissolved solutes to -43.6° F (-42° C). This temperature is called the Homogeneous Nucleation Point. Without nucleating points no ice crystals will form above this temperature, and plants avoid cold damage by not allowing nucleating points. At temperatures below -43.6° F (-42° C) ice will form and the plant cells will be damaged or killed. Most temperate plants in North America utilize this mechanism.

    Plants growing in parts of the world where temperatures fall below -43.6° F (-42° C) utilize a different mechanism. These plants avoid injury by preventing intracellular (within the cell) ice formation. Water freezes in the extracellular spaces which pulls liquid water out of the living cells leaving them dehydrated. These plants avoid damage by freezing but can be injured by dehydration. This mechanism permits plants to survive in areas where the temperatures drop below -43.6° F (-42° C).

    What's Happening at the Plant Disease Clinic

    Karl Foord, UMN Extension Educator
    Dimitre Mollov - Director of Diagnostic Services, UMN Plant Disease Clinic

    Dimitre Mollov Plant Disease Clinic_pptx [Read-Only]_2.jpg

    Dimitre Mollov at his dissecting scope. Karl Foord.

    Every year brings its unique weather but 2010, with its unseasonably warm April and our cool and wet late May and June, presented some ideal conditions for disease. To explore this further I visited with Dimitre Mollov, the Director of Diagnostic Services of the Plant Disease Clinic of the University of Minnesota. Dimitre took over leadership of the lab some three years ago and to date has analyzed some 6,500 samples from 22 states. These samples have included some 1000 pathogens on some 300 hosts. Eighty plus percent of the samples come from commercial entities where control decisions have greater financial impact, but there may be times when it might be worth it for a homeowner to send a sample to the clinic. How are samples processed and how are the results analyzed at the clinic?

    The challenge in diagnosis

    You can see the challenge in diagnosis when someone hands you three leaves and asks what is wrong. Sometimes this can be easy with clearly diagnostic insect chewing or piercing damage or pathogens with characteristic necrotic lesions. However there are times when the evidence is asymptomatic, or confounded by more than one organism, or saprophytes who have followed wounds created by other means or organisms. This is why the information sheets submitted with the sample are so important; the more that is known about the specific situation the more information there is to work with in complicated situations.

    The importance of information beyond the sample

    A well supported sample has information about the plant's symptoms and what parts of the plant were affected. Is there a pattern observed such as the problems began at the top of the plant and worked their way down or started at the bottom and worked their way up. Were other plants in the area affected? When were the symptoms first observed? Other information about the site such as slope, or predominant compass direction of exposure is helpful. The soil type and drainage of the site as well as other chemical inputs to the situation are useful to the diagnostician.

    Dimitre Mollov Plant Disease Clinic_pptx [Read-Only]_3.jpg

    Karl Foord.

    The importance of soil analysis

    As an example, a sample that had just been received was a three year old Fir tree sent in by a Christmas tree grower. The small tree was about two feet tall and the length of annual growth nodes had been decreasing for the last two years (Exhibit 1). In this case there was no evidence of the presence of an insect or disease pathogen. Given this one would have to expect abiotic factors. Also this stunted growth was not uniformly distributed throughout the field. It is possible that the tree is experiencing problems associated with a high pH soil. See the Climate and Site Requirements section of the publication entitled Choosing Landscape Evergreens. However, in this case a soil analysis had not been performed and the diagnosis could not be definitive. Dimitre recommends having a soil test done before sending in samples for pathological analysis. Having such basic information is a good base from which to continue diagnosis. But what if the sample does show other symptoms?

    A systematic approach to diagnosis

    The approach I learned from Jeff Hahn and Michelle Grabowski is to first look for insect damage which is typically at a macro level and can be viewed with the naked eye. The next step is to look for signs of fungal or bacterial pathogens. Dimitre begins this at a macro level with a dissecting scope (picture) and confirms identification with a microscope (picture). He will look for characteristic fungal structures such as spores or mycelia or evidence of the presence of bacteria from cell breakdown or lysis. Should these forms of identification not be present Dimitre has the ability to perform laboratory tests for viruses. Correct diagnosis of viral diseases normally requires laboratory tests because symptoms induced by viruses can also occur due to adverse environmental conditions. Common laboratory tests include identification of specific proteins of the virus by ELISA (enzyme-linked immunoasorbent assay) or DNA of the virus by PCR (polymerase chain reaction).

    Some of these tests for viruses are now available to the commercial grower or passionate homeowner. One supplier is Biobest who make Flashkits for viral detection.

    The lesson I took from my visit to Dimitre is as follows: Understand your limitations as a diagnostician and the environmental impacts of your decision. If you cannot identify the pathogen with certainty, avoid application of environmentally potentially harmful chemicals that may have little impact on the problem. To help in diagnosis you can use the diagnostics section of the extension website.

    If you want more information about the clinic or to obtain sample submission instructions and forms, please go to the UMN Plant Disease Clinic website.

    The following case was brought forth by Detective Marian Kleinwort PSI ISU. The facts of the case were:

    Paulownia.jpg1. Original purchase 6 years ago as seed from catalog - unknown; plant name - unknown

    2. Leaves appear on new stems at the end of May into June

    3. Stems grow very fast in summer sometimes reaching 15 ft.; one witness reported that some of the stems grew 12 - 15 inches in one day this summer

    4. Witnesses reported that all growth in the picture was from this year's growth

    5. No flowers are produced

    6. Leaves do not change color in fall

    7. Stems are solid early but become hollow later in the year

    6. Each year the shoots die back to the ground and new shoots appear

    9. Clumps of the plant have been given to neighbors who report that they have had the plant for 3 years

    10. A similar plant is believed to have been observed in a neighboring town

    Special Investigator Dr. Mary Meyer was called in as a special consultant on the case. Her findings were as follows:

    Genus and species Paulownia tomentosa; Family: Bignoniaceae

    Common name: princess-tree; Synonym(s): empress-tree

    Consulting Plant Psychologist Dr. Karl Foord was asked to explain the bizarre behavior of this plant.

    His findings are as follows:

    Plant is reportedly hardy to zone 5b. When growing in its adapted environment its leaves will turn yellow in the fall. Apparently the early frosts kill the leaves before they develop color. It appears that the underground trunk tissue is not killed in this climate and new sprouts appear each year. The great vigor of the young shoots is characteristic of this plant. Because the stems never survive more than one year, any flower buds produced in the first year of growth are killed. This is exactly the way my non-northern strain of Redbud (Cercis canadensis) plants behaves. No trunk is ever established and the plant produces several trunk sprouts which die back to the ground each year.

    Editor's note: Thanks to Marian Kleinwort, UMN Extension Master Gardener - Dodge County, for submitting pictures of the sample and the facts about the case. Thanks to Dr. Mary Meyer, UMN Horticulture Science Professor, for identifying the plant.

    Plant Hardiness Zones Revisited

    Karl Foord, UMN Extension Educator

    If a particular temperature recording station has an average minimum low temperature of between - 30F to - 25F then the station would be in 4a. If the range was - 25 F to - 20 F then this station would be part of the 4b hardiness zone. The same logic determining the temperature ranges for Zone 2b [-45 to -40 F], Zone 3a [-40 to -35 F], and Zone 3b [-35 to - 30 F].


    The average part of this calculation gave me concern because if it is an average then there must be numbers less than and greater than the average. The question then becomes how wide is the distribution around the average?

    Minneapolis is in the 4a plant hardiness zone with a low minimum temperature range of -30 F to - 25 F. Over the last one hundred and eleven years low minimum temperatures have exceeded this range 10% of the time, but only by four degrees at the most1. Temperature data for the last 10 years (2000-2009) places Minneapolis in hardiness zone 4b. If we are willing to accept a 10% chance of a low minimum beyond the -20 F to -15 F range, then Minneapolis would be placed in zone 5a. The question is how many of your 5a plants would have died given the low temperature of -24 on January 30, 2004. The relatively milder recent winters gave rise to a revised plant hardiness map that can be viewed here. This map was subsequently rejected by the USDA.

    I think it is critical to point out that the low minimum temperature is only one of a number of factors that come to play on a plant's winter hardiness.

    Other factors include snow cover, temperature patterns favoring the development of dormancy, moisture conditions, and microclimate effects to name just a few.

    Snow cover
    Snow functions as an insulator protecting the root system of overwintering plants. Nine inches of snow can lead to a 42 F differential between a - 14 F air temperature and a 28 F soil surface temperature.


    Reliable snow cover increases the temperature that the plant experiences and puts the region in a higher plant hardiness zone. This is why locations like the Upper Peninsula of Michigan are functionally zone 5 due to consistent deep snow falls, whereas without this snow the UP would likely be zone 3a.

    Temperature Patterns Favoring the Development of Dormancy

    The plant's ability to withstand cold temperatures is a function of the metabolic status of the plant. If the plant experiences gradually decreasing temperatures and is allowed to achieve full dormancy then it has achieved its optimum genetically programmed degree of winter hardiness. However in winters that are warm in the beginning of December followed by a significant temperature drop to average temperatures at that time of year, the plants are not metabolically prepared and will be damaged.

    Moisture Conditions

    Cold dry winds tend to desiccate plants especially evergreen plants with exposed leaves. Plants entering winter under draughty conditions are further stressed leading to weak plants and mortality.


    Local conditions can modify the climate experienced by the plant. Protected locations reduce the stress caused by cold dry desiccating winds. Highly exposed locations can increase plant stress. Slope affects airflow as cold air sinks into lowland areas called frost pockets. South facing hillsides capture more heat which can be advantageous for plants like grapes, but disadvantageous if the heat stimulates early flowering subjecting the plant to the risk of late spring frosts. There is an art to finding the right plant for the right location. I am a big fan of Japanese maples. Their microclimate over the winter is my garage. I for one am not willing to accept the risks of the one in ten chance of a true 4a or even 3b winter that we might experience in the Minneapolis area zone 4a. Especially consider microclimates if you live in 4a or 4b and have a lake home or cabin in 3b or 3a.


    Data from the Minnesota Climatology Working Group for Minneapolis

    February 2010 Garden Calendar

    Contributors: Karen Jeannette, Research Fellow and Yard and Garden News Editor;  Michelle Grabowski, Extension Educator;  excerpts from the 2010 Minnesota Gardening Calendar, and Arboretum News Feb/Mar issue.

    Plant tips

    Seed & Plant Selection


    Photo:Seed catalog cover from 1913. A mini-exhibit of seed catalog covers can be seen in walkway from the restaurant to the Snyder building at the Minnesota Landscape Arboretum. Anderson Horticultural Library. Pre-copyright.

    • Read seed catalogs and favorite gardening magazines for new ideas.  Good planning now allows you to avoid some impulse purchases later.  Look for flower and vegetable cultivars with superior disease-resistance, but check that they'll mature in our relatively short growing season.  Seek out perennials rated hardy enough for Minnesota: USDA 3 in the north, zone 4 in the southern two-thirds of the state, and possibly zone 5 for well-sheltered parts of the Twin Cities. (Zone 5 plants are always more risky). -- This is a 2010 Minnesota Gardening Calendar Tip.

    • Visit the The Anderson Library, located at the Minnesota Landscape Arboretum, to view the new 2010 seed catalogs arriving daily.   The catalogs now number more than 1, 000!  For those that can't make it to the library in person, the Anderson Library also hosts seed catalog information available at Plant Information Online (  Want to learn more? There are several ways you can learn more about using Plant Information Online? See the video @ ttp:// or attend a class. Plant Information Online Classes will be held: Feb. 9 & 23, Mar 9 & 23; 10:30 - 11 a.m. or arrange a time to stop in.  Call the Library for help at 952-443-1405.

    Pruning Advice

    • Have shade trees and fruit trees professionally pruned this month or next.  It's easier to see a tree's structure when no leaves are present, and the fresh cuts won't pose a disease or insect problem to oaks, elms, apples, or other trees when pruned in winter.  Some trees, such as maples, birch, honeylocust are likely to drip lots of sap from wound sites in spring, but they should be fine as long as no more than 25% of their canopy was pruned out.  This is definitely not a do-it-yourself project, though.   For more information on hiring professionals to prune shade trees, see: Knowing When to Hire an Arborist -- This is a 2010 Minnesota Gardening Calendar Tip.

    Valentines Flowers

      • Keep Valentines Days flowers attractive as long as possible by setting them in a cool location when you're not around to enjoy them.  Put them in a spotlessly clean vase filled with barely warm water and floral preservative.  Add more water and preservative solution as the level drops, replacing it as soon as it appears cloudy.  Trim off any foliage that would sit below water, as it rots easily, and make a fresh cut at the base of each stem whenever you change the water. -- This is a 2010 Minnesota Gardening Calendar Tip.


    • The Minnesota Landscape Arboretum will present "The Great Hall of Orchids--Passport to Paradise," Feb. 12 through March 14. A preview event is scheduled for Feb. 11. The exhibit will feature a variety of orchids--including many unique species and hybrids--all grown by renowned orchid expert Jerry Fischer and his Orchids Limited greenhouse of Plymouth. The orchids will be displayed in the Great Hall of the Oswald Visitor Center. Free with arboretum gate admission.

    Planning the 2010 Garden with Minnesota Gardening Information

    Karen Jeannette, Horticulture Research Fellow & Yard and Garden Editor

    2009-2010 gardenplanning.jpg

    Photo 1: What are your gardening plans for 2010? Karen Jeannette.

    For many gardeners, the gardening season starts as soon as garden catalogs arrive and seed packets are back on the shelves of garden centers and nurseries. At this time of year, it's tempting to choose the flower varieties that most quickly jump off the page of gardening catalogs with the newest improved colors, or to select vegetables packets with photographs of the most succulent varieties you've ever seen. While sometimes those varieties are in fact winners, Minnesota growing conditions can challenge the best of the best nationally rated varieties, not to mention those that are just the best photographed.

    Finding a stunning specimen or exceptional deal on a plant is always a thrill.  However, when trying to get the best value from your plants in 2010, don't forget that finding the right plant for its growing conditions can create much value through benefits such as improved growth, insect and disease resistance, and fewer maintenance needs.

    Choosing varieties to grow for the coming gardening season is a common garden task for many in January. Yet for some, formulating overall landscape plans to meet site conditions and functional goals must come first.  Among hundreds of resources at the University of Minnesota Gardening Information website ( ), here are a few highlighted resources to start gardening with for 2010.

    •  U of MN Annual Flower Trial 2009 - Find the 2009 Annual Flower Trial's top performing annual flower cultivars that are likely to be seen on the market in 2010 or shortly after.

    • Starting Seeds Indoors - A guide to growing plants from seeds, including tips for buying seed and supplies, planting, and how to successfully grow seedlings for transplanting into the garden at the right time.

    • The Best Plants For 30 Tough Sites - Trying to find out which plants are deer resistant, what grows in dry shade, or which annuals are more cold tolerant than others? University of Minnesota Extension Service Master Gardeners draw on their 30 + years of teaching and experience to provide this list of plant selections for 30 tough sites.
    • Thumbnail image for Thumbnail image for AppleTreewithladder_medium.jpg

      Photo 2: Enjoy the bounty by choosing Minnesota hardy fruit varieties. Karen Jeannette.

    • Landscaping - January is a great time to formulate landscape plans. The landscaping section of garden information provides many resources to help you get started.

    • Use Diagnostics and Wildlife for troubleshooting last year's plant problems so you can formulate appropriate plans and prevention strategies for 2010.

      Find More Minnesota General Gardening Information by Topic

      Go to:
      • University of Minnesota Gardening Information website @
      • Find the plant topic your interested in the left-hand column under the "Find information on" heading
      • Seek out the general information sections about the topic to learn more

      Screenshot (below): Finding general plant information by plant topic @

      U of M_ Gardening Information_ Information - Vegetables-2-2-1_Medium.jpg

      Quick Update on Colorado Potato Beetles

      Jeffrey Hahn, Asst. Extension Entomologist

      Do you have a problem with Colorado potato beetles in your garden? If you grow potatoes, there is a good chance you see them at one time or another on your plants. Don’t forget that in addition to potatoes, they can also attack eggplants, tomatoes and peppers. This insect can be challenging to manage but here are a few tactics you can use to deal with this pest.

      Monitor susceptible plants regularly so you know if Colorado potato beetles are present in your garden. If you have a history of these insects in your garden, the odds are good you will see them again. Because you can have overlapping generations, you can find all life stages in your garden at any given time. Once they are active in spring, you will generally have Colorado potato beetles in your garden all summer.

      If you have a smaller garden, and the time, handpicking is a great nonchemical control method. To be sure they are killed, just toss adults and larvae into a bucket of soapy water. For the really small, young larvae, just put on your gloves and squish them. And don’t forget the eggs. Look for them on the underside of the leaves. They are easy to recognize as they are orange and in clusters.

      If physical removal is not practical, you may wish to use an insecticide. There are two low impact products available. Spinosad is produced by the fermentation of a soil-dwelling bacterium, Saccharopolysora spinosa. It is quick acting, attacking the nervous system of insects. It is most effective against caterpillars, flies (mostly leafminers), and thrips, as well as leaf beetles, grasshoppers and other insects that consume a lot of foliage.

      art5-2_600.jpgNeem is derived from the neem tree, a plant found in arid tropical and subtropical areas. Neem can deter insect pests in one of several ways. They can inhibit their feeding, repel them, or disrupt their life cycle preventing them from successfully molting. Neem is generally effective against a wide array of insects, including beetles.

      You might be wondering about Bacillus thuringiensis var. tenebrionis, a commonly used home garden product for leaf beetles, like Colorado potato beetles. This bacterial insecticide, which acts as a stomach poison, is quite effective against young larvae. However, this product is no longer registered in Minnesota. It was previously available from Bonide in a product called Colorado Potato Beetle Beater. If you look at Bonide’s products, you will still find a product with that name, but it now contains spinosad.

      There are a wide variety of residual insecticides, such as permethrin and carbaryl that are labeled to treat Colorado potato beetles. However, there is a good chance that the Colorado potato beetles in your garden are resistant to these insecticides already. This will be particularly true if you are any where near a commercial potato field. Instead try a newer insecticide, like esfenvalerate. The beetles in your garden are more likely to be susceptible to it.

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