University of Minnesota
University of Minnesota Extension
myU OneStop

Yard and Garden News

Extension > Gardening Information > Yard and Garden News > Trees & Shrubs Archives


October 1, 2009

What's Up With That?!

Birch Abnormal Growth Syndrome (BAGS) aka. Mouse Ear Disorder

Carl Rosen, Extension Soil Scientist and Karl Foord, Extension Educator

10-1-09_Med-Summer Cascade Birch 8 6 2009 cropped_KarlFord.jpg
The strange leaf symptoms on this river birch tree, taken on August 7 (Photo 1, left) were diagnosed as birch abnormal growth syndrome or BAGS. New leaves are severely stunted and take on a mouse ear appearance. For many years the cause of this disorder was a mystery, but it is now known to be due to a deficiency of nickel.

Photo 1 (left): River Birch 'Summer Cascade' at planting time showing symptoms of nickel deficiency (BAGS). Photo taken August 7, Karl Foord.

Nickel is an element only recently shown to be essential for plant growth and is required in very small amounts. Almost all soils have enough nickel to support plant growth, but under some conditions, nickel deficiency can still occur. The mouse ear symptoms on this river birch were first seen when growing in a peat-based container mix, and were initially misdiagnosed as bud damage from a late frost. However, after the tree was transplanted into the soil in mid-May, the symptoms, after continuing for the next few months, have now begun to appear normal.10-1-09_Med-Summer Cascade Birch mouse ear.j_CarlRosenpg.jpg

Based on research conducted at the University of Minnesota and in other areas of the country, BAGS almost exclusively occurs on river birch when grown in peat-based media and can be corrected by soil or foliar applications of nickel.

Photo 2 (right): Close up of 'Summer Cascade' river birch leaves with BAGS. Photo taken August 7, Karl Foord

Research has also shown that when soil is added to the peat media (20-30% by volume), the nickel deficiency symptoms will not occur, suggesting that there is enough nickel in the added soil to meet the nickel requirements of the plant.

10-10-09_Med_nickeldefonriver birch_carlrosen.jpgIn cases where the symptoms are most severe, an analysis of the peat has shown excessively high levels of zinc. These high levels of zinc in the peat likely accentuate the nickel deficiency. Therefore, adding soil to the peat mix may help by 1)alleviating BAGS symptoms by adding the needed nickel,  and 2) by tying up or diluting some of the excessive zinc in the peat.

Photo 3 (left): Up close. Mouse ear symptoms of nickel deficiency on peat-based media. Carl Rosen.

As shown by the picture taken on September 14 (Photo 4, below), the tree has nearly recovered from its mouse ear symptoms and is expected to make a complete recovery once the roots have fully established into the native soil. 

10-1-09_Med-Summer Cascade Birch 9 14 2009 recovered_KarlFord.jpgIn general, BAGS has been a problem most apparent to the nursery industry, as trees showing the symptoms are usually not sold. However, if the problem does occur in containers, it can be corrected with nickel applications or by transplanting to a medium containing at least 20% soil. Soils in Minnesota have enough nickel to support plant growth, therefore nickel application to river birch growing in the landscape is not necessary.

Photo 4 (left): Recovery of river birch 'Summer Cascade' from BAGS.  Photo taken September 14, Karl Foord.

Components of and Factors Influencing Fall Color

The tree's response to the decreasing day lengths in the fall is to form an abscission layer at the base of each leaf. As this layer forms, it slowly cuts off water and mineral supplies to the leaf and reduces the manufacture of chlorophyll. As chlorophyll supplies decrease, previously masked carotenoid pigments in the leaf become visible. Carotenoid pigments are split into two classes based on oxygen content: xanthophylls and carotenes.   Xanthophylls, which contain oxygen, are yellow. Carotenes, which do not contain oxygen, are orange. Carotenoid pigments absorb light energy like chlorophyll and serve to protect chlorophyll molecules from photo damage. A carotene you may have heard of is β-carotene which is a precursor to vitamin A. In humans, vitamin A is a pigment essential for good vision.

10-1-09_Med_maplesturningcolor_upclose.JPGAnthocyanin pigments are another important component of fall color, contributing reds and purples to the fall palate. These pigments are not present in the leaf during the active growing season, and form in the leaf in the fall. Anthocyanin pigment formation is a function of sunlight, which is why you may see leaves at the tops and southern facing parts of trees turning colors before the rest of the tree.  When the first leaves of the season fall, the remaining leaves receive more light and develop more color. This phenomenon can also be observed in wooded areas where trees on the edge of woods or those that are taller develop color first.  The smaller trees that have been shaded by taller trees will not develop color until sunlight reaches them.

Photo 1 (left): Maple turning fall colors. Note the outer most leaves exposed to the most sunlight are turning first. Karen Jeannette

Anthocyanin pigments are also present in many fruits. For example, if you see an apple that is highly pigmented on one side and not on the other, it may be because the colored side was exposed to light and the other side was shaded by leaves. Many of our favorite fruit species, such as blueberries, cranberries, raspberries, blackberries, cherries, grapes, and eggplant contain anthocyanin pigments.

Functions of superior fall color

One environmental component that does not add to fall color is frost. A severe frost that is premature will kill the leaf cells and not permit the colors to develop. The leaves will instead turn brown, and drop

Superior fall color displays are a function of weather and the condition of the trees. When healthy, pest free plants with sufficient nutrients and water experience bright, sunny, and cool autumn days, and cool but not freezing autumn nights, we are treated to a magnificent display of fall color. Varying weather conditions can influence the timing of fall color. To get an up-to-date fall color report go to the following website.

The following figure shows the average time "peak" color is obtained in different parts of Minnesota.

Image courtesy Explore Minnesota @


August 14, 2009

Getting Hydrangeas to Turn Blue

David C. Zlesak and Gail Soens, University of Minnesota Extension Educator and Bailey Nurseries New Variety Coordinator / Section Grower Bud and Bloom Hydrangeas & Roses

Blue hydrangea in landscapeWith so few true blue flowering shrubs for our landscape, it is no wonder so many of us are drawn to the beauty of blue hydrangeas! Only one species of hydrangea we commonly see for sale and in our northern landscapes include cultivars that can be coaxed to bloom a true blue or, if desired, a pure pink. It is Hydrangea macroplylla which is also known as the bigleafed hydrangea. Endless Summer® is the most common cultivar of this hydrangea we see for sale in the north as it is able to bloom off of both old and new wood. This is unlike most other H. macrophylla cultivars which bloom on only old wood. Since this species is marginally stem hardy in zone 4, having the ability to bloom on new wood allows it to still flower in our climate even if the plant dies to the ground and needs to regrow from the base.

Continue reading "Getting Hydrangeas to Turn Blue" »

Cherry Prinsepia

Kathy Zuzek, University of Minnesota Extension Educator

Princepia Kathy ZuzekCherry prinsepia (Prinsepia sinensis) is a little known shrub native to Manchuria that has been in cultivation since 1896.  It is a member of the enormous Rosaceae family, and close relatives of prinsepia that  you may be familiar with are woody ornamental and fruit varieties from the genus Prunus (cherries, peaches, plums, apricots, almonds) and pearlbush (Exochorda serratifolia).

Cherry prinsepia is one of the first shrubs to leaf out in spring, providing some welcome color after a long Minnesota winter.  Bright green leaves are alternate on current season's growth but are produced in clusters on older wood.  A thorn is found at the base of each leaf or cluster of leaves.  The small immature leaves are soon masked by an explosion of light yellow 5-petaled flowers on old wood in late April.  In Minnesota, cherry prinsepia blooms at the same time as flowering almonds (Prunus triloba var. simplex).   

Continue reading "Cherry Prinsepia" »

August 1, 2009

Exploring the Potential for Large Leaved Rhododendrons for Minnesota

Laci High, University of Minnesota Graduate Student

PJM Rhododendron is well-adapted in Minnesota. David Zlesak

After a long, dreary Minnesotan winter, gardeners anticipate and appreciate the beauty of spring flowering shrubs such as rhododendrons and azaleas (genus Rhododendron) which can be the first sign of color in many landscapes.Due to its great soil adaptability and ease of cultivation compared to other members of the genus, PJM hybrids can be found along most residential streets in Minnesota.  These plants are loaded with lavender-pink flowers nestled among inconspicuous, scaly leaves.  Even though PJM hybrids have proven to be reliable performers for home gardeners, they lack the color range and glamorous trusses of broad-leafed forms typically found in more moderate climates.

Continue reading "Exploring the Potential for Large Leaved Rhododendrons for Minnesota" »

July 1, 2009

Drought-Tolerant Plants

Kathy Zuzek, University of Minnesota Extension Educator


Do you live in a geographic area with little rainfall? Do your sandy soils allow water to percolate away quickly? Are you looking for a drought-resistant landscape? Are attractive landscapes and water conservation both goals of yours? Below is a partial list of trees, shrubs, and herbaceous perennials that once established, grow well with little supplemental watering. Within most of the species listed, there are cultivar choices that will provide you with a wide variety of ornamental traits.

Continue reading "Drought-Tolerant Plants" »

Here Today Gone Tomorrow - spring leaf spot diseases make a short visit to Minnesota


Michelle Grabowski, University of Minnesota Extension Educator

For most areas of Minnesota, the spring of 2009 has been an unusually dry one.  This cool dry weather has kept many of the spring leaf spot diseases of trees at bay.  Diseases like anthracnose on oak, ash and maple have been absent up until the most recent wet weather.  Anthracnose is now being reported, especially in areas that received significant recent rain like southern Minnesota. The fungi that cause anthracnose, however, may not be causing problems for long. Anthracnose fungi thrive in cool wet weather and with the recent onset of hot temperatures, the growth and spread of this disease is likely to slow down.

Continue reading "Here Today Gone Tomorrow - spring leaf spot diseases make a short visit to Minnesota" »

It's Too Late To Treat Ash Now For EAB


Jeffrey Hahn, Asst. Extension Entomologist

With the discovery of emerald ash borer (EAB) in St. Paul in May, many people have been asking for information on how to protect their ash with insecticides.  While there are several options available to home residents within 15 miles of the infestation, the question people should be asking now is when should I treat my ash.  In general insecticide applications should be made from early May until early to mid-June.  With that in mind, it is really getting late to be treating your ash any longer this summer.

Photo 1: EAB galleries in infested tree in St. Paul. Jeff Hahn

It is possible that Tree-age (emamectin benzoate), which is a professional use only product, can be applied into July because its mode of action targets the larvae and not the adults.  However imidacloprid relies on being taken up by the tree into the canopy and killing adults that feed on leaves.  Because it takes three to four weeks for imidacloprid to be translocated in trees, any applications that take place now, will have little impact in protecting ash.  This is particularly true for products available to the general public.  If you are thinking of treating your ash yourself now, don’t do it.  You will be just wasting insecticides.  The next window of opportunity for insecticide applications will be this fall or next spring.

There are many factors to consider if you are thinking about treating your ash for EAB.  For more information on insecticide options for protecting ash from emerald ash borers, please see the EAB Insecticide Fact Sheet (pdf).

May 15, 2009

Emerald Ash Borer Discovered in Minnesota

In the last issue, we alerted you that emerald ash borer was a mile away from the Minnesota border. On May 14, the Minnesota Department of Agriculture confirmed that the pest has been located in St. Paul, Minnesota. Keep up with the latest news on Extension's emerald ash borer response page.

May 1, 2009

Emerald Ash Borer On Minnesota's Doorstep


Jeffrey Hahn, Asst. Extension Entomologist

Earlier this month, on April 7, Wisconsin reported a confirmed infestation of emerald ash borers (EAB) in the town of Victory.  This town is in Vernon county, about 20 miles south of La Crosse and on the banks of the Mississippi River about one mile from the Minnesota-Iowa border.  This the first time that EAB has been found in western Wisconsin.

The Minnesota Dept. of Agriculture has stepped up their surveillance efforts in Houston county which is right across the river from this infestation in Wisconsin.  So far, their surveys have not revealed any EAB.  Remember, that at this time, EAB has not been found in Minnesota (although the odds of finding it in Minnesota soon have gone dramatically up).  Because of the imminent danger of EAB, a quarantine has been put in place for Houston county, restricting the movement of ash trees, ash logs and branches, uncomposted wood chips, and any hardwood firewood.

Continue reading "Emerald Ash Borer On Minnesota's Doorstep" »

Simple Steps to Productive Apple Trees


Emily Tepe, University of Minnesota Research Fellow

Apples in the Home Garden

If you’ve ever dreamed about harvesting fresh fruit from your garden, apples are a great option. Sure, they require a bit more care than a typical landscape tree, but with a little TLC you could be harvesting juicy, crisp apples right from your own backyard!

There are a few things to keep in mind when growing apples that will help you achieve bountiful harvests of high quality fruit year after year. First it is important to know that apples require cross-pollination to reliably set fruit. This means planting more than one kind of apple tree. Your choice of varieties will largely depend on your priorities. If one tree will give you all the fruit you need you may want to consider planting a disease resistant flowering crab apple, such as Indian Summer or Snowdrift, for cross-pollination. Crabapples and edible apples can successfully cross pollinate. These trees are used in commercial orchards because they bloom over a longer period of time than most eating varieties, ensuring complete overlap of bloom. This equates to greater pollination potential of all the flowers, leading to more fruit. (Ensuring complete pollination and greatest fruit set might not be necessary however, which will be covered later when we talk about thinning.) These crabapple varieties and many others produce a profusion of flowers in the spring, and will then set an abundance of pretty, though inedible pea- to cherry-sized fruit which will dangle on the trees through the winter and into the next spring.  Since the tissue of the apple fruit that we eat is derived from cells of the maternal parent tree, the apple that serves as the pollinator will not affect our fruit quality.

Continue reading "Simple Steps to Productive Apple Trees" »

Distinguishing Disease from Winter Injury on Spruce Trees


Michelle Grabowski, University of Minnesota Extension Educator

Throughout Minnesota, purplish brown to rusty brown needles can be seen on spruce trees. A variety of problems can result in needle discoloration in spruces including insects, disease, and problems associated with environmental conditions. This time of year two common problems are Rhizosphaera needle cast and winter injury. Rhizosphaera needle cast is caused by a fungal pathogen. Winter injury is the result of environmental conditions. It is important to be able to distinguish between these two problems, since very different action is required to maintain tree health depending on the cause of the problem.

Rhizosphaera needle cast is caused by the fungi Rhizosphaera kalkhoffii and is most commonly seen on Colorado blue spruce, which are highly susceptible to the disease. White spruce and Norway spruce have greater resistance to the disease but can become infected when stressed. With the drought conditions present in Minnesota the last few summers, Rhizosphaera needle cast is showing up in a wide variety of spruce trees.

Continue reading "Distinguishing Disease from Winter Injury on Spruce Trees" »

Garden Calendar for May


Contributors: Michelle Grabowski and David C. Zlesak

May is a busy month with lots of gardening fun to be had.  After a long cold winter, the excitement of getting out and enjoying our gardens feels like a reward. 

Enjoy the many spring flowering shrubs (bridal wreath spirea, forsythia, lilacs, flowering almonds, etc.) and wait to prune them, if necessary, until after they are done flowering.  Pruning them before they flower would ultimately most benefit the plant because they wouldn’t be investing their stored energy in new growth that would soon be cut off.  However, after waiting this long for those beautiful flowers we don’t want to miss them! 

New growth is starting on most of our herbaceous perennials.  If one hasn’t cut back last year’s stems, now is a great time to do so before the new growth gets larger and interferes with removing the old growth.  Come spring, last years stems tend to be more brittle and tend to be easier to remove than last fall.  Many times pushing them a bit from side to side will allow them to cleanly snap at the base of the plant without even needing to physically cut them.

Continue reading "Garden Calendar for May" »

April 1, 2009

The Mystery of Maple Sap Flow

Stephen G. Saupe, Ph.D., College of St. Benedict/St. John’s University
Biology Department, Collegeville, MN 56321, (320)363–2782;


An annual springtime event from Maine to Minnesota is the production of maple syrup. Each spring, syrup-makers head to the woods to collect sap from the sugar maple tree (Acer saccharum Marsh.) and then cook it into one of nature’s greatest gifts. Although this ritual has been practiced for many years since its discovery by Native Americans, surprisingly the actual mechanism responsible for sap flow is still something of a botanical mystery. So, exactly what do scientists know about why sap drips out of a sugar maple tree in the spring? To answer this question we must first understand the conditions that affect the flow of maple sap, since our final explanation must account for these observations.

Continue reading "The Mystery of Maple Sap Flow" »

Golden Canker on Pagoda Dogwood

Michelle Grabowski, University of Minnesota Extension Educator


The word golden brings about images of wealth, vitality and prosperity. Unfortunately when this word is used to describe the branches of a pagoda dogwood, the connotation is quite the opposite. Golden canker is one of the most common diseases of pagoda dogwood small trees/large shrubs in Minnesota and it can be disfiguring and even deadly.

Photo 1: Yellow infected branch areas contrast sharply with purplish red healthy bark. Michelle Grabowski

In the early spring sunlight the infected branches are bright yellow to orange compared to the dark almost purplish red healthy bark. The striking contrast is almost pretty. Sadly any branch that has completely turned yellow is already dead and will not leaf out this spring. Close examination of these yellow branches will reveal that the branch is covered in tiny blister-like orange spots. A sharp line marks the border between healthy and diseased branch tissue.

Continue reading "Golden Canker on Pagoda Dogwood" »

Garden Calendar for April

calendar1_600.jpgStop pruning Oaks. April, May and June are considered high risk months for Oak Wilt infections. At this time the fungal pathogen is producing spores that can be carried by beetles from the Nitidulidae family. These beetles are sap feeders and will be attracted to fresh pruning cuts on oak trees.

Photo 1: Do not prune oak trees during April-June to avoid oak wilt infection. David Zlesak

There is still time to start seeds of fast growing warm season flower and vegetable species indoors for outdoor transplanting after danger of frost. These plants include: cosmos, marigolds, tomatoes, and zinnias. Cold hardy annuals can be direct seeded in the garden during April and include: calendula, sweet peas, peas, and larkspur. Cold hardy annual transplants we have started ourselves or purchased from the garden center can also be planted and include vegetables like cole crops (broccoli, cabbage, cauliflower, etc.) and flowers like pansies, snapdragons, and stocks.

Continue reading "Garden Calendar for April" »

March 1, 2009

What's Up With That?!

Michelle Grabowski

Salt is a common sight in Minnesota this time of year. Unfortunately sodium chloride from deicing salt can be very toxic to garden plants when in high concentrations. Evergreen needles, tree buds, tree roots and turfgrass can all be damaged or killed by deicing salt splashing onto above ground plant parts or washing into the soil around plant roots. In addition when de icing salt washes into our lakes and rivers with spring snow melt, it reduces water quality and could harm aquatic wildlife.

What can a Minnesotan do?

Prevent future problems by reducing use of deicing salt

  • Shovel snow soon after snowfall to avoid compaction and ice formation.
  • Redirect downspouts so that water flows away from walkways.
  • Use the least amount of salt necessary to break up the ice. Then use a shovel to clear the sidewalk.
  • Reduce the amount of salt needed by mixing sand or gravel with a small amount of salt to provide traction on ice.
  • Use non sodium chloride deicing salts like CMA or other acetate de-icers which are less toxic to plants.

If plant damage does occur, water plants liberally in the spring to flush the salt out of the soil. Next year use the steps above to prevent future damage.

In the Rhododendron Fairyland: The Fantasy of Alpines


The prominent 19th century English botanist, Francis Kingdon-Ward, wrote manuscripts in great detail profiling his lifelong collection of high-altitude ornamental plants. Throughout his lifetime, Kingdon-Ward scavenged the Namcha Barwa Mountain crevices and the Tsangpo River Gorge for these select alpine plants during his some 65 explorations through the southeast of Tibet. These rare plants became the gems of his world-famous collection and ultimately, became his lasting legacy. Perhaps, the modern gardener's intrigue for alpine plants can be traced back to Kingdon-Ward's evocative descriptions of these beautifully rare plants. In any case, the botanical world has developed a great fascination for these charming ornamentals. Our fascination is firmly rooted in the marvel of botanical life that is capable of inhabiting and thriving on the so-called "Rooftop of the World."

Continue reading "In the Rhododendron Fairyland: The Fantasy of Alpines" »

February 1, 2009

What's Up With That?!

David C. Zlesak

wuwt_600px.jpg“Oh no, are my rhododendrons dying?” or something similar is a startling thought that comes to mind the first time many of us see this characteristic curling on leaves of our rhododendrons in winter. Fortunately, this is a normal response called thermonasty that actually helps our rhododendrons survive this difficult time of year. This curling and drooping of the foliage is in response to cold temperatures (thermo= heat or temperature and nasty= movement to a stimulus that is non-directional). As temperatures warm and cool during winter we can actually observe rhododendron leaves appearing less or more drooped and curled. As a broadleaf evergreen, the large surface area of rhododendron leaves makes them especially vulnerable to drying out during the winter. With the frozen soil this time of year, additional water cannot easily move up the plant and replace what evaporates from the foliage. Curling and drooping to prevent wind from reaching the undersides of the leaves, where stomates (openings for gas exchange) are typically more concentrated, can help prevent wind from drawing out as much moisture. In addition, many rhododendrons are native understory plants in deciduous forests. During the growing season the plants are shaded by the trees above, but during the winter when plants cannot utilize light well, leaves typically experience more intense sunlight capable of damaging exposed leaf tissue. Curling and drooping also aids the plant by reducing the overall amount of light intercepting a leaf. As we are excited for spring to come by this time of year in Minnesota, it might be fun for us as gardeners to look to our rhododendrons for a light hearted way to predict how much more winter we have left than groundhogs and how afraid they are of their shadows!

The Winter View

Kathy Zuzek, University of Minnesota Extension Educator

art1-1_800px.jpgIt’s official. Winter is more than half over. Are you feeling a bit desperate for warm temperatures and the color green? I spend every February dreaming of a trip to anywhere warm and green or of a kinder, gentler Minnesota where spring actually arrives in February. A quick look out of my window though always reminds me of how truly bleak our long winters would be without woody plants.

Continue reading "The Winter View" »

Remove Fire Blight Cankers Now to Avoid Disease Problems in the Spring

Michelle Grabowski, University of Minnesota Extension Educator

Photo 1: Fire blight canker on a young apple branch. Michelle Grabowski

This past summer, many Minnesotans noticed dead brown wilted leaves on apple, crabapple and mountain ash trees caused by the bacterial disease known as fire blight (Read Midsummer Trouble for Trees & Shrubs) Although symptoms of fire blight are most apparent in spring and summer months, one of the best times to manage this disease is right now.

Continue reading "Remove Fire Blight Cankers Now to Avoid Disease Problems in the Spring" »

January 1, 2009

What's Up With That?!


David C. Zlelsak

As eastern white pines (Pinus strobus) mature, they tend to develop a rounded upper canopy and interesting asymmetric form to their branches. The interesting branch arrangement, providing rich character to these trees, is due in part to how they have adapted to handle the stress imposed by the weight of snow and ice. The generally horizontal branches of white pine are somewhat brittle, and as they become excessively weighted down, especially in the presence of heavy winds, they respond by snapping and collapsing to the ground. The straight trunk typically remains in tact, helping to keep the tree standing tall. It’s impressive to see forests in Minnesota and Wisconsin where mature eastern white pines typically tower over neighboring tree species.

Photo 1: David Zlesak

Tree Care Advisor Core Course 2009


Mark your calendars for the 2009 Tree Care Advisor Core Course in St. Paul, Minnesota! Training includes education on several topics including: tree identification, plant selection, basic physiology and morphology, soils, site analysis, firewood identification, diagnosis of disease and insect problems, pruning, planting and more. These trainings are geared towards individuals who may not know much about trees but do know they want to learn.

Continue reading "Tree Care Advisor Core Course 2009" »