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December 2011 Archives

What to Do about Pot-Bound Plants

em>By Jeff Gillman, Associate Professor - Department of Horticultural Science

So you've just bought a pot-bound plant and you don't know what to do? Gary Johnson, Chad Giblin and I have been testing various techniques to get trees out of their pot-bound states for the last 8 years or so, and here are some of the things that we've found.

The number one problem with planting a pot-bound tree is that they are usually planted too deeply. Trees in containers often have three inches between their uppermost roots and the soil line -- or even more! When a tree like this is transplanted into a landscape without having its planting height adjusted, the roots circling near the top of the container will eventually press up against the stem of the tree and strangle it to death (photo 1).

Jeff Gillman

Photo 1: Pot bound plant's root system 5 years after planting; tree was planted too deep based on media level in pot

When planting a container grown tree make sure that the first large root connecting to the stem (usually about ¼ inch in diameter) is visible after you fill in the planting hole. This will ensure that as the tree gets older and roots and stems expand there will be no compression of the stem.

Roots do not continue to grow in a circle after a tree is planted, even in severely pot-bound plants. Roots which were already circling in a pot-bound plant when the plant was transplanted will not straighten out after planting, but as the roots grow they will grow outwards, not in a circle (photo 1). Right now, with the research we currently have, it is not clear how circling roots will affect a tree if they are only present below the stem. Yes, they look ugly, but looking ugly doesn't mean they're not doing their job.

Most of the common techniques that the extension service recommends for pot-bound trees will not really do that much. Scoring the sides of pot-bound root balls with a razor knife or butterflying the root ball with a shovel just doesn't work that well. If you're really serious about not having any circling roots then you need to use a technique called a box cut. A box cut is performed by cutting the root ball into the shape of a box by using a pruning saw (photo 2).

Jeff Gillman

Photo 2: Box cut on potted arborvitae

Root balls treated using the box cut method generally had good looking root systems after 5 years in the ground (Photo 3). Circling roots were drastically reduced, but not entirely eliminated.

Jeff Gillman

Photo 3: Box cut plant 5 years after planting


In terms of what we're actually recommending -- Right now we are recommending that you check the planting depth of all container grown plants before planting. Only in rare cases do we think that you'll find them planted at the proper depth. After removing the media from the top of the root ball to correct planting depth look for circling roots. If you don't see any circling roots thicker than a pencil then it probably isn't worth your time to do anything besides planting the tree, being careful to make sure that the uppermost root is planted at the soil surface. However, if you see any circling roots with a diameter greater than a pencil, we recommend using a box cut on the root ball.

On a final note, none of the trees we purchase ever need to be pot-bound. There are many different containers out there that will all but eliminate circling roots, such as Smart Pots, Superoots, and Root Trappers (photo 4). If we demand that companies provide trees planted in these containers then, someday soon, we may never need to worry about circling roots again.

Jeff Gillman

Photo 4: Root Trapper Pot


Contents: December 1, 2011

What is the true cost of planting a tree too deep?

Karl Foord, UMN Extension Educator

Karl Foord

Photo 1: Encircling root has significantly stunted this tree.

If you purchased a tree and planted it at the soil line as it was in the pot, it is likely that this tree was planted too deep - with drastic consequences. Research conducted by Gary Johnson, Jeff Gillman, and Chad Giblin has shown that trees planted too deeply tend to generate roots that can strangle the plant. Dr. Jeff Gillman explains more of the science in the following article; however in this article I want to address what I believe is the true cost of making such an error.


Karl Foord

I have two 'Autumn Blaze' maple trees that were planted approximately 10 years ago. Several years ago I checked the planting depth of the trees and discovered that one had been planted too deep (tree 1). Tree 1 had several encircling roots that severely impacted its growth (Photo 1). Tree 2 had a few encircling roots that I caught before much damage was done (Photo 2). What is the result? The trunk diameter of tree 1 is 4" and the trunk diameter of tree 2 is 8". Tree 1 is @ 25' tall and tree 2 is @ 35' tall. Tree 1's leaves colored and dropped early. Tree 1 looks anemic next to tree 2, and I have concerns as to whether it will survive.

What is the true cost of this error? TIME! If this tree dies and needs to be replaced, it will be some 11 or 12 years behind the other trees. Even if it lives, it is essentially half the size of a tree planted at the same time. All for having planted the tree in the ground at the soil level as it was in the pot; a fairly reasonable assumption all things considered. I can buy another tree but I cannot gain back the 12 years. Plant your trees at the correct depth as noted in Dr. Gillman's article.

Bur Oak Blight

Michelle Grabowski, UMN Extension Educator

T. Harrington, ISU

Photo 1: Leaves killed by Bur Oak Blight clinging to the tree after fall leaf drop

A healthy bur oak will drop all of it's leaves in the fall. Leaves that are infected with the fungal pathogen (Tubakia sp.) that causes Bur Oak Blight (BOB) remain attached to the tree into the winter. As a result, now is a good time to examine landscape bur oaks for possible infection with BOB.


Bur Oak Blight causes leaves of bur oak trees to develop brown wedge shaped lesions in July and August. This fungal disease often starts in the lower canopy and progresses up the tree in following years. Some bur oak trees are highly susceptible to BOB. After several years of infection, the entire canopy can appear brown and scorched. These severely infected trees are weakened and often fall prey to secondary pests like two lined chestnut borer and Armillaria root rot. It is possible for bur oaks to be killed by this combination of fungal and insect attackers.

Bur Oak Blight was first identified in Minnesota in 2010. Since then BOB has been found in 20 Minnesota counties including Mille Lacs, Sherburne, Hennepin, Ramsey, Washington, Anoka, Wright, Dakota, Carver, Pennington, Beltrami, Pope, Lac Qui Parle, Ottertail, Stearns, Polk, Marshall, Mower, McLeod, and Morrison.

If you suspect your bur oak tree is infected with BOB, contact the University of Minnesota Plant Disease Clinic about how to submit a sample for diagnosis. For more information about BOB, read the USDA Forest Service Pest Alert about BOB.

Winter Squash: Easy to Grow and Good for You

Mary H. Meyer, University of Minnesota Professor and Extension Horticulturist

Image Source's Name

Squash and pumpkins can store for several months, if harvested at maturity and properly cured. (Click to enlarge.)

I love winter squash! So with the more than 100 kinds grown at the Arboretum this past summer, it was fun looking at the huge variety and deciding which ones I would try cooking this winter. I settled on 8 'new-to-me' kinds: orange hubbard, fairytale pumpkin, autumn crown, Queensland blue, marina di chioggia, rouge vif d'etampes or cinderella pumpkin, crown, large world of color blend, and 1 'old' favorite: blue hubbard, see photo below. You can still find winter squash at the markets and you can make plans this winter to grow your own squash next summer. Winter squash are easy to grow, have high nutritional value, and some kinds store well for several months. If you can still find open Farmer's Markets, you will likely have a much better selection of squash and pumpkins than the one or two kinds available in the supermarket.

Pumpkin and winter squash were cultivated by the American Indians for centuries and are native to North America. Pumpkin is derived from the French word pampion meaning "sun-baked squash", which was modified to pompkin and finally to pumpkin.

What is the difference between a pumpkin and squash?

The scientific name of most pumpkins, and acorn, delicata, and spaghetti squash is Cucurbita pepo; these fruits have very hard stems or petioles, which cannot be dented with your fingernail.

Winter squash usually has a softer, wider, pulpy stem or petiole, which you can penetrate with your fingernail. Most of the large fruited types, the HUGE award winners, 'Boston Marrow' and 'Mammoth' are Cucurbita maxima, along with many kinds including buttercup, kabocha and hubbard squash.

The third species is the buff-colored butternut squash, these oblong beige fruits are Cucurbita moschata, and are excellent for baking and pies. This species is usually sold as canned pumpkin.

Mary Meyer

The 2011 pumpkin and squash display in the Great Hall at the Minnesota Landscape Arboretum.

Although all kinds of pumpkin and squash are edible, they vary in consistency, texture, color, and flavor. Some may have flesh that is several inches thick with a small seed cavity, while others are thin fleshed with large seed cavities, making them inefficient to process and bake.

What squash or pumpkin is best to grow in Minnesota?

Most winter squash and pumpkins can be grown and mature successfully in Minnesota, especially central and southern areas. In general, the larger the fruit, the longer the growing season required. Any variety that matures in 100 days or less should produce mature fruit in Minnesota. Varieties that need 120 days will likely be successful only in the southern portion of the state. Most are direct seeded in the field. It is important to know the days to harvest for the varieties you are considering.

Winter squash require full sun, plenty of space for their long vines, and adequate moisture. After growing to maturity on the vine, harvest fruit before any injury from frost. Although appearing to be tough and firm, all curcurbits are tropical plants and do not do well in cool or cold weather; frost can damage the fruit and prevent the rind from curing properly and long storage.

After harvest, clean the rind with a soft cloth to remove any soil. Store the fruit at 80° to 85°F with 75 to 80% relative humidity for approximately 10 days to cure the fruit. Curing heals wounds, helps ripen immature fruit, enhances color, and insures a longer post-harvest life. Curing is beneficial in pumpkins and some winter squash, but 'Butternut,' 'Hubbard,' and 'Quality' squashes have not shown any added benefits from curing. Curing is detrimental in Acorn types, and will hasten senescence. After curing, the fruit can be stored at 50-55 degrees but no cooler, and it can be held at room temperature if 50-55 is not possible. Store cut pieces in the refrigerator.

Immature fruit will not fully develop indoors. Fruit that is mature green, may ripen further indoors but will not have as high nutritional value, or flavor. Color change is often important, as most squash and pumpkins turn from green to orange, beige, blue, pink or yellow, at maturity.

Nutrition and Cooking

While all squash and pumpkins are edible, some have more sugar and flavor. If the fruit is fully mature, it will remain firm and can actually improve in storage, for 3 to even 6 months, if the rind has been cured properly and is not bruised. Acorn squash is an exception; it is not a 'good keeper' and should be used within a month of harvest. Cucurbita pepo, true pumpkins, acorn and spaghetti squash have long fibers and some cooks prefer winter squash because they are non-fibrous. Regardless of the type, cooking is similar for all squash or pumpkins, however, the large ones are much more difficult to handle and peel. By far the easiest way is simply by cutting the fruit in half, removing the seeds and baking it cut side down. Rubbing the edges with olive oil, or butter prevents adhering to the pan.

Winter squash is a good source of complex carbohydrates and fiber. Research suggests that the soluble fiber in foods such as squash can play an important role in reducing colon cancer. Winter squash is also a source of potassium, niacin, iron and beta carotene. Usually, the darker the orange color, the higher the beta carotene content. Beta carotene is converted to Vitamin A, which is essential for healthy skin, vision, and bone development. The nutrient content of winter squash can vary, depending on the variety, maturity and condition of the fruit. The following information is a summary of all varieties, cooked, baked and cubed:

Nutrition Facts (1 cup cooked, cubed)
Calories 80
Protein 1.8 grams
Carbohydrate 18 grams
Dietary Fiber 5.8 grams
Calcium 28.7 mg
Iron 0.67 mg
Potassium 895 mg
Folate 57 mcg
Vitamin A 7,291.85 units

I have vine borers in my squash, how can I control them?

Vine borers are difficult to control effectively with insecticides. You can reduce potential damage the following season by disposing of infested plants. Vining types of squash can be encouraged to root at the nodes, giving the plant some ability to withstand attacks of vine borers. Some success in control of an active infestation may be achieved by carefully splitting open areas being fed upon and removing the larvae. Late planting of short maturing squash, planting after July 1, after which the adult has laid its eggs, may avoid borer damage.

References:
Minnesota: http://www.extension.umn.edu/distribution/horticulture/m1264.html
North Carolina State: http://www.ces.ncsu.edu/depts/hort/hil/hil-24.html
Alabama: http://www.aces.edu/pubs/docs/A/ANR-1041/ANR-1041.pdf
Illinois: http://urbanext.illinois.edu/veggies/wsquash.cfm
A beautiful book on squash: Goldman, A. 2004. The Compleat Squash: A Passionate Grower's Guide to Pumpkins, Squashes, and Gourds. Workman Publishing.

Karl Foord, UMN Extension Educator

I often see recommendations to use the pesticide with the least impact when controlling pests. However, prior to spraying every effort should be made to avoid pest outbreaks by using the best management practices for a particular crop. For example, most fungi need a period of wetness for their spores to germinate. Managing systems to permit maximum airflow reduces drying time on leaves and reduces the opportunities for fungal spores to germinate.

For the purposes of this article let's assume that all best efforts were made and a spray as the last resort was required. How would you go about choosing the one with the least impact? The first question might be impact on whom, with the second being how one would measure such impact. At a University of California Davis website a series of pesticides is listed. Each pesticide is rated according to its impact on aquatic live, beneficial insects, honeybees, and humans. The human impact is separated into acute and long term impacts. Acute being what can happen to you today, and long term being what can happen over a number of years due to continued exposure at lower dosage rates.

Each chemical is given a potential hazard rating based on a series of other documents and warnings on the chemical's label. These are complicated but can be accessed at the website previously mentioned. The ratings range from no risk, no known risk, and very low risk to very high risk or no data available. For those pesticides labeled for strawberry, the impact information has been consolidated into a table where the materials have been ranked from lowest risk to those of highest risk (table 1). For example if you encountered slugs (mollusks) in your strawberries, the less impactful of the two active ingredients would be iron phosphate and not metaldehyde. So looking for a product with this as the active ingredient would be the first choice.

If you encountered tarnished plant bug in your strawberries, you would want to choose an insecticidal soap as a first choice over malathion. If you were forced to go to malathion you would realize that you would want to avoid any situation where the spray could get into surface water. You would also want to be particularly sensitive beneficial insects and honeybee pollinators and not spray when they are active, most likely after dark.

This table should permit you to select the least impactful chemical, and to apply it in a manner producing the least impact through an understanding what organisms were at risk from the application.

Karl Foord

Moth Flies in Homes

Jeffrey Hahn, Assistant Extension Entomologist

Jeff Hahn

Photo 1: Moth fly

Not all small-sized flies that are found in homes are necessarily fruit flies. Another common type are moth flies, also called drain flies. These flies are about 1/8th inch long (or a little less) and are dark-colored with many hairs which gives them a fuzzy, moth-like appearance. They have leaf-shaped wings that are often held roof-like over their bodies (they are sometimes also held flat). If you look closely, you may be able to many parallel longitudinal veins in the wings.

Moth flies can be present anywhere in a home, especially in bathrooms, basements, and kitchens. These flies lay their eggs in moist, organic matter where the larvae, small, slender, legless insects, feed on decaying organic matter, fungi, algae, and similar material. They are commonly found associated with the gelatinous film found in sinks, shower and bathtub drains, and similar places. Moths flies can also be associated with sewage from sewer line breaks. Moth flies are primarily a nuisance because of their presence. They don't bite people but they can potentially be a mechanical vector of disease because of their association with filth.

The best control of moth flies is to remove the source of the infestation. You can not eliminate a problem by just spraying the adults that are out in the open, First check drains and basins for the presence of an infestation. If you are not sure, place some tape over the openings (sticky side down); flies will get stuck on the tape as they try to fly out. If you suspect a sewer line break under a floor or slab, it may be necessary to break through the floor or concrete to verify this.

If you are dealing with a drain, you need to remove the gelatinous gunk that has accumulated. You can do that by taking a brush with stiff bristles and physically removing it. Another effective option is to use biological drain cleaner which breaks down and removes he organic material. However the use of hot/boiling water, bleach, and chemical drain cleaners is not effective. Attempts to try to drown the larvae is difficult and is unlikely to be successful. If you are dealing with sewage from a broken pipe, it is critical to fix the break and remove the sewage and any contaminated soil that is present.

Calendar: December 1, 2011

Photo by Scott Bauer, K7244-16

Poinsettias are among the easiest holiday plants to grow. First, you must choose a healthy one, and get it home without suffering any cold damage. It should be wrapped well, then transported in a heated vehicle, not left in the car while you do other shopping. Cut the bottom of the decorative pot covering so excess water drains out, and place the poinsettia in a bright, sunny location. Water thoroughly when the soil surface begins to dry, and then fertilize monthly after four to six weeks. The U of M Extension has a great publication available for more information on the care of poinsettias.

Don't hesitate to buy a fresh Minnesota-grown Christmas tree. They're a renewable crop produced on marginal agricultural land. As trees are harvested, others are planted for future sales. While they grow, conifers reduce soil erosion and provide habitat for wildlife. Once you get the tree home, cut an inch or so off it's base, then set it immediately in a stand that holds plenty of water. No additives are needed; just make sure the water doesn't run out. The Minnesota Christmas Tree Association has more information about how to find a farm near you.

Bridget Barton

The St. Paul Campus of the U of M in the winter.

The best way to keep icy sidewalks, steps and driveways sage without damaging nearby plants is to rely primarily on sand or grit, rather than de-icing products. If necessary, mix a small amount of deicer or lawn fertilizer into the sand. The fertilizer or deicer will run off eventually, and accumulates in the soil. The more you use over the winter, the more likely that plants will be burned be deicer or fertilizer salts.

Happy holidays from your friends at the Yard and Garden News! Have a safe and merry month, and we will see you in the new year.

Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton

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