Wrapping trees for winter protection is not an attempt to keep them ‘warm’ but has the objective to prevent or minimize three sources of winter damage: from desiccating winds, sunscald, and gnawing rodents. Even if the trees in the landscape have survived previous winters unscathed, a wise horticulturist would not try to stretch this luck too far. Winters in ND, SD, and MN are so unpredicatble and variable that even well-established plantings can get hit hard when least expected.

 Protection from Desiccating Winds:

Don’t wrap evergreen trees like a Christmas present with burlap. That has the potential to create more problems than it solves by eliminating too much light and packing the branches too closely together, which often breeds disease problems before the covering gets taken off in the spring. Instead opt for a buffer against the wind and direct sunshine on newly planted or smaller evergreens in this fashion:

This burlap barrier would be oriented to buffer the winds and direct sunshine from the west or southwest, yet still allow the top to get sufficient sunlight and air. Using anti-desiccants have not proven to be effective in this, in spite of the fact they are still promoted and used by homeowners and professionals alike. The anti-desiccants simply do not have the staying power needed to see them through the long winter months.

Protection from Sunscald:

This is really an incorrect term as the sun doesn’t actually ‘scald’ the trunk or bark of the tree. Common on newly or recently planted trees, it shows up on the west or southwest side of the thin-barked trees the spring following the winter months. On cold winter days, the sun can heat up bark to the point where cambial activity is stimulated. When the sun is blocked by a cloud, hill, or building, bark temperature drops rapidly, killing the active tissue. The result is something like this:

The sketch on the left shows the damage caused which will heal slowly if at all, while the sketch on the right shows the wound cleaned up by cutting the loosened and damaged bark back to where it is attached to the trunk cylinder. From there, normal healing will begin taking place at the start of the growing season.

Rodent Damage:

Rabbits and voles are the major perpetrators of this damage. Rabbits can walk across the top of snow cover and nibble branches and girdle the trunk. Voles will work on the trunks of trees under the snow. The tree should be wrapped with either Kraft paper or hardware cloth up to the first branch, and from that point up, the branches sprayed with a repellant like Liquid Fence or Plantskydd. Both will also protect against deer damage in rural areas. Wrapping in this manner will also protect the trees from sunscald.

By being a little proactive in care for your woody plants, ND’s severe winters need not be a major concern. Little things can make a difference from one season to another, such as microclimate. If a particular tree or shrub just doesn’t come through the winter in a particular location no matter what care is provided, consider a relocation on your property where slight climatic conditions may make a difference.

Ron Smith, Ph.D.   
Horticulturist and Turfgrass Specialist
ISA Certified Arborist

We all know that it is normal for deciduous tree leaves to change color and drop at this time of year. What doesn’t seem to be understood by many people is that “evergreens” drop their needles at this time as well. Not as colorfully, but they are dropped none-the-less.

Here is a photo, courtesy of the US Forest Service – showing what is considered a “normal” needle drop at this time of year on a pine.

Note that the yellowing of the needles is confined to the older material; the current season’s growth is normal and healthy appearing. Consequently, evergreens have a “needle life-span” that is roughly unique to each species. Leaf life-span is the age when leaves are shed from a plant. In conifers this includes leaves with acicular (needle-like), awl-like, and scale-like forms. Two extreme examples of leaf life-span differences are larches and bristle cone pine. Larches are deciduous conifers that retain needles for 5 to 6 months (a growing season) and shed them annually. In contrast, needles exceeding 40-years old have been documented on bristlecone pine. Typically, bristle cone pine trees retain needles for approximately 15 years, rather than the maximum 40 year plus extreme. Other examples between these extremes include spruce (5-7 years), Douglas-fi r (4-8 years), and white pine (2-3 years). Leaf lifespan varies between conifer genera (i.e., spruces, pines, firs, larches, etc.) and species within a genera.

Needle drop will vary from year to year with the same evergreen: extremely dry weather will cause the drop to occur a little ahead of schedule and in a grand fashion (all at once, or so it appears) while in normal growing seasons, the needle drop may be very little or held off until the following spring.

I encourage homeowners to make a ‘sport’ of this; start with this year recording the date that needle drop is observed and whether or not it is heavy, normal, or minimal, and see how this data varies from year to year.

- Ron Smith, NDSU Horticulturist and Turfgrass Specialist, ISA Certified Arborist

With fall ‘officially’ here, questions have been coming in concerning dividing perennials. As a sweeping generalization, they should be divided in the season opposite their flowering time. This means spring flowering plants should be divided in the fall and fall bearing plants in the spring. Many summer blooming plants can be divided in either the fall or spring. This allows for maximum energy utilization for foliage and root production, with the result being healthier and showier flowers the following season.

Here is a short list of some herbaceous perennials that can be divided at this time of year:

Achillea x ‘Coronation Gold’ – now or in the early spring

Ajuga reptans

Cersastium tomentosum

Dicentra spectabilis

Hemerocallis species

Hosta species

Paeonia lactiflora

Phlox paniculata

Of course, if the need arises to move or divide any herbaceous perennial, then do it irregardless of the season of bloom. Gardeners would rather attempt to save a favorite plant than to know doing nothing will spell its doom.

- Ron Smith, NDSU Horticulturist and Turfgrass Specialist, ISA Certified Arborist

(Pictured: "Hosta", Ian BC North,available under a Creative Commons Attribution-NonCommericial 2.0 license)

NDSU Extension has posted a new video on caring for your lawn and tress after floodwaters have receded. Extension Forester Joe Zeleznik and NDSU Extension Horticulture Specialist Tom Kalb inspect a park that had been flooded in Minot, ND and give advice on what to do next.

Watch it now.

Apples being eaten by birds and squirrels; melons, pumpkins, and squash being ravaged by rodents –rabbits, voles, raccoons, whatever!! They in essence, are getting to your garden crop before you do!

Stop waiting for a hard or killing frost to harvest your apples and other produce from the garden It is September 21,  and 90% of the edible stuff in your garden is at, or close to its peak of ripeness. Better to get everything harvested rather than lose a significant amount to the wildlife roaming around your property.

Apples and melons are climacteric fruits and will continue to ripen after harvest. If you place them in a bag with a ripe peach or banana where ethylene is generated, the ripening will be accelerated. It is better to get something out of your garden a little under-ripe than to lose it all to nature’s interlopers!!

(Photo courtesy Flickr user chedder)

- Ron Smith, NDSU Horticulturist and Turfgrass Specialist, ISA Certified Arborist

“Are my tomatoes going to survive?” “Will my pumpkins and winter squash be damaged by the cold temperatures”?  “Are my plums and apples safe from frost damage”?

These and other similar questions are all too familiar with the first threats of universal frosts across the region. Generally, tomatoes and peppers are the ones that will be most adversely affected, and should be covered with a protective cotton sheet, tarp, newspaper tents, or an old blanket. Fruit trees like plum and apple will have pretty much a built-in protection assuming they are still carrying a fully foliated canopy. The leaves will act as protectants from temperatures that might dip into the lower 30’s or upper 20’s for a short period overnight. That, along with the sugars present in these fruits, will offer protection from these initial frost events. Not for long, however! As the trees defoliate, and these events occur with greater frequency, with increasingly lower temperatures, damage potential increases, and the best efforts to protect tomatoes and peppers will become futile exercises. Best Bet: harvest everything that is mature to ripen indoors.

Many pumpkins are still green at this date. They will not “yellow-up” if the vine has been killed by the low temperatures. They will stay green and simply rot thereafter. Root crops like carrots will handle the fall frosts with no problems; cabbage and lettuce likewise, until the temperature goes below 28 degrees F. for an extended period.

Likely damaged by light frost: Beans, cucumbers, eggplants, muskmelon, New Zealand spinach, okra, peppers, pumpkins, summer squash, sweet corn, tomatoes, watermelon, amaranth, and winter squash (plants).

Can withstand light frost: Artichokes, beets, carrots, cauliflower, celery, chinese cabbage, endive, lettuce, parsnips, peas, swiss chard, escarole, arugula, bok choy, mache, and radicchio.

Can withstand hard frost: Broccoli, Brussels sprouts, cabbage, collards, kale, kohlrabi, mustard, onions, parsley, peas, radishes, spinach, turnips, leeks, and sorrel.

It is important to understand that temperature is not the only factor affecting survivorship of plants during a frost event. The further a plant or its parts are from the ground, the more likely it is to be damaged by frost. The ground is usually still warm in early fall and will radiate some warmth to plants that are close to the ground. Humidity can also help protect plants from frost. Humid air holds more heat and reduces the drying effects of frost. Air movement also has an influence on frost damage. When wind blows during cold nights, it sweeps away any warm air trapped near structures or the ground, eliminating their insulating capabilities.

Tender plants can be protected from a few light frosts with row covers or blankets. Mulched beets, carrots, leeks, onions, radishes, and parsnips can be harvested later in fall before the ground freezes. Light frost makes leafy greens and root vegetables sweeter, so it's worth leaving some of your kale and carrots in the ground until you're ready to use them.

Ron Smith, PhD, Extension Horticulturist

Last weekend I was looking at apple trees near Detroit Lakes, Minnesota.  On one tree I noticed tiny caterpillars swarming the tips of two branches (Figure 1).  I also found egg masses on those same branches.  The larvae are forest tent caterpillar (Malacosoma disstria).  The mature larvae of forest tent caterpillar are easy to distinguish by the white, keyhole-shaped markings along their top sides (Figure 2).  The young larvae in Figure 1 don’t show those markings yet, though three days later, they are beginning to develop.

Controlling the insect was incredibly easy in this case – I clipped the ends off of three branches, removing the larvae and the egg masses (Figure 3).  However, if the infestation had been heavy, chemical control may have become necessary.  In such situations, Bt works well to control young caterpillars, while permethrin or pyrethrins or other insecticides are needed for older larvae.  As always, when using pesticides, follow label instructions carefully.

Figure 3. Egg mass of forest tent caterpillar

Once established, rhubarb plants will tend to produce seed stalks, flowers, and seeds each season. Cut the stalks as soon as the large pods appear at the base to allow energy to go into producing new leaves. If your rhubarb plant doesn’t produce seed stalks, don’t worry – it will eventually.

For more information on growing rhubarb, check out the NDSU Extension Service publication, "Asparagus and Rhubarb (PDF) ."

(Photo courtesy Satrina0)