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How To Winterize Trees & Shrubs

Plants and trees experience life cycles through seasons unlike human beings, whose life cycles occur every day. We require a certain amount of nutrients, water, and rest each day. The amount and quality of our rest helps to determine how healthy and productive we are. The same can be said for plants. Most trees “sleep” each winter (called their dormancy period). The amount and quality of their rest also determines their health and productivity!

Let’s discuss preparation for winter, the challenges you may face, and making this dormancy period the best it can be for your plants and trees.

Winter Challenges

Extreme cold isn't the only challenge faced by woody plants; in fact, plants hardy to your region should endure normal winter temperatures just fine. However, winter can wreak havoc in other ways.

  • Early cold spells can damage plant tissues that haven't had a chance to harden off for the winter.
  • Dry winds and winter sun can dry out or "burn" conifer needles and broadleaf evergreen foliage, which continue to transpire (give off water vapor) during winter.
  • Frozen soil means plants can't take up water to replace the moisture lost from evaporation and transpiration.
  • Midwinter thaws can "fool" plants into breaking dormancy too early, and the tender new growth may be killed by the next cold snap.
  • Alternating freeze/thaw cycles can heave new plants out of the ground, leaving roots exposed to drying wind and sun.
  • Bright winter sun heats up dark tree bark, which can freeze and crack when temperatures drop quickly at sunset.
  • Deer, mice, rabbits and other animals gnaw bark and browse leaves and twigs when other food becomes scarce during long, cold winters.

Although wet, heavy snow can damage branches, snow cover is usually good for plants. A layer of snow provides moisture and helps insulate the soil and roots from fluctuating temperatures.

Preparing for the Big Chill

Healthy plants are more likely to get through winter unscathed. A plant that has struggled during the growing season, whether due to insufficient sunlight, water or nutrients, or heavy damage from insects or disease, will enter winter in a vulnerable state. Start your winter-protection strategy with careful care during the growing season and into autumn.

  • Don't prune after midsummer. Pruning stimulates tender, new growth and delays dormancy.
  • Stop fertilizing plants six weeks before the first fall frost, to help plants harden off properly.
  • Water plants thoroughly throughout fall until the ground freezes; make sure the water penetrates 12" to 18" deep to reach the root zone. Young or newly planted trees will require more attention because of limited abilities in obtaining water in their growing environment. The key to survival is giving trees adequate moisture before winter freezes the world around them. 

Outdoor Plants and Trees

Insulation
It is important to protect the root systems of young plants and trees. This can easily be achieved by applying a layer of mulch on top of the soil around the root system. Mulch, which can be comprised of natural things like wood chips, leaf/yard compost, sawdust, or straw, acts as an insulator that protects the roots when the temperature drops in late fall/winter/early spring. Mulch also acts as a weed deterrent and helps retain moisture during the growing season. Laying down a weed-mat barrier and covering the barrier with mulch is a simple means to avoid a number of problems at the root level all year long.

 

Tree Wraps
As summer ends, the grass and ground-covers toughen, moving rabbits to chew on tree bark. This destructive threat increases with cold weather and snow cover. On the farm, outbuildings, clutter and ground-cover provide adequate cover to house this animal. In urban settings, landscaping, hedges, and ground-cover provide the same housing and can be even worse than the rural setting. It’s heartbreaking to grow and nurture plants and trees along, only to wake one morning to find them girdled to death or impaired for life by hungry critters. Rabbits can chew trees way up into their fifth and sixth season. Simple and inexpensive solutions that can be applied in mere seconds are tree wraps.

These wraps also protect the trunk against sun scald and frost cracks due to the temperature fluctuations from sun exposure in the winter. Most winter damage to the tree’s trunk is from getting warmed up on sunny winter days and then chilled quickly at nightfall. The trunk often doesn’t adjust to the sudden temperature drop. The wounds caused by temperature fluctuations can leave the tree exposed to fungal organisms, which cause decay in the tree. Prevention includes guarding the trunks of younger and smooth-bark trees up to about the first branches using a flexible, tree wrap. Leave the wrap on until after the last freezing temperatures. Remove tree guards in the spring to reduce potential damage from disease and insects. 

Cracking can occur on smooth-bark trees during the winter months.

Protect fruit and shade trees against sun scald, moisture loss and insect damage.

This tree wrap is flexible and white to protect trees with smooth bark from injury.

 

Winter-Burn Prevention
Winter burn is a common occurrence to evergreens, including boxwood, holly, rhododendron, and most conifer species. Winter burn symptoms often develop when temperatures warm-up in late winter and early spring, and is often misdiagnosed as an infectious disease or damage from excessively cold temperatures. Winter burn is caused from desiccation, which is a type of dehydration injury. Dehydration and winter burn results when roots are unable to obtain water lost through transpiration. Water loss through transpiration is normally low during winter months, but it increases when plants are subjected to drying winds or are growing in warm sunny spots. Several techniques to minimize or prevent winter burn can be implemented, with varying degrees of success:

  • Carefully choose planting materials, avoiding trees and shrubs that are known to suffer from winter burn (including Alberta spruce, English holly and Colorado blue spruce),
  • Avoid planting broadleaved evergreens like rhododendron in areas of high wind exposure,
  • Deep water plants before ground freeze, and continue to water during winter months when temperatures remain above freezing but without precipitation,
  • Erect physical windbreaks.
  • Wrap problem plants with burlap or other material to protect from wind and subsequent moisture loss to evergreen shrubs and small trees.
  • Various types of antitranspirants such as Wilt-Pruf are available, but have shown limited success. These are very short-lived and must be reapplied every 2 to 3 weeks to remain effective.
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A burlap screen can prevent wind damage.

Container Plants and Trees

Folks who live in small quarters (or just choose to grow plants and trees in containers) come to a crossroad when the nighttime temperatures fall below 15ºF. The problem is this: when the temperature dips to 20ºF and stays there for a while, it’s possible to freeze the core roots of the plants. Until you decide to bring the plants inside, you should thoroughly water the pots prior to cold snaps. This will help protect the roots. It’s easier for freeze damage to occur in a dry container than in a wet container.

When the weather gets cold, and you are working toward winterizing, you can move your container plants into an unheated garage or shed. Prior to moving, thoroughly water the pots. If a plant is cold-hardy, you can leave it outside by mounding 4-6 inches of mulch around and over the top of the pot – heavy enough to provide a protective barrier around the pot. Prior to mounding, you should adequately water the pot. For added protection, consider using some type of rodent bait in the sawdust or mulch to avoid mice depredation.

Keep in mind, some container plants need to be transferred inside because they may not be cold hardy for the zones in which they are planted. If you have purchased a fruit tree but live in a zone-challenged area, know that these plants adapt and fruit well in a containerized situation – as long as they are moved inside for the winter months.

How well we balance our sleep life with our work life can help determine the quality of our senior years. Since a plant endures four seasons each year, its rest period and our care can determine both its performance and longevity.

Checklist on Winterizing Trees & Shrubs

1. Remove visibly damaged and dead wood. Try to make small pruning cuts that minimizes the exposure of the central heartwood on the branch.

2. Prune branches that will touch the ground when loaded with rain and snow. Foliage and branches that are in contact with soil can invite undesirable pests and problems. 

3. Remove damaged and declining twigs, branches, and bark. Do not leave food and shelter for pests during the winter. 

4. Remove any sprouts or suckers growing at the tree base or along stems and branches. Pruning should conserve as many living branches as possible with only a few selective cuts.

5. Spread a thin layer of organic mulch to blanket the soil. Cover an area at least as large as the branch spread. Mulch is nature's way of recycling valuable materials, but be careful of pests hitching a ride.

6. Properly wrap new trees that have not developed a corky bark and could be easily damaged. Injury from the environment, including chewing and rubbing by animals, must be prevented.

7. Aerate soil if it is compacted and poorly drained. It is critical not to damage tree roots in the soil. Saturated and dense soil can suffocate roots.

8. Watering may be needed where soils are cool but not frozen, and there has been little precipitation. Winter droughts need treatment with water the same as summer droughts, except it is much easier to over-water in winter.

 

Sources: 1 ; 2 ; 3 ; 4

August 29, 2018
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