Jonathan Heaton is an International Society of Arboriculture-certified arborist working for Bartlett Tree Experts in St. Paul, Minn. He can be reached at or on twitter @mnarborist.

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Tips for Winter Tree & Shrub Care
by Jonathan Heaton       #Trees   #Winter

Narrow angles at branch unions will develop into weak branches when mature.

Winter can be a difficult time for our trees and shrubs. Cold weather, snow, wind and more threaten their health. I’ve seen too many trees and shrubs lost that could have been saved with the right care. By caring for the roots, stem and crown you can maintain healthy and attractive plants through the most trying season of the year.

A healthy root system and good soil to live in is the critical foundation for plant health. Preventative care during the growing season will help to protect the root system during winter. (If you missed it last year, put it on your to-do list for the coming season.)

Good soil has pore space, which means it is not compacted and has pockets of air, organic matter and plenty of nutrients. I always order a full soil analysis to test for macro and micro nutrients, pH, organic matter, and, if I suspect it’s a problem, salt levels.

Protect the root zone with a 2 to 4 inch layer of mulch. Keep mulch a few inches away from the stems or branches of shrubs and the trunks of trees. Mulch improves moisture retention during the growing season and helps keep the roots from freezing in the winter. Mulch also adds organic matter over time. Adding a thin layer of compost over your yard each year will improve the soil significantly.

Avoid any kind of plastic or fabric over the root zone. Water regularly when there is no rain, as late into the season as possible. Trees prefer a slow, deep soaking equivalent to at least 1 inch of rain a week — or 5 gallons per square yard. Automatic sprinklers usually don’t provide enough water.

If nutrients are low, you can apply the appropriate fertilizer to the soil surface, but it’s best to mix it in water and inject the solution beneath the surface. You’ll need a professional service for this. If the pH is too high or alkaline, apply sulfur, or if too low or acidic, apply lime, in small amounts several times during the year. Trees have good natural defenses, but they need the right growing environment to take up the nutrients they need to stay healthy.

Winter chemical threats
This time of year a big threat to the roots is salt from deicing products. High levels of sodium will dry out plants even when water is plentiful. Don’t use more salt than you need to melt the ice, and mix salt with abrasives, such as sand. Where possible, drain salted areas away from plants. You can also purchase deicers, such as calcium chloride, which are not sodium based. Plant salt-tolerant species near roadways or put up barriers to protect from salt spray. If an area has been exposed to a lot of salt, apply gypsum and irrigate in the spring.

Animals, such as voles and rabbits, like to chew on stems of many plants. Protect stems by wrapping them with soft fabric or paper. This also helps to prevent frost cracking on thin-barked species, such as maple. Be sure to remove any wrap on the trunk in the spring.

You can also put up a wire fence around plants that need protection. Bury the fence a few inches underground and make sure it will be 1 to 2 feet higher than the snow. Repellants with thiram can be sprayed on the trunk, branches and foliage in cases where other protection is not practical or desirable.

Protect your plants from snow removal equipment by marking the edges of areas being plowed with stakes. Designate where snow should be pushed away from plants. Avoid aiming your snow blower directly at the trunks of trees, as snow and ice can be very abrasive.

Winter is a great time to care for the crown with pruning. Focus on developing a strong central leader, good branch spacing and removing branches with weak or narrow attachments. Dense branches can be thinned to reduce the amount of wind, snow and ice they will catch. Dead branches can also be removed. If you find them hard to spot when the leaves are gone focus on the buds—dead branches won’t have any.

In cases where pruning cannot correct weak limbs, structural support can be installed. In large trees, high-strength steel cable is attached to bolts that go completely through the limb. Cabling should be left to professionals.

Crimp and washer (newly installed) are used for a wire support system between weak branches.

Side view of wire support system.
Side view of wire support system.

Evergreens can catch large amounts of snow, causing limbs to break. Gently brush off the snow. Some evergreens, such as arborvitae (Thuja spp.) splay easily. These can be wrapped tightly with twine or burlap to keep the branches intact.

Evergreens can also be sensitive to winter burn. This is caused when it is warm enough for the needles to lose moisture, but the soil is too cold for the plant to absorb water. The dried out needles turn brown. Minimize moisture loss by wrapping with burlap or protecting the windward side of the plant with a barrier.

Despite the challenges of winter, diligent care can help to ensure you will enjoy them year round.

A version of this article appeared in a January/February 2013 print edition of State-by-State Gardening.
Photography courtesy of Jonathan Heaton.


Posted: 01/01/14   RSS | Print


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