Q: I have seen many trees and plants that were winter killed. Is there any way to protect plants and trees from winter kill?
A: “Winter kill is a prevalent problem in the landscape,” said Micheal Metcalf, landscape architect for Kimberly Nurseries. “There are a few steps that one can take in order to minimize the problem.”
1. Make sure that the right plant is planted in the right location. Select plants for the right climate, exposure, temperature variations, micro climate, and hydro zone.
2. Plants that are more likely to suffer from the cold temperatures can be given some protection by installing a thick layer of mulch around the base of the plant and covering the root zone before winter hits.
3. Give the plant plenty of water before the first hard freeze. Plants still use water throughout the winter. We tend to winterize sprinkler systems too early, cutting off much of the needed water to the plant material. A good slow soak over the root zones of the plant materials will help the plants make it through the winter.
4. Some evergreen shrubs, such as arborvitaes and euonymus — those that keep their leaves much longer — can suffer from water loss due to winter winds and direct winter sunlight. If you have these kinds of plants that suffer, spraying an anti-transpirant (wilt-proof) substance on the plants prior to winter can help them survive.
“The first hard freeze can happen any time, usually sometime in October or November,” Metcalf said. “But it is unpredictable and varies year to year.”
“In the Magic Valley, sprinkler systems should be winterized starting in October,” he said. “They can handle minor freezes without problems. If there are portions of the sprinkler systems exposed above ground, they can be wrapped in insulation or burlap in order to protect them from an early freeze until the winterization is completed.”
“The latest USDA Plant Hardiness Zone map shows the Twin Falls area as a 6B. I have found this to be generous,” he said. “I tend to treat the area as a 4 to 6 depending upon the micro-climates I am dealing with. For example, out in the open and north facing slopes would tend to be zone 4 hardiness. South facing slopes, more direct sun, or protected areas can support most zone 6 hardiness plants.”
“One should not rely upon the hardiness zone map exclusively,” Metcalf said. “One of the most vicious elements in the Magic Valley to plant material is the winter winds. They tend to be harsh, dry, and cold. Things plants tend not to like very well. One kind of plant may thrive in a protected residential yard in downtown Twin Falls. However, put that same plant on a more open landscape out in the country and it may not last the winter.”
“When planting new plants, soil conditioning is very important. Soil additives or conditioners such as peat moss, compost, and bark mulch all add organic material when mixed into the soil and improve the soils water holding capacity,” said Metcalf. “These also provide some of the nutrients the plants will need in the long run to survive and thrive. We also recommend adding a mycorrhizae additive. Mycorrhizae develop the root system through a more efficient uptake of water and nutrients by the plant. The use of a B1 root starter will also improve the survival rate of the plants.”