Winter can be harsh on broadleaf and needle evergreens, especially those that were recently planted. Boxwoods and rhododendrons, spruces and pines are all examples of plants that transpire during the winter – a process where soil moisture is taken in through their roots and expelled into the atmosphere through openings on the leaves and needles. Desiccation injury occurs when water leaves the plant foliage faster than the roots can replenish it. Dry winter winds and sunny days play a part in causing this decline as they hasten transpiration. You can take some precautionary steps this fall to help protect your plants from winter damage.
Start now by watering your evergreens during dry spells. You will need to continue this until the ground freezes. Supply one inch per week when rain or snow are scarce. Once the ground freezes, the plant will no longer be able to absorb water from it. Keep in mind that just because air temperatures go below freezing, it doesn’t mean the ground is frozen – that can happen as late as January in some winters. When temperatures are expected to hit the freezing mark, always remove the hose at the faucet. Water in pipes and faucets could expand and burst causing damage in your home.
Place composted hardwood mulch over the root zone of your plants to a depth of 3-inches to help preserve soil moisture. Mulch at that depth helps to limit wide fluctuations in the soil temperature. Soil that is not mulched will heat up rapidly as the sun shines on it. Then cold nighttime temperatures will bring those temperatures back down quickly. Mulch and snow cover act as insulators and keep soil temperatures more even and warmer overall. Mulch will not stop the ground from freezing eventually.
Evergreens can also be protected from strong winds by loosely wrapping them with burlap. It allows airflow, but limits the amount of it. Another option is to create a two or three-sided burlap screen to protect plants from the wind and sun. Place stakes in the ground before the ground freezes at least a foot away from the plants and attach burlap to them. This should be on the south or southwest side of your evergreen.
Anti-transpirant sprays are designed to help evergreens from drying out. These products are said to work especially well on broadleaves like boxwood. Read and follow label directions carefully for best results.
Julie Moore is a Master Gardener volunteer with the University of Illinois Extension in DuPage County.