Winter can be unkind to needle evergreens and the broadleaf variety…especially those evergreens that were recently planted in the ground. I discovered this the hard way…after two Dwarf Globe Blue Spruce I planted several years ago in September died over the winter. I now know how to prevent this…read on for cold weather protection tips for your evergreens.
Pines, spruces, firs, yews and junipers are examples of needle evergreens popular in Zone 5. Rhododendrons, hollies, and boxwoods are types of broadleaf evergreens that do well in our area. High winds and winter sun increase moisture loss which stresses the plants, leaving them open to winter drying and wind burn. If the plants were recently installed, they have a small root system compared to what it will be in future years. In the future, you may not need to help the plant get water, but the first few years are critical.
I think many people forget that rhododendrons are in the evergreen family…thinking evergreens all have needles. Rhododendrons are actually perfect four seasons plants. Blooming in the summer with colorful flowers, standing out with shiny summer foliage, displaying a nice range of fall colors, plus a good contrast to deciduous plants and conifers by offering winter interest.
Most evergreens do best in well drained soil and should be planted in full sun to at most partial shade. They all provide winter interest since they retain the majority of their needles or leaves. To prevent moisture loss through the leaves (known as transpiration) you can apply a product such as Wilt-Pruf in the fall (Wilt-Pruf is a natural product derived from the resin of the pine tree). Maintain with a layer of mulch.
Rhododendrons should ideally be planted in a site that provides some protection from drying winter winds. These acid-loving plants curl their leaves downward when temps fall below 28 degrees F. The colder the temperature…the tighter the leaves curl. This reduces the leaf surface able to retain water.
In more exposed area an anti-desiccant can be applied in the fall to deter moisture loss. It helps to mulch yearly with a low pH material such as pine needles, pine mulch, or decomposed oak leaves.
Transpiration is the process where soil moisture is taken in through the roots and expelled into the atmosphere through openings in the leaves and needles. Desiccation injury occurs when water leaves the plant foliage quicker than the roots can replenish it.
Starting in mid-October water your evergreens during dry spells. Continue this until the ground freezes. As a rule of thumb, supply one inch of water per week when rain (or snow) is scarce. Once the ground does freeze, the plant will no longer be able to absorb water from it. Remember that just because the air temps are below freezing doesn’t mean the ground is frozen. In recent years with the warming trends…the ground sometimes doesn’t freeze until January.
Make sure to remove the hose from your outside faucets when temperatures hit freezing. Water in pipes and faucets could expand and burst causing damage to your home.
Place hardwood mulch over the root zone of your plants to a depth of 3 – 4 inches to help preserve soil moisture. Mulching at that depth can limit wide soil temperature fluctuations.
When soil is not mulched, it can heat up rapidly when the sun shines on it. When the sun goes down, cold nighttime temperatures bring those temps back down quickly. Snow and mulch act as insulators for your evergreens…keeping soil temperature more even and warmer overall. Don’t worry mulch will not prevent the ground from freezing eventually.
Burlap can be used to protect your evergreens from strong drying winds. Loosely wrapping your plants allows airflow, but limits the amount. You can wrap them as a cylinder or use garden stakes to create a 3 or 4 sided burlap screen. Place the stakes in the ground before it’s frozen. Keep them 6 – 12 inches away from your evergreen on the south or southwest side preferably.
You don’t want to suffocate the plant, just block some wind. Burlap is ideal since it breathes. Plastic would cause a greenhouse effect since it would block the wind, but not allow air through.
Anti-transpirant sprays are designed to help evergreens from drying out by sealing the moisture in. These products work especially well on the broadleaf type evergreens, but can aid all types. Make sure to read and follow the instructions carefully before applying for the best results.
Two products of this type include Wilt-Pruf and Cloud Cover. These films are often sprayed on harvested Christmas trees to help reduce the water loss from the needles. Both are available online or at garden centers. Don’t spray when anti-transpirant can freeze on plant leaves. Note: Blue Spruce may appear green or faded for a short period of time after application, but this effect disappears quickly.