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Winter burn

IDENTIFICATION — The leaves of your broadleaf evergreens look green now, but the leaf edges of broadleaf evergreens, such as boxwoods (Buxus spp.), turn bronze in winter.

DAMAGE — Plants can experience winter burn, even in milder climates, as they contend with cold, dry air and wind. That wind can suck the moisture right out of leaves. And if water isn’t plentiful or the ground is frozen, the roots can’t take up any additional moisture. In a worst-case scenario, the branch can dry out completely and die.

CONTROL — Prevent winter burn by watering your plant well during dry spells through­out the growing season, as well as during warm spells in winter. Mulch to keep soil moist in summer and prevent rapid soil temperature changes. Also, apply an antidesiccant spray, such as Wilt-Pruf^®, in late fall and again in late winter. Products like this help reduce water evaporation from leaves.

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Cytospora canker

IDENTIFICATION — If your Colorado spruce (Picea pungens) has dead branches, Cytospora canker could be to blame. Yellowing needles is the first noticeable symptom. The discolored needles show up in spring or early summer, change to purple, then turn brown and fall off in winter. The process is repeated each season until an entire branch is dead. A closer look shows a clear, sticky resin oozing from the affected branch. Over time, the resin accumulates to form a ridge surrounding the canker, or dead tissue, and dries blue-white. Any branch on the tree can become infected, but the lower ones tend to be first. Cytospora canker won’t usually kill the tree, but it does disfigure it.

DAMAGE — This disease is caused by a fungus called Cytospora kunzei (or Leucostoma kunzei), which enters through wounds. The fungus is spread by wind, rain, insects, birds and mammals. Cankers generally start at the base of a branch and grow around it until the branch is girdled and dies. It can take several years or even decades to girdle a large limb or the trunk.

Colorado spruce living east of the Rocky Mountains are most often affected. Spruces 10 to 15 years old and those stressed by environmental factors, such as drought, are most susceptible. Norway spruce, Douglas fir and other evergreens can also become infected, although less often.

CONTROL — There’s no cure for Cytospora canker, but there are some preventative
measures you can take. First of all, avoid environmental stresses by planting your spruce in moist, well-drained soil and giving it plenty of space to grow. Deep watering during dry periods and annual fertilizing will keep your tree healthy. Also, avoid injuries to the bark so the fungus won’t have an entry point.

If you notice infection, remove the affected branch close to the trunk during dry weather so rain doesn’t carry spores into the wound. Clean your pruning shears or saw in a 10-percent bleach solution between cuts.

There’s a conifer for almost any landscaping situation. They can be mixed into perennial gardens or foundation plantings. Some make wonderful hedges, shrub borders and even specimen plants. But sometimes you need to prune conifers to keep them looking their best and in scale with their surroundings.

Timing is important when pruning conifers. Spring is a good time to prune many of them. But within that, some recover best if you prune before new growth starts, and others do best if you prune just as the new growth is starting: With many junipers, false cypresses, yews and hemlocks, prune in early spring, before new growth stretches. That way the new foliage will cover up where you’ve cut so you’re not left all season with a plant that looks as if it just had a haircut. Pine, spruce and fir are best pruned just as new tips, the candles, begin to stretch in spring. All you need to do is nip back the shoots before the new needles form.

PHOTOS: © Richard Bloom

The ‘Prostrata’?spruce (Picea pungens) in the top photo is beginning to get too large for its place in the garden. Rather than remove it, prune it. The first step is to cut back the branches that are forming leaders. Click on the photos for larger images.

Next, shorten the longest side branches. Never cut the stem back to a point where there’s no foliage left. If you do, some, such as yew and hemlock, will leaf out again. But most won’t, and you’ll be left with lots of bare stubs. The spruce in the second photo still has a natural-looking form, but now it fits better in its surroundings and new growth will quickly cover the cuts.

For more information on pruning all kinds of plants, check out The Pruner’s Bible at right.

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Winter burn

Winter burn causes an evergreen’s foliage to die off. The most common cause is desiccation. See how the exposed half of the juniper at right is brown while the side protected by the fence is just fine? This is a classic example of winter burn. If the shrub is in a windy or exposed area, such as the southwest side of a building, sun and wind draw the moisture out of the foliage. Because the soil is still frozen, the plant’s roots can’t take in replacement moisture, and the dried-out cells die. Once it’s brown, evergreen foliage won’t come back. So in spring, when the branches start to warm up and become supple, prune brown areas back to the first green shoots. New growth will eventually fill in the bare areas, but you may want to replace unsightly evergreens that have been badly burned.

To keep moisture in the plant, apply an antidesiccant spray, such as Wilt-Pruf®. These sprays contain natural, waxy resins that seal leaves and needles and prevent water loss without damaging the foliage. Apply antidesiccants to an evergreen’s most vulnerable sides after the ground freezes. For especially tender plants, such as arborvitae, hemlock and yew, spray all the foliage. Broadleaf evergreens, such as rhododendron and holly, should also have all of their leaves coated, top and bottom. Spray when the temperature won’t drop below freezing for 24 hours. One coating lasts about two months in winter sun and cold, then needs to be reapplied for maximum protection.