As families recover from consuming heaping dishes of traditional delights during Thanksgiving weekend, they can crank up the holiday tunes, dive into boxes of decorations in reds, greens and golds, and begin thinking about another seasonal holiday that will be here before they know it. That's right, I'm talking about Christmas.
Within the coming weeks, you'll notice evergreen trees more clearly, scattered among their deciduous friends in your landscape. Their colors, blends of blues and greens, will dominate your visual attention over the bare, brown branches and blankets of white snow.
You'll also see evergreens appear in your neighbors' large front windows, dazzling those who walk by as sparkling crystal ornaments reflect tiny bulbs in bright, bold colors.
In my town, the holiday cheer has already begun. Inspired to begin our annual decorating frenzy, I recently traveled to the local Christmas tree farm to find the perfect evergreen for my home. As I scanned the overwhelming aisles of trees of all sizes, shapes and species, I was happy to see a large selection of beautiful, "true" blue spruces, my favorite Christmas trees.
This reminded me of the evergreens growing in my backyard. Lately, however, my blue spruces have been looking all but blue. But why?
Perhaps your Colorado blue spruces (Picea pungens), known and cultivated for their beautiful bluish cast aren't showing off their true colors.
Want to maximize the color in your exterior evergreens? According to Greg Mazur, The Davey Tree Expert Company's Tech Advisor, genetics determine the spruce's blue hue, and humans, unfortunately, can only minimally influence the color's vibrancy. However, a better understanding of evergreens and their needles may help to prevent needle discoloration and needle drop, as well as preserve true color.
R.J. Laverne, a board certified master arborist and Davey's manager of education and training, says all conifers lose some of their needles for the same reason deciduous trees lose their leaves in the fall.
Conifers retain needles from the past two to seven years, but each fall the oldest needles typically turn yellow and drop to the ground. Although this is normal, needles sometimes experience discoloration for other unnatural or abnormal reasons.
Although a wide variety of insects and diseases (bacterial and fungal) attack evergreen foliage, the most common reason for needle discoloration is the lack of adequate nutrients in the soil. Trees and other plants need sufficient amounts of nitrogen, potassium, phosphorus and other nutrients to thrive and survive.
Moisture is important for tree survival as well. Drought, or a lack of adequate moisture in the soil, causes needles to yellow, then turn into a rusty red color and finally fall from the branch.
It is especially important to rehydrate plant tissue following a summer or fall drought and before soils freeze because conifers continue to photosynthesize through the winter.
Rhizosphaera needlecast and Cytospora canker, caused by fungi, are common diseases that also lead to needle discoloration. Spores divide on individual needles, but water droplets spread the spores throughout the tree's branches. Moving vehicles may splash road salt onto needles, which results in discoloration as well.
Some insects and mites will also discolor conifer needles while feeding. Eriophyid mites will continue to feed throughout the winter on the sunny, warmer side of conifers, causing injury that mimics wind burn or salt spray.
To help maximize the health of your spruce trees and evergreens, be consistent and follow a proper tree care plan:
- Provide trees with plenty of water during periods of drought, but don't over water during periods of normal precipitation.
- Follow proper irrigation techniques. Temporary mild irrigation may provide the soil with sufficient moisture to make the discolored needles green up.
- Retain sufficient nutrient levels in the soil surrounding your trees. You may need to send a soil sample to your local county extension agency to determine specific nutrient deficiencies.
- Remove lower branches that may be infected with disease. It is always a good idea to consult a qualified, professional arborist to identify which branches should be removed and to make the proper pruning cuts.
Proper tree care is important to help preserve the color of your spruce trees as well:
- Position trees in full-sun exposure to maximize photosynthesis activity. Evergreens typically rely on reserve needles from previous years for sufficient photosynthesis.
- Soak trees at their root lines to avoid water contact with the needles. Water droplets spread the damaging Cytospora canker spores to other branches.
- Practice proper and consistent fertilization techniques each year.
- Protect your trees from heavy snow or ice buildup, as well as soil and airborne road salts.
"Trees are either assets or liabilities," Laverne says. "If you pick the right tree for the right place and do minor maintenance, the tree will provide significant benefits - economic, ecological and social - for many years."
With proper care and maintenance, your spruce trees will be able to show their true blue colors the whole year through.