Protect Your Garden After the Warm Winter
Saturday, March 24, 2012
This winter was one of the mildest on record. Mild temperatures like this encourage growth and flowering. In some cases, you can already see the tips of tulips, daffodils, and other bulbs blossoming. Most bulb species are quite hardy and can withstand cold temperatures. At worst, there could be some blemishing of the foliage but the plants should survive. Nevertheless, it won’t hurt to place wood chips or pine bark mulch over them to protect them.
Woody plants are a different story. Sudden drops in temperature can still injure them even at this late date. They’re especially susceptible when a cold snap occurs after a mild winter. Below are tell tale signs of a cold injury:
• Black-heart in stems of trees and shrubs: Plant shoots and twigs appear limp and flaccid, but still green on the outside. The stem bark shows turns black. Black-heart affects maples, lindens, and ashes, as well as the lilacs and viburnums.
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• Winter burn of conifer foliage: Pine, spruce and fir needles often turn brown and brittle, thanks to sudden changes in temperature. The browning starts at the tips of the foliage and progresses downward toward the base. Eventually, the entire needle discolors.
• Sunscald of tree trunks and branches (aka frost canker): Dead, sunken areas appear on the stem’s surface. This coincides with the injury or death of the cambium layer below the bark. Wide temperature fluctuations predispose the plant to sunscald damage. London plane trees, elms, beeches and oaks are especially susceptible, especially when they’re young and their bark is thin.
Protect Woody Plants
You can’t do much now to protect woody plants from temperature swings or sustained periods of cold in the next few weeks. But you can prevent cold injuries to woody plants in the future. Below are tips on how to do that.
• Select only hardy species:
Buy and plant woody plants capable of surviving the average annual minimum temperatures for Plant Hardiness Zone 6 (-5°F to -10°F).
• Plant in mid to late spring
Timing is critical for successful spring planting. Later spring planting is better than earlier to avoid the possibility of a quick frost that can damage or kill saplings.
• Plant to the equator side (south) of buildings, walls, and windbreaks
These objects absorb, store and, then, re-release radiant energy (heat) from the sun into the surrounding environment. This heat transfer warms the air, keeping plants from freezing.
• Avoid late summer fertilization and irrigation
These cultural practices promote the development of tender shoots and leaves late in the season. They also delay the on-set of cold hardening in plants. Early frosts can cause irreparable harm to plants with little or no protection from the cold.
• Delay pruning until just before growth begins
Plants lose their cold hardiness quickly as temperatures increase with the approach of spring. Conifers as a rule become more sensitive to cold than deciduous plants. Pruning in late winter triggers shoots to emerge from dormant buds. Pruning also exposes cambium and xylem to the elements when the bark that protects them is wounded or stripped away.
Insects are also a concern thanks to the mild winter. We really won't know how the winter affected them for a while. Many will emerge early as the warming temperatures hasten their development, creating a banner year for wood defoliators, such as the Winter and Gypsy moths and the spring cankerworm. All are voracious eaters. But things tend to balance out in nature.
The Rhode Island Tree Council teaches proper plant techniques in its Tree Steward’s classes. For more information, contact RITree at (401) 764-5885, or by e-mailing [email protected] . For some fun facts on trees, go to the Trees Are Good Web site.
John Campanini is technical director of the Rhode Island Tree Council. Previously, he was Providence’s city forester.
