Be Inspired Seasonally with Rita Calvert
After the winter of 2013-2014, many of us want to be more vigilant to protect our precious trees and perennials from the big chill. For me, my 6 different fig trees are the most important, although like many other gardens, the normally glorious old hydrangea also showed big stress. Crape Myrtle was another tree which the University of MD Ag Extension reported folks were concerned about.
Bundling up for the winter is mostly a matter of cleaning up and covering up as those plants, which aren't killed outright by frost, prepare for dormancy. While it looks like your plants have gone to sleep, there is still a lot going on under the soil and this is the area needing protection. It's important to spread new mulch now -- a thicker winter layer -- to protect plants and soil over the winter months. The idea is more about keeping the temperature even than keeping the plant warm. To begin, cut off diseased foliage from evergreen plants and shrubs and discard it in the trash. Rake up and discard the old, disease-bearing mulch, too.
The following is some excellent information on various types of frost and methods of frost protection from Today's Homeowner. The temperature differentiation between light and hard frost is most helpful, as is understanding how the frost moves within the plants.
What Is a Freeze?
A freeze occurs when temperatures drop below the freezing point of water (32° F or 0° C). When the water inside a plant freezes, it can cause the plant cells to burst, resulting in irreparable damage.
What Is Frost?
Frost occurs on clear, still nights. As the air temperature approaches freezing, the surface temperature of plants can dip below freezing, causing ice crystals to form in the same manner that dew forms on warmer nights. Because temperatures vary just a few feet above the ground, frost can form when your thermometer reads above freezing. Freezing temperatures may or may not be accompanied by frost.
Types of frost include: Hoarfrost is the familiar feathery white frost you see on chilly mornings. It results when water in the air is deposited directly in the form of ice crystals. Rime happens when water is deposited in liquid form through dew or fog which then freezes. Rime has a glazed appearance. Black frost is a term used when frost didn’t form, but plants were nonetheless damaged (and blackened) by freezing temperatures.
Effects of Freezing Temperatures on Plants
For all but the most tender plants, it doesn’t matter whether the conditions produced a frost or a freeze. What’s important is how cold it got and for how long. When temperatures near freezing, a few degrees can make a big difference. To advise gardeners, so they can take proper precautions, different terms are used to describe the severity of a freeze. The chart below explains the various terms that are used:
|Temperature||Type||Effect on Plants|
|Down to 28° F for a couple of hours||Light Frost,
|Usually only harms very tender plants. Ice forms only on the outside of the plant.|
|25-28° F for several hours||Hard Frost,
|Damages foliage and blossoms. Ice forms inside the plant, causing plant cells to burst. Will kill back root-hardy perennials and damage crops.|
|Below 25° F for several hours||Severe freeze||Causes damage to many plants, mostly through desiccation (drying).|
Cover Shrubs and Trees
Larger plants can be covered with fabric, old bed sheets, burlap, or commercial frost cloths (avoid using plastic). For best results, drape the cover over a frame to keep it from touching the foliage and making sure not to crush branches. Fabric covers help to trap heat from the soil, so make sure your cover drapes to the ground. Uncover them in the morning when the temperature rises above freezing. Sometimes it's easier to enclose the shrub in a cylinder and fill it with mulch.
Mulch in the form of hardwood bark chips, fallen leaves or straw are the most common for protecting plants and trees over winter. Our own educator, Gene Sumi tells us that mulch of this kind has air pockets for the plants to breath, while also allowing water through.
Water plants thoroughly before a freeze to prevent desiccation and to add insulating water to the soil and plant cells.
- National Climatic Data Center Freeze and Frost Maps
- Old Farmer’s Almanac U.S. City Frost Char
Using a Harvest Guard™ Plant Protection Bag or just basic cover fabric provides fall, winter and early spring protection from frost, snow, ice and harsh winds. Each bag is the ideal size for shrubs, small trees or potted plants. Made from 1.6 oz reemay to provide protection for any hardiness zone, each Harvest Guard™ Plant Protection Bag also has an adjustable closure that will give a custom fit and added wind security.
For more information contact: University of Maryland Extension Home and Garden Information Center-hgic.umd.edu. (Your tax dollars at work!)