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Take steps to prevent cold-weather damage to plants

Even though we have had some warm weather lately this winter, the cold will surely return. Some precautions should be taken to protect plants from the cold.

Freezing temperatures can cause cold injury to fruit, stems, leaves, trunk and roots. Water inside these plant parts freezes and expands, tearing cell walls causing them to leak. This damage, however, may go unnoticed until the plant fails to come out of dormancy in the spring.

There are three types of cold injury. The first is called burn. Cold-damaged plant parts will often become mushy and turn brown or black. Over time, the damaged leaves or stems will dry out and appear to have been burned with a torch. Sunken areas may appear on branches and trunks with peeling of the bark.

The second type of cold damage is desiccation. It is caused by winter winds. Cold air does not hold moisture like warm air and plants can dry out if the winds are sustained for long periods of time. Leaves may dry up at the edges and eventually turn completely brown.

The third type of winter damage is wood splitting, also known as "frost cracks." This damage occurs on stems and branches. On particularly cold nights, water in the cells just beneath the bark of trees and shrubs freezes. The following day, the warmth of the sun hitting these areas causes the water to thaw out quickly - killing the plant's cells and splitting the wood. Eventually, lengthwise cracks may appear, though they are often not evident until the following summer.

To prevent cold damage to plants, start by selecting plants that are either native to our area or acclimated to the temperatures here. To review the country's climatic zones, which are based on the coldest temperatures in different regions, visit the USDA Web site's at www.usna.usda.gov/Hardzone/ushzmap.html. Plants are categorized according to the areas in which they are hardy to make it easier for gardeners to choose the right plants.

Other ways to protect tender plants during the winter include:

- Plant site selection can be crucial to winter hardiness of some plants. Planting under a tree canopy or near the southwest side of a home to maximize evening winter sun can protect plants.

- Plant nutrition can play a minor role in freezing. Maintaining proper fertility levels can lower the temperatures a plant can tolerate by 5 degrees.

- Windbreaks can be constructed or planted to block frigid winter winds.

- Plants can be covered with fabric on cold nights. Be sure to remove the fabric every day.

- Watering plants keeps them hydrated and prevents plants from drying out due to cold air and frozen soil.

Timothy Daly is an agricultural and natural resource extension agent with Gwinnett County Cooperative Extension. He can be reached at 678-377-4010 or timothy.daly@gwinnettcounty.com.