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Cold weather can damage plants

Posted: February 19, 2012 - 1:15am

The weather had been beautiful for most of the past month, with temperatures in the 60s and 70s. Flowers are blooming, trees are budding and plants are starting to put on new growth.

I was expecting more cold weather, and we got it. Every two to three years, a freeze will come in and damage plants. Four or five years ago, there was the big freeze during Masters that did a lot of damage.

This past week, the temperatures dropped suddenly, and I am expecting more damaged plants.

Cold damage can occur on all parts of the plant, including leaves, fruit, stems, trunk and roots. The damage occurs when ice forms in the cells, which expand, burst, then die.

Another way that cold affects plants is through the loss of water, which occurs when there are cold and windy conditions. If there is inadequate soil moisture, the plant will lose water. The leaves will turn brown on the margins and the plant can defoliate.

Another sign of cold damage is bark splitting. The bark will loosen on the trunk of the tree and fall off. On shrubs, the bark will peel off the stem. This usually occurs 3 to 4 inches above ground level. This damage usually is not seen until the plant starts to die in late April and May. The daytime temperatures will be in the 80s and 90s, and the plant will require more water. The water can’t reach the top of the plant because of the loss of bark.

How plants are grown will have a large impact on how well they withstand cold weather. The first step is to buy plants that are adapted to this area and are cold-hardy.

When checking to see if plants will do well here, don’t forget about choosing those that also will withstand the heat and humidity.

Also, every yard has an area that is its own microclimate. These can be low spots that will be colder than high areas. Cold air will settle in a low spot.

Determine which exposure the plants will have. Less cold-hardy plants can be planted on the south side of your house and the more cold-hardy plants on the north side. The south side of a house gets more sun in the winter months.

Proper pruning will help plants better withstand cold weather. The best time to prune most plants is late winter and early spring, and be finished pruning by midsummer. The time to prune will be determined by when the plant flowers or doesn’t flower.

Late summer and early fall pruning will cause new growth on the plant. This growth will not have time to harden off before cold weather arrives and can cause increased winter damage.

All of the previous practices should be done during the planning stage and summer growing stage. But what can be done when a freeze is expected?

Plants can be covered with sheets, blankets or cardboard boxes, which traps the heat radiating from the earth and keeps the temperature higher around the plant. These covers should be removed during the day to release the heat that is trapped by solar radiation.

Plastic is not a good material to use as a cover, because heat builds up more rapidly under plastic and can burn the plants. Also, make sure that no part of the plant is touching the cover or that part will be damaged. Protect plants growing in containers by moving them indoors. If there are a number of containers, they can be pushed together to help trap heat. Also, mulch can be placed around the containers to help conserve heat, or they can be placed under taller plants.

The last thing that needs to be done to protect plants against cold is to keep the soil around them moist. Moist soil absorbs more heat than dry soils.

Plants have water needs during winter. If there is not sufficient rain, the plants need to be watered every 10 to 14 days. To help conserve moisture, put mulch around the plants. The mulch will help keep constant soil moisture and will help protect the root systems of tender plants. Three to 4 inches of mulch will protect the plants.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@comcast.net, or at (706) 836-2152.

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