Cold can pose problems for plants

This has been a year of extremes. Early in the year, we were in a severe drought. In late summer, we started getting some rain, and as the season changed to fall, the rains continued.

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In fact, for the first time in a number of years, the lake was full.

Not only did we get an abundance of rain, the temperatures remained warm. Most people I have talked with have enjoyed this warmer weather, but it could cause our plants some problems.

The forecast, as I write this article, is for temperatures to drop into the mid to low 20s in coming days. This degree of cold could cause some problems for plants because they have not hardened off.

Under normal fall temperatures, the plants would slow or stop growth for the winter. I saw some plants this past week that were putting on new growth.

The questions most gardeners will have are: What damage can this sudden drop in temperature have on my plants, and what can I do to help them?

Cold damage can occur on all parts of the plant, including leaves, fruit, stems, trunk and roots. Most people notice the damage done to the leaves, fruit or stems. These parts of the plant can turn black, brown and become mushy.

The damage occurs on the plant when ice forms in the cells, which expand and burst.

Another way that cold affects plants is through desiccation -- the loss of water in a plant. This occurs when we have cold conditions and wind. If there is inadequate soil moisture, the plant will lose water. The leaves will turn brown on the margins and the plant can defoliate. This year this should not be a problem because of the high levels of soil moisture.

Another sign of cold damage is bark splitting. This symptom doesn't show up until later in the year. 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. We might not notice the split bark until May or June of next year.

What should be done with plants if they are damaged by the cold?

The first thing to do is to wait. This can be hard for many gardeners who feel they need to do something to help the plant. The best thing to do is give the plant time to recover. By waiting, it will give the plant time to put on new buds and growth. Then it will be OK to prune out parts of the plant that don't grow.

Also, make sure the plant doesn't go through any drought stress. Don't do anything for the plant until it is time for the normal pruning.

There are a number of practices that can help plants survive sudden drops in temperature.

The first is to select a plant that can tolerate cold temperatures. When buying plants, check the tag or look up the plant in a plant book to determine the minimum temperature the plant can withstand. In addition, think about the heat index of the plant as well. Will the plant survive our summers? Our area will fall into the plant zone 7a or 8b.

In addition to plant selection, think about the micro-climate of the yard. Every yard has areas that are hotter and colder than other areas.

During the winter, the north and northeast portions of a yard will be the coldest. The southern areas will be the warmest.

Why is this important? When planning where to plant, the least cold-hardy plants should be placed on the south side of the yard. These plants will do better near the house or buildings, because the buildings hold heat and this keeps the temperature around these plants higher. Plants that are cold-hardy can be planted in other areas of the yard.

Plants that have the proper nutrition and moisture levels have a better chance of surviving freezing temperatures. Fertilizing plants at the proper time of the year will give the new growth time to harden off before cold weather arrives. Plants that are fertilized too late will put on new growth, and this growth is more prone to cold damage. All fertilization should done by the end of August.

Also, plants need to have adequate water to help survive cold temperatures. Therefore, check the moisture level around plants before a cold snap and water if necessary. Moist soil absorbs more heat, which helps to maintain an elevated temperature around the plants.

A mulch layer 3 to 4 inches deep around plants will help conserve moisture and maintain higher soil temperatures and protect the root system of plants.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@comcast.net.