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Despite warmer weather, the risk of late frost not over yet

In recent weeks, our area has experienced some warm spring days, and often this weather puts people in the mood to begin planting for the summer. But be forewarned: the danger of a killing frost has not passed. The average last date of frost in our area is usually between April 15 and 20, although it varies year to year.

Most spring flowering shrubs and trees, such as fruit trees, set their buds in the late summer and fall of the previous year. They require a certain number of chilling (temperatures below a certain minimum, like 40 degrees) hours to initiate their blooms. We had plenty of cold weather in the winter months of 2007, and upon the arrival of warmer weather months in March, the spring flowering plants began to bloom.

Unopened buds are resistant to cold temperatures: However, newly opened flowers and young, tender growth is most susceptible to freezing temperatures.

Peaches, apple trees and blueberries, major commercial fruit crops here in Georgia, are among the earlier flowering plants. On Easter Sunday in early April 2007, a late season frost hit with temperatures well into the 20s, even in the southern part of the state. A majority of these crops were lost, and that, along with the drought, has put a heavy strain on the orchards. The freeze also caused harm to our home gardens. Gardeners who had these fruit trees and shrubs in their yards lost their crop as well.

Other spring flowering trees and shrubs had their flowers and new growth frozen back. Outside my church on that Sunday, I observed the new growth on the crape myrtles were frozen and had turned black. However, most of these plants were able to recover and grow through the season. The Extension office advised people to wait a couple of weeks after the freeze and then prune out the stems and branches not producing leaves. Most woody plants with new growth and flowers were affected by the freeze still produced leaves and growth later, and summer flowering plants, like crape myrtles had flowers.

The Extension office received numerous calls from people who had planted tender vegetable plants, such as tomatoes and peppers, as well as herbaceous flowering plants that were not cold hardy and they asked what could be done to save their plants harmed by the freeze. The recommendations we gave were to remove those plants since they were most likely dead, and replant with new plants after the danger of frost has passed.

If such a late season freeze is forecasted, young, tender plants with new growth and open flowers can be covered with a sheet or plastic cover to give some protection, but there is no guarantee this action will save the plants. Remove the following day to keep temperatures from building up under the cover.

The best course of action, when planting spring flowers and vegetables, is to wait until after the danger of frost has passed in the middle of April. However, the soil temperatures are still low, and may delay germination of seeds such as squash, cucumbers, beans and peppers. Consider waiting until May 1 or later to plant these seeds when the soil temperatures are warmer. You can start them indoors in small containers, such as peat pots, and then plant them outdoors, or you can buy transplants at local garden centers.

Although the weather has been warm lately, a late freeze can still occur, and should be taken into consideration when planning your garden. For more information on local weather conditions, including soil temperatures, go to the Georgia Environmental Monitoring Network at www.georgiaweather.net. If you have any questions regarding planting around freeze dates, please contact the Gwinnett County Extension office.

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