Gwinnett County Master Gardeners Association

Hardiness Zone
The purpose of the USDA Hardiness Zones map is for growers and gardeners to determine which plants will tolerate the area’s climatic conditions. The map’s basis is the minimum extreme temperature that can potentially occur, which is divided into 14 separate zones across the country. Gwinnett County is in Zone 7b, meaning that the winter temperatures could drop to five to 10 degrees, although the occurrence is quite rare. Zone 7b is too far north for some plants, such as citrus plants, which prefer the hardiness zones in Central and Southern Florida. Georgia’s coastal counties are in zone 8b, meaning the temperature could drop to as low as 15 to 20 degrees. Plants that thrive on the coast and the rest of South Georgia, such as oleanders and sago palms, could suffer in our zone during an extreme cold weather event. Most plants for sale at local garden centers have USDA Hardiness Zones on their labels. Make sure your purchase ones that are adapted to Zone 7b.

First and Last Frost Dates
In addition to knowing your hardiness zone, every gardener should know the average frost dates. These dates are the key to successful planting. Just look at the instructions on a seed packet or plant tag. “Plant in spring after danger of frost has passed.” Or, “Plant six weeks before the first frost in fall”. Frost dates are also important when it comes to pruning and executing pest control measures.
Average frost dates are based on historical weather data and may or may not hold true every year. In the spring, planting instructions often refer to the average date of the last frost, which is the date on which the last frost has already occurred. Remember – this is an average. This means that if you plant after this date, there is a good chance there will not be any more frosts and frost-sensitive plants should be safe outdoors. Still, you should watch the weather forecasts and be prepared to provide protection … just in case.
The first frost date of autumn helps you time fall plantings, when to bring your tender houseplants indoors and when to harvest tender vegetables. Again, the first frost date is an average and frost may occur before then. It is best to keep an eye on the weather and be prepared.

Authors:
Timothy Daly, University of Georgia Extension Gwinnett County | Agriculture and Natural Resources County Extension Agent
Ann Langley, Master Gardener Extension Volunteer, Class of 2017

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