Enjoy Taking Risks? Try Predicting Final Frost

— Written By and last updated by Diane Lynch

Q: When is the last chance for frost this spring?

A: We all know the weather can be very hard to predict, especially in North Carolina. Now that we are starting to have warm spring temperatures, many gardeners get spring fever and want to start on their vegetable gardens. One of the challenges gardeners face is when to plant warm-season vegetables and not be affected by a chance of late frost.

Frost forms on solid objects when the water vapor in the atmosphere changes from its vapor (gas) phase to small ice crystals (solid phase). For frost to form on an object, the object has to reach 32°F or lower. However, the air temperature within the vicinity of the object can be several degrees higher. It does not take long to realize it can be very hard to predict when our last spring frost will be, especially as we have warm spring days and cool nights.

There is lots of variation in the date when we have our last frost in Wayne County. The last frost date has been as early as mid-March and some years as late as the beginning of May in our area. Often many resources give gardeners a guideline by finding the average last frost date. Even though it may sound simple enough to take the average of all the last frost dates over the years, there is much variation in what resources claim as the last average frost date. In doing a search of what different resources say is the average last frost date for Goldsboro, it ranged from March 28th to April 20th. The ranges vary depending on how many years of data are include in the average and takes into consideration how often it does not occur on that average date. We often pick somewhere in the middle and say around April 15th is the last average frost date in Wayne County. Remember, however, there is no guarantee that there will not be a frost after April 15th.

So what is a gardener to do when they are ready to plant warm season vegetables, like tomatoes, peppers, beans, and squash, in their garden? It all depends on if you want to be a risk taker or play it safe. Some gardeners go ahead and start planning warm-season vegetables around the first of April knowing that they could lose their plants to a late frost, while others wait until around the first of May when the chances are much less for frost.

If you do plant early, you have to be prepared to cover and protect your plants if we do have a late frost. Row covers made of light-weight fabric that will be sun and air permeable work well for quickly covering plants if a frost is predicted. Many try to cover plants with plastic because it is often what they have on hand for a last minute solution. Plastic covers usually create more plant damage than good. Plant leaves in direct contact with the plastic can be burned and if the plastic is not removed early in the morning, you are creating a mini-greenhouse that will quickly over heat your plants and not allow air to get to them. When covers are used they should be removed the next morning as temperatures increase to prevent further plant damage.

As you plan for planting your vegetable garden keep in mind that we are not necessarily out of the clear for having a late spring frost. We never know if we have already seen our last frost for the season or if we will have some more cold temperatures come our way later this month.

For your gardening, landscape, and lawn questions contact the Wayne County Extension Master Gardener Volunteer Plant Clinic on Mondays and Wednesdays from 10 a.m. to 1 p.m. The plant clinic is a free service open to any citizen in Wayne County that has home gardening questions. One can reach the Wayne County Extension Master Gardener Volunteer Plant Clinic by phone at 919-731-1433, e-mail at Master.Gardener@waynegov.com, or stopping by Room 100 of the Wayne County Extension Office (208 West Chestnut Street, Goldsboro). People contacting the plant clinic with questions are encouraged to bring samples and/or pictures that could help in reaching a solution. Extension Master Gardeners are trained volunteers with the Wayne County N.C. Cooperative Extension Service.

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Jessica Strickland
Extension Agent
North Carolina Cooperative Extension
Wayne County Center
P. O. Box 68
Goldsboro, NC 27533
E-Mail: jessica.strickland@waynegov.com
Phone: 919-731-1525
Fax: 919-731-1511