When do we expect the last frost?

Taken from the CASE website and written by Pam Knox, University of Georgia Agricultural Climatologist

Now that March is upon us and the atmospheric pattern has shifted into something that is bringing more spring-like weather to the Southeast, it’s time to think about planting.  And that means thinking about the last frost of the winter.

AgroClimate has a tool which shows the last frost date by county for the Southeast.  The 50 percent map shows the average date for the last frost, while the 10 percent map shows the date that one in ten years will see a frost, and the 90 percent map shows the date for which in just one out of ten years the last frost will come early (or in other words, in 9 out of 10 years the last frost will come later than this date).  The maps below show the dates for 32 F.  You can find the tool athttp://agroclimate.org/tools/Freeze-Risk-Probabilities/.


If you need the information for a different temperature threshold, then a good source of information is the Southeast Regional Climate Center.  You can go to their web page www.sercc.com and pick “Historical Climate Summaries” from the “Climate Data” menu at the top.  Pick your station and then look for “Spring Freeze Probabilities” on the left menu.  Here is the graphical output for Tifton, GA.


What this shows is that for Tifton, for a temperature of 32 F (orange line) at the 50th percentile (for the average date), the date is about March 10.  You can click on the link for tabular data to get a table of numbers instead of the graph shown here.  Keep in mind that this is for the period of record for the station, and that last dates for spring freeze have been trending earlier in the season in recent warm years.  If you have a different source of freeze information that you like to use, please let us know!

Landscapes may be more at risk of a late frost this year

Merritt Melancon is a news editor with the UGA College of Agricultural and Environmental Sciences

The northern and southern halves of the state vary slightly, but Georgia’s last frost typically falls between mid March and mid April. On some years the last frost has hit as late as May. University of Georgia Extension climatologist Pam Knox believes the current neutral weather pattern — one not affected by La Nina or El Nino — could put Georgia at greater risk for one of these rogue late frosts.

There’s no way for a gardener to predict or stop a late frost from hitting after they’ve put in transplants or started counting sprouts, but they can be prepared, said Paul Thomas, a UGA Extension horticulturist. Since no one knows when a frosty night might hit, gardeners should have a frost tool kit and game plan ready.

“Buying or collecting frost reduction materials prior to the frost and pre-positioning them close to the plants you want to protect is very important,” Thomas said.

One of the most effective ways to shield plants from frost is to cover them with any of a wide variety of materials, from high quality frost–reduction fabric, to blankets and sheets, to newspapers, baskets and straw.

For small shrubs such as Gardenia, a supply of old comforters or heavy blankets — maybe purchased from a local thrift store — will allow you to protect your plants from that first frost without spending much money. Covering plants with a heavier blanket will protect them more than if they’re covered with a simple sheet, Thomas said.

In addition to blankets, simple mulches — like dead leaves or grain straw — are some of the best materials for protecting small plants and flowers. For smaller plants such as young vegetable starts, lighter weight material like pine straw works great if enough is placed over the plants.

Gardeners can completely bury their newly flowering shrubs or tender garden seedlings in either leaves or straw, and then uncover them after the weather warms back up. The flowers and seedlings will be fine, he said.

Never use plastic sheeting to cover plants because plastic can trap too much heat. When the day starts to warm up, the plants can actually cook or scorch under the covering. “By 10:00 a.m. you can have significant damage to grass and young plants due to how quickly it can heat up under that plastic,” Thomas said.

It’s best to cover plants before sunset to retain some of the heat that is trapped in the soil and remove the coverings in the morning just after sunrise to prevent the plants from being scorched. The exception would be if it’s cloudy, snowing or icy.

Thomas also recommends having a collection of wooden garden stakes on hand. Place the stakes throughout your vegetable patch in order to suspend blankets over tender seedlings or delicate flowers. The stakes will prevent snow or rain soaked blankets from crushing your plants, Thomas said.