Georgia Garden Girl

Garden Great in Zone 8!

What Is a Frost Date?

For planning purposes, you need to know your area’s first and last frost dates.  Why?  Well, when the temperature dips to 32° F and below, that’s bad news for your warm season plants.  These days, when the mercury routinely hits 70° F and above in January, it’s easy to forget about frost.  But we do still have frosts and hard freezes in Middle Georgia, so it’s a good idea to take the first and last average frost dates into account when you plan your warm season flowers and vegetables.

The fine folks at the National Climatic Data Center keep track of the average temperatures around the country.  Based on that data, they calculate the chance of frost for a given date at each tracked location.  It is useful to know your first average fall frost date so that you can understand the best time to plant late summer successions of warm weather crops.  But my focus is usually on the last average spring frost date—the date when I can (safely) get some warm season crops in the ground.

For the NCDC tracking location nearest my town in Middle Georgia, there is a 10% chance that the temperature will go down to 32° F (but be above 28° F) on or before April 9.  Therefore, I refer to April 9 as my 10% frost date.  There is a 50% chance that the temperature will go down to 32° F (but be above 28° F) on or before March 23.  Therefore, I refer to March 23 as my 50% frost date.  Incidentally, on that same date, there is only about a 10% chance that the temperature will go down to 28° F.  This is what some people refer to as a hard freeze, though a hard freeze is also defined as a temperature at or below freezing, 32° F, for enough time to kill seasonal vegetation.

To find your frost dates, visit the frost date calendar from Dave’s Garden.  You can also check out the primary data from the National Climatic Data Center, but Dave’s calculator is a lot easier.  The National Weather Service also provides a last average frost date by location.  According to NWS, my last average frost date is March 15.

I was always confused about what the seed packet meant when it said, “plant after danger of frost has passed.”  I used to interpret the warning to mean that I had to wait until the 10% frost date to plant outside, but I’ve since learned that it is not necessary to wait that long.  The plants will likely be fine if I plant them around the 50% frost date, especially if I pay attention to the weather forecast for frost warnings.  The UGA cooperative extension recommends planting frost-tender plants in late March or early April (just remember to cover them if it gets really chilly).  One caveat: the soil temperature needs to be at least 55° F for most warm season crops to thrive, 60° or higher for tomatoes and okra.  To find your soil temperature, you can get a soil thermometer, or Georgia residents can check out UGA’s soil temperature map, which is one of the many tools on http://www.georgiaweather.net/.

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4 responses to “What Is a Frost Date?

  1. Your blog is FAB I am going to make my gardner read here and make sure we are pruning appropriately. I hope we’ll get to see you this weekend at the Garden Show…BUT we are going to plant our container gardens this weekend so we may have to miss it…due to gardening, bwahahahah. XO

  2. […] I know I’ve told you all about frost dates. And I know I told you that our 50% frost date in middle Georgia is March 23. I know you’re itching to get some tomatoes in the ground. But […]

  3. […] I know they’ve got them in the stores, but that doesn’t mean you need to plant them.  Our 50% frost date isn’t even until next Sunday, March 23.  Plus, the soil temperature isn’t warm enough yet.  […]

  4. […] close to 60°F?).  In general, I try to start hardening off the plants a week or two before our 50% frost date, which is March 23 in my part of Middle Georgia.  But if it looks like there will be a frost or a […]

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