Understanding Frost Dates

Getting your timing right will help you avoid frost damage from temperamental spring weather.

When the first signs of spring begin to appear, gardeners tend to get a little restless. Dreaming of that first fresh, homegrown salad, we’re busy planning out the garden and starting our seeds. But before you can get outside and get your hands dirty, it’s important to understand when to plant – getting plants in the ground after the average last frost date for your area is an essential first step to a successful spring garden.

The last frost date refers to the average final spring frost in your growing location. This date and temperature varies greatly depending on your state, county, elevation – and even whether you live in an urban or rural environment. Urban areas tend to heat up faster in spring due to pockets that surround cities called “heat islands.” Sometimes, last frost dates in these areas can be moved up by days or even a week, so be sure to consider your micro-climate while pinpointing the best time to plant. Getting the timing will keep your initial plantings of the season safe from cold temperatures – and get that garden salad onto your kitchen table as soon as possible.

How does the last spring frost affect vegetables in the garden?

  • It determines when the first seeds will be able to germinate – or not. Frosty spring nighttime temperatures are too cold for many types of veggies to survive.
  • It determines which veggies can be planted. Typically, spring crops like lettuce, cabbage, spinach, radishes, beets and carrots are hardy and able to withstand temperatures 32 degrees and above.  Warm-season crops, like tomatoes, peppers and cucumbers can’t withstand the cool temperatures of early spring in most environments. For these garden favorites, wait until temperatures are greater than 55 degrees in your area of the country.
  • Most seed packets, nursery tags and cultural information about vegetables will reference planting guidelines based off the last frost date. It’s important to be aware of your climate so you can plan your garden based off this information.

To find your specific last frost date, make use of the many online resources available that are periodically updated specifically for gardeners. The U.S. Department of Agriculture’s interactive Plant Hardiness Zone Map (link to: http://planthardiness.ars.usda.gov/PHZMWeb/), for example, is a great resource for locating the average annual temperatures in your region. Remember that last frost date data are based on historically averaged temperatures, however, and that there’s still a 10 percent chance that a plant-damaging frost can occur after the listed date in your region (although the chance of a killing frost is unlikely). As with most things in gardening, nothing is guaranteed.

If you keep an eye on the weather forecast and follow seed guidelines based off your last frost date, you’ll set yourself up for a bountiful spring garden – and avoid damaging seasonal frosts.