It is important to plant your garden seeds and transplants at the right time and the key is knowing when your area will see its last spring frost. Some garden plants taste even better after a little frost. Cool season crops such as cabbage, broccoli, lettuce and kale can tolerate a light frost and will grow best when sown a couple weeks before the last spring frost. Peas and spinach, are so cold-hardy they can be planted “as soon as the ground can be worked,” which means that if the dirt is not frozen and you can get them in the ground go for it! For us, that date is around St. Paddy’s Day.
Warm season crops (i.e., squash, cucumber, and basil) will be killed by frost if your seeds come up too soon. Transplants (already started plants) such as tomatoes, peppers, and eggplants will be lost in that last annoying frost if set out too early. Heed the warning on seed packets that say, “Plant after all danger of frost has passed.”
Finding the average last spring frost date for your specific area may take some research.There are many U.S. maps that show last frost dates however it is hard to find your exact location dates. The best source is the National Climatic Data Center web site. Choose your state and nearest city. The site will show your average last spring (and first fall) frost dates, based on weather data collected by the National Climatic Data Center from 1971 through 2000 from that location. You can choose to plant between a 50/50 probability of frost after the given date, or play it safe and choose the 10%date, which means there is only a 10% chance of a frost after that date.Another great tool to find your average frost dates is the MOTHER EARTH NEWS Vegetable Garden Planner web site. The Planner will send you customized planting reminders for which crops need planting based on your frost dates and location.
Our west central Ohio50/50 probability frost free date is April 16th, however, I never trust that date. I am not going to chance losing my transplants by putting them out to early. Most warm weather seeds will not germinate in cold soil so waiting a week or two will not only help with germination but lesson your chance of having to scramble for grandmas old sheets to throw over your baby plants. We plant our transplants on Mother’s Day; if we are having a very warm year and the soil is warm I will direct sow seeds a week before planting transplants.
Very early spring (as soon as the ground can be worked)
After last frost date
Light freeze (frost) – 29°F to 32°F—tender plants killed, with little destructive effect on other vegetation.
Moderate freeze (frost)– 25°F to 28°F—widely destructive effect on most vegetation, with heavy damage to fruit blossoms and tender and semi-hardy plants.
Severe freeze (frost)– 24°F and colder—damage to most plants.