When to plant?
Taking a gamble on the weather
SPRING IS SUCH AN EXCITING TIME. We are ready for warmer temperatures and sunny skies, but it’s important not to let the emotional charge of spring get us too far ahead of Mother Nature.
When is it safe to plant warm season crops like tomatoes and peppers, warm season annual flowers, or to take our houseplants outside for the summer? To use an example close to home for me, the absolute earliest frost-free date for Jefferson County would be April 15. According to the National Weather Service, there is a 40% chance the air temperature will dip to 32 degrees on April 1, and a 20% chance on April 14. On April 28, there is a 10% chance the air temperature will dip to 36 degrees. These temperatures would cause significant damage to many warm season crops.
Soil temperature is also important to consider and can affect germination and transplant establishment. While the air temperature may warm up fast, we can still have cold days and nights, causing the soil temperature to warm up more slowly. Planting some crops before the soil warms to 60 degrees or higher can cause stunting and reduced production, particularly for sensitive crops like tomatoes, peppers, basil, impatiens and vinca. These effects often go unrecognized because they don’t kill the plant like a frost would.
The topographic variations in your area, such as river valleys and elevation of ridge tops, can also create differences in soil temperature and affect the risk of a frost or freeze.
For information on your area, visit www.ncei.noaa.gov/news/last-spring-freeze. This U.S. government website offers an interactive map that allows you to see the average dates that your specific area may dip to 32 degrees or below. Waiting until May 1 to plant warm season crops like tomatoes is a safe timeline for most of Kentucky.
SHELLY NOLD is a horticulturist and owner of The Plant Kingdom. Send stories and ideas to her at The Plant Kingdom, 4101 Westport Road, Louisville, KY 40207