The Front Range’s mid-May average last frost date means it’s still too early to plant warm season vegetables such as tomatoes, eggplant, peppers and squash. Or is it?
Transplanting vegetables instead of direct garden seeding is one way of extending the growing season. You or your greenhouse grower typically start seed indoors 6 to 8 weeks before plants can be transplanted to the garden. Coddling plants inside when outdoor weather is still too cold gains you valuable “days to maturity” necessary for longer season vegetables to achieve the goal of producing fruit.
Another tool is in-garden season extenders. Products include Wall O’Water® (being filled with water right), Season Starter™ and Kozy Coat™. These plastic cones with water channels in the side use sound principles of physics to keep plants warm. The water absorbs heat from our abundant sunshine by day and releases it at night. Regulate the temperature in the cone by nudging the top open to ventilate on warm days and closed during cloudy weather and cold nights. Plant as much as a month early in April with these devices.
Remember that the mid-May average last frost date is just an average and can vary a month either direction. The snowy garden photo left was taken in Denver on May 24, 2002. Unless season extenders are used to minimize risk, playing the last frost average too closely can trip-up gardeners. This is why some risk-adverse gardeners don’t plant tomatoes until Memorial Day.
Keep in mind that extending the season is much more than frost protection provided by a sheet thrown over plants. It’s about keeping plants warm at night. Tomatoes in particular are markedly set back by nights cooler than 55 degrees F. They simply stop growing even though they haven’t frozen.
While growth is halted by night temperatures in the high thirties or forties, you lose valuable days and weeks in the quest for the necessary days to maturity in our short growing season. It takes plants days and even a week to resume active growth even when night temperatures warm.
Commercial plastic cones with water channels or home-rigged plastic milk jugs filled with water and circled around plants (photo with bean plant right) are valuable in extending our growing season. If you’re itching to plant early, season extenders are a must.
See the CSU Extension Garden Note on Frost Protection and Extending the Garden Season for more information.