After an exceedingly cold start to the growing season, temperatures seem to be warming up to normal conditions. Before you rush to plant, take a step back and evaluate the environmental requirements of your seeds and seedlings. Planting too early could cause a major setback, prolonging harvest or even damaging the plant.
Several years ago I decided to test the rule that says celery will bolt if exposed to a string of cold nighttime temperatures. Hedging my bets, I planted well-developed celery seedlings under a hoop covered with Agribon for protection. For a while, the plants grew admirably, but then they started sending up seed stalks. Although I could still pick a few small outer stalks, the crop was ruined. The experts were right: Plant celery too early, even with protection, and you have a good chance of losing your crop.
When considering the minimum temperature requirements, pay attention to nighttime temperature as well as the soil temperature. In mid-May, my soil temperature was inching up toward 50 degrees, but it wasn’t there yet. Soil temperature is vitally important if you are sowing seeds directly into the garden. While some seeds will germinate at 50, most will not. For direct sowing of broccoli, beans, cabbage, carrots and cauliflower, Oregon State University recommends waiting until the soil temperature is 60 degrees. For warm season crops such as tomatoes and peppers, wait until the soil is warm at 70 degrees. Cornell University offers splendidly detailed growing guides for a wide assortment of vegetables. See www.gardening.cornell.edu/homegardening/sceneb771.html.
You can rush the season a bit if you are using transplants. Seedlings of broccoli, cauliflower, etc., can be set out when the nighttime temperature consistently stays above freezing. Protected under a covered hoop, these plants should do well with slightly colder temperatures. But be patient with squash, tomatoes, eggplant and peppers. Ideally, nighttime temperatures will be above 60 degrees when you set out these seedlings. Since that can be a long time coming in our northern climate, consider sheltering your plants with some form of protection, such as a covered cage or hoop. Such covers cut the severity of harsh winds and keep the temperature a few degrees warmer.
Soil temperature can vary from one section of the garden to the next. You don’t need a special thermometer to measure the warmth of the soil. The instant-read thermometer, popular for kitchen use, will do just fine. Measure to the depth you plan to plant, generally 1 to 2 inches for seeds and 2 to 6 inches for seedlings. If you like to plant your tomatoes deeply, dig your hole and then insert the thermometer to check the temperature at planting depth.
Cold is not the only problem. Rapidly warming days can mean that the cool-loving crops such as spinach, peas and lettuce will be stressed by the heat. Production could be limited and spinach and lettuce could run to seed quickly. If the sun suddenly becomes quite hot, these greens can be somewhat protected with a shade barrier of cloth or black screening. Peas and asparagus may ramp up production so much that you will need to harvest more than once a day.
If you planted too early and have stunted seedlings that are looking poor, consider replacing them. Cold conditions may not kill your transplants but can cause chilling injury, resulting in slowed or stunted growth. It will take at least five weeks before you know if production has been impacted and by then it could be too late. Check your conditions and get out there and plant.
Bev Carney can be reached at firstname.lastname@example.org.