Our local market has had an outdoor display of transplants of summer vegetables, herbs and annuals since mid-February. The plants seem to sell quickly and are regularly replaced by new arrivals that are very healthy-looking; the tomato transplants have flowers and the summer-flowering annuals are already in bloom. These transplants are brought inside at night when the market is closed and when nighttime temperatures are cold-in the 40's. These heat-loving transplants have been protected at night from low early springtime temperatures that will stunt their growth and stop them from flowering. But they still suffer on cool days and will need extra care to help them recover and begin new growth in the garden.
The labels on the supermarket transplants which have been grown in controlled greenhouse conditions list only the plant name. The labels don't say that the tomatoes, eggplants and peppers won't set flowers until nighttime temps are consistently above 55 degrees and that they may need protection from cool days and cold nights for several weeks.
Cool temperatures needn't stop you from buying summer vegetable transplants early in the season. In fact, we should start our summer gardens a couple of weeks earlier this drought year with the expectation that temperatures will begin to climb in April if we don't get more spring rains. Here are a few hints to protect your summer transplants during cool weather for the next few weeks.
The following devices all retain daytime heat and release the heat at night to keep plants warm. When put in place in spring and fall, they can extend the growing season by several weeks.
Plastic water walls stand about 18 inches high and are placed around individual transplants. The tubes or cells are filled with water that is heated during the day by the sun.
Hot caps or cloches are an old-fashioned method of covering young, small transplants at night. Older hot caps were made of paper, but newer versions are made of waterproof materials that also transmit light and heat during the day.
Row covers and plant wraps come in many styles. Those made for covering taller plants such as indeterminate tomatoes are tied to tall hoops that are then staked into the soil. Temperatures under the row covers can be 25 degrees higher than the outside air which means that our late-season green tomatoes will ripen into November under the covers. Floating row covers are simply spread over transplants. Many also act as pest insect barriers. Look for row covers that offer 60 or 70 per cent light transmission.
Plant wraps can be placed around individual plants or wrapped around plant cages.