Think of a transplant’s tender leaves as a baby’s skin; a baby sunburns quickly but an adult takes longer to burn because adult skin has had more experience with the sun. The transplants’ leaves need to be tougher, like those of an adult’s, before they will be safe in the garden.
The hardening-off process usually takes about a week. I also leave the transplants outside overnight as long as the temperature does not get below 45 degrees. Make sure to watch the moisture level in the pots; sunlight quickly evaporates the water from the tiny pots.
Buying your transplants at the store is cost-effective if you are only planting a few plants, and is a good way to begin a garden for the first time. I am planting 50 tomato plants, so starting them from seed is the best option for me.
When you buy transplants, look for healthy vegetable transplants that are uniformly green, not yellowed, and not wilted. Compare the plant to its neighbors and choose one of medium size. Plants should not be tall and skinny, but should have many branches and leaves protruding off the stem. Do not buy plants with blossoms or fruit on them; stress causes small plants to produce fruit.
Gradually expose your transplants to direct sun for a few days as described above before setting them out in the garden for a day of full sun. Try to avoid buying transplants whose roots are tightly wrapped in the shape of the container, or “root-bound.” If you have no other choices, gently tear the roots apart when you plant them to encourage the roots to explore the surrounding soil. Water and mulch them well after you plant them.
Garden centers sell transplants of almost all the summer vegetables, but our long growing season enables us to plant seeds of cucumbers, squash, zucchini, beans, okra, and any other summer vegetables besides tomatoes, peppers, and eggplant directly in the ground; this is both cost-effective and will produce the strongest seedlings. Plants would really rather grow in the same place in which they are sown instead of having to move around as they do when we transplant them.
The average date for the last frost in the Midlands of SC is around April 15. However, temperatures below 40 degrees can damage tomato plants, so to be safe, I have not set out mine, although I have begun sowing seeds of corn, beans, and squash. In my garden journal, I noted that we had a frost on April 15, 2008, which damaged the tomato plants I set out too early. We have such a long growing season here that I try to wait until late April to set out the plants. However, if you have set yours out, they will probably be fine, just watch the weather forecast, and cover them if frost is predicted.