Achieving a Long, Abundant Harvest
Start early. Seed packets encourage starting the seeds indoors even before conditions are optimal for the plants outdoors; this is a great way to get a jump on the growing season. Follow planting directions and start the seeds in pots with clean potting mix or well-composted soil. Keep them moist; you can even water with warm water and then cover the pots with plastic wrap if you're starting plants like peppers or tomatoes which sprout best with some heat. For vegetables that don't transplant well, like carrots and lettuce, wait until daytime temperatures are warm enough for sprouting, direct-seed into the ground, then keep the soil warm at night by covering the area with plastic wrap.
Practice hospitality. Plants get their energy from the sun, but they need essential minerals and other elements from the soil. If the ground is loose and fertile, the healthy plants can more readily fight off pests and other stresses, and concentrate on flower and fruit production. Every few weeks, treat the roots with a little compost tea, or whenever the bottom leaves start to yellow, which signals a need for more nitrogen.
Show kindness through "cruelty." It goes against the grain of the nurturing gardener to have to harm or kill anything in the garden, but better yields require that plants put the majority of their resources toward making produce. If seedlings are too close together, thin the crop by snipping some of them with garden scissors. The remaining plants will produce more food than if all had survived, but couldn't thrive. Some plants overdo their foliage, like tomatoes, which produce "sucker" branches between the main branches. Remove these, and the plant will be able to generate more flowers instead of having to support all that extra greenery.
Pick diligently. Many gardeners don't bother to collect if they don't see enough of something to make a whole meal, but this is a mistake. First, a little of this and a little of that is usually enough to make a whole stew; don't waste anything! Second, some plants, like peas and beans, stop making more flowers if enough pods mature sufficiently on the vine. Try to pick every two days or so; the plants will have to put out more to keep up with you.
Tuck plants in at night, once the growing season starts to wane. Temperatures fall, especially once the sun goes down, but you can retain some of that daytime heat and keep the harvest going a little longer by covering the plants. Nurseries sell lightweight, gauzy row covers for this purpose, but the materials need not be so specific. Just about anything translucent, from plastic tarp to wax paper to milk jugs can cover a row or individual plants to keep them warm enough to ripen their last vegetables. Structured covers like cold frames, greenhouses, and cloches work the same way.