Knowing when to harvest garden crops is as important as knowing when to plant them. If you catch them at the right time, you'll get accustomed to eating vegetables at their best, a circumstances shared by only two groups of people in our civilization - those who can afford to pay any price for the best, and those who can pick it in their own backyards.

Beans are a good example. Most commercial growers won't pick them small, except for specialty markets. They weigh more when they're big, but they taste so much better small and slender that most gardeners prefer them that way. And their constant picking keeps their plants producting.

Beets are better picked young too. They're sweeter and more tender. If you start by planting them thickly, and then in succession, you can eat baby beets all season and still grow big ones for storing in the fall.

Broccoli is picked before the buds begin to open into flowers. Cut the first head on a long stem and smaller heads will form in the leaf axils for much of the season.

Cabbages are ready when the heads are big and solid. If too many reach that point at once and some of them look near to bursting in a hard rain, you can sometimes prevent it by cutting some of roots so the cabbages can't take in so much water. Then use these first.

Carrots can be harvested any time they're big enough to eat. Baby carrots are so delicious, too, that it's often worthwhile to plant extra space in carrots just so you can eat a lot of them young.

Cucumbers can also be picked any time they're there. You can take them small as gherkins or let them grow green and long, but they're best before the seeds get tough. If you let them get fat and yellow on the vine, they'll slow down production.

Eggplant, too, can be eaten big or small. Italians grow some that are only four inches long and usually cooked whole. Let them grow as large as you like, but remember that picking them gives the plant energy to produce more.

Herbs to be dried are harvested just before flowering for maximum flavor, but they can be harvested throughout the season for table use.

Leeks aren't harvested until late in the season - they take about 120 days to reach maturity. Lettuce can be picked as young leaves or allowed to grow until heads fill out. If lettuce starts to get tall, though, it gets bitter too.

Muskmelons and cantaloupes are ready when they just about fall off the vines and when the stem end is fragrant. Watermelons are harder to judge. A ripe one is often yellow on the bottom, and should have a hollow sound if you knock on it.

Onions and shallots are ripe when the tops have turned brown and died down. Some people knock them down in July to make this happen faster, but it's not necessary. They'll do it on their own, and keep better for the extra time.

Peppers can be picked any time they're worth eating. You can pick them small and green or let them get big and ripe. It's just a question of how you like your peppers pickled.

Potatoes are delicious small and new - and, if you grow them under a hay mulch, it's easy to find them that way. New potatoes are one of the great joys of growing these tubers - every dish is a special event.

Squash varies in harvest time. Zucchini and patty pan types are best picked when young, while you can still scratch the skin with a fingernail. That way they need no peeling, and you'll be keeping the bushes booming too.

Winter types, on the other hand, aren't picked until the rinds have gotten hard. These require a longer season than summer squash.

Tomatoes can be enjoyed at several stages of development. Early in the season, they can be picked big, but green, and battered and fried. they can be picked just before they're ripe and ripened on a windowsill. In heavy slug territory, it's sometimes impossible, but tomatoes are still best ripened on the vine. Then they're so red and juicy they sing a song of summer, and let you know exactly what it means to enjoy garden produce as its best.