Q: We are going to have a vegetable garden this year for the first time. We have had a little bit of experience growing flowers, not a great deal. Should we buy plants from a garden center or grow our own from seeds?

A: If you can get good plants, you may be better off buying tomato, pepper, eggplant, cabbage and broccoli at a garden center. If you have a good place to grow them, such as a sunny windowsill, under fluorescent lights or in a cold frame, it may be fun to grow them yourself. At least, you'll know for certain what varieties they are and you can't always be sure of that when you buy the plants.

Sometimes you cannot find plants of the particular varieties you want and the only way to have them is to grow your own.

You can get a soilless media in which to grow the plants until they are ready to plant outdoors. Or, you can use the special plant cubes or pellets to grow them in. You can use the same technique in growing melons, cucumbers, summer squash and even lettuce, especially the very early crops of lettuce.

When seeds are planted outdoors in the ground, the big mistake many people make is to seed to thick and not thin out the plants. In other words, you can get good carrots, good beets, and good lettuce if you give each individual plant enough room to grow.

It may seem a little bit like a crime to go out there and plant 10 times as much seed as you need and then to throw away 10 plants to save one. But you have to do that if you want a really good-quality crop. You have to be brutal about it.

Q: What are some of the fine old standbys we might plant in our vegetable garden?

A: Here are recommendations of Dr. William Hepler, professor of plant breeding, and Dr. Peter A. Ferretti, professor of horticulture, Penn State University:

The most popular one is the tomato, and more and more zucchini squash is being grown. And sweet corn. There usually is lettuce or a salad crop. Possibly some radishes and cucumbers. Lettuce is very popular. Onions are popular, especially after a winter when the onion prices have been high.

There is a lot of interest in onions for the early scallions. You plant them close together and pull the early ones for scallions. Carrots are difficult in heavy clay soil, otherwise they would be more widely grown. Beets can be used first for the greens, then the roots. Eggplants are on the increase. Peppers are popular. Cabbage, broccoli, cauliflower and Brussels sprouts are big ones.

Savoy Ace, a hybrid, was a 1977 All-American award winning cabbage of the rumpled or savoy type. It matures 10 days earlier and is more uniform than the Savoy King which previously was the best variety we had.

Q: Where can I get horseradish roots? How can I propagate them? By harvesting them, you have to dig out the whole root. Do I have to plant new roots every year?

A: Horseradish roots are listed in the catalogue of Burpee Seed Co., Warminster, Pa. 18991. They should be planted in early spring. Directions for planting them will come with the roots.

Horseradish makes its greatest growth during late summer and early autumn. For this reason, harvest of the roots usually is delayed until October or early November, or just before the ground freezes. The quality is very poor if harvested during the summer.

Horseradish is best grown from root cuttings, sometimes called "sets," and new ones must be planted every spring. Sets are small or slender roots 8 to 14 inches long, that are trimmed from the main roots at autumn harvest.

These sets are cleaned, bundled, packaged and kept in the refrigerator or in a vegetable pit or root cellar until planting time the following spring. The roots should be protected from light to prevent their turning green.

An alternative is to leave a few plants in the garden over the winter for spring digging and take root cuttings at or near planting time.

When taking the cuttings, make a square cut at the top and a slanting cut at the bottom so you can tell which end is which. The bottom end must be planted down and the top end up, otherwise the cutting will never grow.

Q: What size garden would be needed to take care of a family of four?

A: It would depend on how intensely you garden the plot and how much you know about gardening. A plot 25-by-50 feet should provide enough food for three people for the growing season, but if you go in for canning, freezing and other processing a half-acre of garden may be required and that is a lot of garden.