Sweet Basil and other pleasantries

The value of basil as a culinary herb was underscored to me three years ago during an interview with Arno Schmidt, who was then executive chef of the Waldorf-Astoria Hotel. It wasn't so much what Chef Schmidt said but what I saw during that visit that impressed me so much.

In a room next to the kitchen he had installed a multitiered hydroponic unit principally for growing this leafy herb. Basil, according to Schmidt, was too valuable an herb for a hotel of the Waldorf's reputation to trust to uncertain outside supplies.

Not for nothing has basil been termed ''king of the herbs.'' While it adds flavor and zest to dishes, it also adds fragrance to the garden. On top of that, it's also easy to grow. Those who study companion planting note, too, that the presence of basil in the garden has a stimulating effect on tomatoes. In short, if anything in a garden can be considered a must, basil might be it.

If you have not done any herb growing (apart from parsley and chives, which the statisticians say almost every gardener grows) you might think of starting with basil. If you can put the herb in or alongside the tomatoes, so much the better.

Sweet Basil is the traditional culinary basil, which grows 12 to 16 inches tall, producing green leaves 21/2 to 3 inches long. Use them on sandwiches, in salads, and in a variety of cooked dishes.

Dark Opal Basil is much like its green relative but is a purple-bronze beauty that adds color to both your garden and salads.

Then there is a newcomer among basil varieties - Green Bouquet. It's a recent introduction of the Burpee Seed Company (Warminster, Pa. 18974), with some pretty useful claims to fame. When grown in a row, say as an edging to a flower or vegetable garden, it forms a compact green ''hedge'' about a foot high. That's because Green Bouquet is a minature or dwarf-type basil with small but full-flavored leaves (1/4 to 3/4 inch). As its name implies, it is a fragrant member of the basil family.

Somewhat unusual is the Lemon Basil, which gives off a distinct lemony scent whenever the leaves are rubbed between the fingers. Cut into cold or hot drinks, it adds a pleasant lemon flavor that is otherwise available only from lemon juice.

Basil grows well in sun but can tolerate a little shade. It enjoys moist but well-drained soil, so add moderate quantities of compost or well-decomposed manure to your soil. Otherwise add peat moss, along with a balanced vegetable fertilizer.

Plant seed a quarter inch deep after the threat of frost has passed. Or get started plants from a nursery or garden center. Set seedling out about one foot apart in rows or in clumps. Set Green Bouquet about 10 inches apart, because it grows almost as wide as it does tall.

After the plants are up and growing, they will appreciate a little mulch to moderate soil temperatures, maintain soil moisture, and smother weeds. In dry periods give the plants a good soaking every 10 days; do it more frequently if your soil is sandy.

Basil is also well suited to growing in pots in a sunny window or on the patio. Choose a pot 5 to 6 inches in diameter. Make up a soil mixture of equal parts of sieved garden soil, peat moss, and perlite or vermiculite, to which you should add a little balanced fertilizer. Another option is to buy a commercial potting mixture, although this can become expensive if you plan to grow more than just a little basil. Remember that plants growing in pots need frequent waterings during hot weather. At the height of summer they might require water both mornings and evenings.

Pinch out the basil flowers as soon as they appear to encourage the production of leaves, which can be picked fresh all summer long. You might also like to dry the excess. Pick the leaves and wash them, shaking off excess moisture. Now spread them out on a cloth in an airy but shady place. Don't put them in the sun, or they will lose their green color. When dry enough to crumble in the hand, crush them and place in a clean, dry screw-top jar or in a plastic pouch.

Basil also dries well in a food dehydrator or even in a microwave oven. For microwave drying, wash the leaves and pat them completely dry (so they don't partly cook). Spread out the leaves on a dry paper plate and give them a two-second burst on high in the microwave. Let cool and see if the leaves are dry enough to crumble. If not, give them another two seconds in the microwave at the same setting.

If freezing is your preferred storage system, spread shredded basil leaves on a tray and place in the freezer. Once the pieces are frozen remove the tray, place the shredded pieces in a container, and return them to the freezer. This way the basil leaves will not freeze in a lump, and you can remove just as many as you need each time you cook.