GARDENING; HOT DAYS CALL FOR DIFFERENT APPROACH TO PLANTING.

Byline: Joshua Siskin

The moment of truth has arrived for Valley gardeners, at least where spring planting is concerned. As days get warmer and longer, it becomes increasingly difficult for young plants to establish themselves in the garden. One-hundred-degree heat could strike at any moment. Seeds especially, which need every advantage to germinate and develop successfully, should be planted today rather than tomorrow.

If a vegetable garden is in your plans, you may be wondering how to arrange your zucchini, corn, tomatoes, eggplants, chili peppers and lettuces to best advantage. Of course, you will want to place the corn at the back of your garden; otherwise, it will cast a shadow over your other crops. Keep in mind that corn must be cross-pollinated by the wind in order to produce ears - unless you want to personally transfer pollen from tassels to silks with a small paintbrush - which means that you should probably plant at least three rows of it if you want a significant crop.

Mary Lee Craft e-mailed a query concerning companion planting, an area of horticulture which, over the years, has become steeped in mystification and misinformation. There exists a notion in some quarters that by juxtaposing species or crops just so, pests will completely disappear and harvests will increase dramatically.

``Carrots Love Tomatoes: Secrets of Companion Planting for Successful Gardening'' (Storey Publications) is a best-selling book with much fascinating content. Yet its title gives the mistaken impression that precise positioning of plants is critical to their success.

Carrots will grow just as well planted next to Swiss chard, lettuce or pole beans as they will planted next to tomatoes. The point is to plant several different kinds of vegetables together so that no pests, most of which are specific to certain crops, will feel too much at home in your garden.

There is one word that sums up a successful planting scheme for a vegetable - or any other kind - of garden: diversity. Botanical gardens have fewer pests than farms because of the diversity of plant species in the former as compared to the relatively few types of plants/crops raised on a farm. In a botanical garden, the large variety of species is bound to include plant groups - such as sages, mints, daisies and legumes - which attract beneficial predator insects that consume insect pests.

Far more important than positioning of crops or companion planting is the rotation of crops, in any particular spot, from one year to the next. Often I hear gardeners complain that they cannot grow tomatoes anymore or that their pansies simply will not flower like they once did. The reason for such failures is repetitive planting of the same species (or even different species of the same family), in the same spot, year after year. Where such monoculture exists, there is a proliferation of soil-borne fungi that are harmful to the repetitively planted species. In addition, monoculture robs the soil of plant nutrient reserves since each crop has a tendency to extract particular minerals from the earth.

To eliminate the problem of soil fungus build-up and mineral depletion, rotate your crops. For example, in a four-year rotation for spring/summer crops, you could plant tomatoes in year one, corn in year two, beans in year three and zucchini in year four. You could grow all four crops every year as long as you divided your vegetable garden into four sections, making sure to annually rotate the crops in each section. To enhance soil fertility, plant legumes such as red or pink clover after your squash and corn have established themselves in the garden. You can broadcast the clover seed in between the developing crops or even underneath them. After you have harvested your edibles, allow the clover to continue growing as your next crop. Three weeks before planting your fall or winter vegetable garden, cut the clover plants at ground level and work them into the earth. Clover provides nutrients, soil aeration and even helps to keep pathogenic soil fungi at bay.

Eliot Coleman is the wise man of vegetable growing in the United States today. His two books, ``The New Organic Grower'' and ``Four-Season Harvest,'' should be in the hands of anyone who is serious about vegetable growing. Both are published by Chelsea Green and are available at most book stores.