Why His Garden Grows. Food that's safe and superior to store-bought is one reason; history is another. INTERVIEW: ROGER SWAIN OF `VICTORY GARDEN'

ROGER SWAIN doesn't worry about chemical residue on the apples he eats. He grows his own and knows exactly what he's biting into. Not all of us are so privileged, as we comb through mounds of produce at the grocery store, remembering recent reports of pesticides and poisoned grapes.

But Mr. Swain says concerns over food quality will persuade more people to cultivate their own fruits and vegetables, as he does. ``I haven't bought onions or squash in 20 years,'' says Swain, whose bearded face is familiar to fans of ``The Victory Garden,'' the popular PBS TV show of which he is a regional host.

Few people share Swain's passion for home-grown produce, seen in the 150 pounds of braided onions swinging from his basement rafters and the 250 pounds of squash stashed under various beds in his house. But he'll encourage anyone, no matter how inexperienced, to give gardening a try.

Swain tills a hillside farm in southern New Hampshire and carts the bounty back to Boston. Most of the produce in the supermarket is ``nothing compared to what I can grow,'' boasts the plant expert, who shares his home office with a sprawling, six-foot pandanus and a kumquat tree.

Though trained as a biologist, Swain has been digging in gardens since his teens and has recorded much of his hard-won wisdom in his new book, ``The Practical Gardener'' (Little, Brown & Co., Boston, $18.95).

Yes, pesticides and herbicides make large-scale food production economical, ``but there's a trade-off,'' remarks Swain, tromping through his house in work boots.

``For those of us who want produce cheap and whenever we ask for it, we're going to have to pay for it'' by settling for ``mediocre'' food and potential chemical hazards, he says. He pauses to introduce his coffee-bean bush and a towering, 25-year-old grapefruit plant.

Back at his desk, Swain cuts into an apple with his pocket knife. ``I picked this apple on the 15th of October last year, and it's been sitting in a cold cellar at about 45 or 50 degrees [F.]. You taste that,'' he says, handing a slice to his visitor.

It was surprisingly moist and flavorful. He applied just two sprays, he says. Sure, it's slightly soft and has a few scars. But he prefers this to a firm, flawless grocery-store apple that had been sprayed eight or 10 times with who-knows-what, he says.

``Doing your own gardening makes you much more aware of food cycles, what it takes to grow it, and what the range of food quality is.'' And if food has been sprayed, ``you know exactly what it's been sprayed with and when.''

Growing food teaches a person to be ``less fussy'' about blemishes and imperfections. ``So much of the poison that we put on our crops is not there to make the crop possible, but to make the harvest beautiful and attractive,'' says Swain. Bananas, for example:

``There is no known insect that can pierce the peel of a banana,'' he says. All the insecticides sprayed on bananas are to prevent blemishes on the skin.

Then there's peas. A bag of generic-brand peas costs less, though the peas are not uniformly sized, like name-brand peas.

``Ever picked peas?'' he asks. ``They're different sizes, aren't they? Bother you a whole lot?''

People would probably enjoy more kinds of vegetables and fruits if they had actually tasted the ``real'' thing, says Swain. A store peach just won't compare with a fresh-picked peach. Why? Because store peaches are picked green, he says, to get them to the market in time. Picked prematurely, the fruit cannot ripen the same way it can on a tree - it's a biological fact.

``Tomatoes will soften and turn red,'' he says, ``but they will not match the flavor of vine-ripened tomatoes.''

Get away from the notion that all foods should be available at all times, says Swain: ``My life is shaped by the agricultural calendar. I have asparagus for six weeks every year and during those six weeks, do I eat asparagus! It's fresh, it's `free,' and I gorge myself on it. Then it's just fine if I don't eat it for a while. To the supermarket shopper, the stuff is always available - and always mediocre.''

FOR gardeners, every harvest involves a celebration of some kind, too. Turnips, onions, and squash usher in Thanksgiving. The tail end of the rhubarb season overlaps with the beginning of the strawberry season, ``so you put them in a pie together!'' People who grow their own food are accustomed to such seasonality and appreciate it, Swain remarks.

Unfortunately, it's not very feasible to grow all your own food, says Swain. It is possible, but the trick is being able to store it. Canning and freezing are a lot of work - and one would still have to buy the ``big ticket'' items, such as meat, as well as dairy products and grains.

Then why garden?

``It's meaningful work. ... There's something magical about it. The ability to harness plants is, in effect, the ability to capture the energy of the sun,'' he says. All cultures, in all times and places, have done this. ``When I grow corn, I'm tying myself into a great tradition. I'm picking up the echoes of agricultural history.''

Despite a growing interest in gardening in the United States, ``we don't have the books, the garden centers, the gardening contests, ... and the educated labor pool to help us out,'' he explains. And let's face it: ``Gardening is hard work. You get tired, sweaty, and dirty.'' Young professionals hardly have time to water house plants, let alone cultivate cucumbers.

``We're never going to make gardening easy,'' he says, but we can make it less hard.

Start by recognizing how much work something is going to be ``and then pace yourself accordingly,'' says Swain. ``If you're exhausted, try keeping a smaller garden.'' This year, ``The Victory Garden'' will focus on container gardening, window boxes, and gardening in locations that initially seem a bit small, he says.

One time-saving device, he says, is ``just good plain common sense, like lawns ... I keep mine mowed, but I don't fertilize it. The more you fertilize, the more you mow.''

He doesn't water his grass, either; he lets it go brown.

``What happens to grass in its native land - in the prairies of the West or the savannas of Africa? It goes brown. Grass is supposed to go brown.'' It doesn't die, it just goes dormant. ``You'd have to have a drought that lasted for years to kill grass,'' he says.

His neighbors don't seem to mind, he adds.