I had the opportunity last week to chat with Bob Thomson, who was at the National Arboretum to tape a segment of "Victory Garden," of which he is host. Gardening fans have been enjoying his television show (WAPB-TV/Channel 22 at 2:30 on Sundays, and on WETA-TV/Channel 26 at noon Wednesdays) for years.

Asked about his "container gardening rap," he offered the following advice in his deep New England accent:

"When gardening in containers, I like to see you use a coarse soil mixture, the kind you'd buy commercially. This might contain ground sphagnum and bark. It's bulkier than seedling mixtures. On the other hand, potting or topsoil mixtures are too heavy and contain too much organic material.

"Because you're using pots, it's practical to buy this soil in bags, whereas it would be far too expensive if you're starting a new bed. The mix is, perhaps, not sterile, but largely free of disease and weed seeds, and, most important, free of verticulum wilt, which, of course, is soil-transmitted.

"I like to see you buy seedlings, rather than seeds, when container gardening. What is particularly attractive is to plant vegetables and flowers in the same pot. You might want to put a broccoli seedling in, and then surround it with petunias (which are low-growing and therefore won't interfere with the broccoli's habit of tall, bushy growth). If you're really pushed for space and you want all food-producing plants, instead of planting petunias around your broccoli, you'd put in radishes, or a small lettuce, like a Bibb."

Why plant seedlings?

"When container-gardening, time and maximum use of space become extremely important. If you start your own plants outside the garden, or you buy them ready to go in, you'll save anywhere from two to four weeks (and, in the case of broccoli, or any brassicas, six weeks), to grow something else in that garden, or container space, while the new plant is being readied.

"For example, when I pull a head of lettuce, I like to have a new seedling, perhaps a few weeks mature, to put right into that hole. In a few weeks that new lettuce seedling will be ready to pull, and I have a continuous supply of lettuce. In the Victory Garden, we rarely leave ground unused for any length of time."

Thomson is far more organized than most of us. "Well, these are the kinds of tricks that we have to pass on to gardeners so they can make maximum use of their space," he said.

"I love raised beds," Thomson said. "They are much easier to work and very good-looking. Get some topsoil somewhere. You might be able to take it from another part of your yard, or you may have to buy a truckload. Fill the bed two-thirds of the way up with the topsoil. Add peat moss. Over a hundred square feet of bed, you want about one- sixth cubic foot of peat moss. Top that with two and a half of sand, one of the most underused garden ingredients, and blend it all together." How do you know when it's right?

"After turning the soil over, assuming there is reasonable moisture, make a ball of soil in your hand. Then let it slide through your hand, pushing it gently with your fingers. If it breaks apart easily, it's just about right. If it falls in a clump, or resists your touch, it's too heavy, and probably needs more sand or peat moss. If it slides through your fingers very easily, it probably has too much sand.

"Later," Thomson continued, "you may want to take a soil sample down to a testing place (county extension offices offer this service), and see if it needs anything to balance it out. If it calls for limestone, do not use dehydrated lime, which works too quickly. The preparation of a new bed would be identical for flowers, perennials, bushes or vegetables, and even trees.

Meanwhile, he said, "by all means, use the space."