The tomato's firmly rooted popularity. And the vegetable owes it all, some say, to Colonel Johnson's heroic act

THEY gathered on the courthouse steps of Salem, New Jersey, one summer day back in 1820 to watch a local resident defy the warnings and take his life in his hands. Col. Robert Gibbon Johnson, a renowned traveler, adventurer, and sometime plant explorer, had announced that he would eat a tomato for all to see ... a whole basketful in fact.

He had been told repeatedly that he courted death by this foolhardy act, for everyone knew that this was a poisonous fruit. At the very least, he would ``foam and froth'' at the mouth. To the surprise of many, Col. Johnson was capable of smiling as broadly after eating the last tomato before popping the first of the many red and yellow fruits into his mouth.

Even without Colonel Johnson's demonstration, the tomato would almost certainly have become the popular vegetable it now is. But his action may well have advanced the tomato's cause by several years, if not decades, in this country.

Prior to 1820, tomatoes were grown in American gardens, but purely as ornamentals. Thomas Jefferson reputedly raised them at his Monticello estate in Virginia as early as 1781.

For the past 15 years, surveys have consistently shown the tomato to be the most popular vegetable grown in American gardens by a wide margin. The most recent survey by the National Gardening Association shows that tomatoes were grown in 85 percent of US vegetable gardens , which puts them way ahead of second-place peppers, 58 percent, and cucumbers and onions, which tied for third at 50 percent each.

To acknowledge this fact, the National Gardening Bureau, the educational arm of the national seed industry, has declared 1987 the ``Year of the Tomato,'' and the courageous colonel's accomplishment is being duly noted. Some unofficial spokesmen are suggesting that a reenactment of the historic tomato-eating demonstration might be appropriate for Salem.

Two principal reasons account for the tomato's popularity among gardeners: taste and the ease of growing.

With the exception of sweet corn, no other home-grown vegetable has so much more flavor that its store-bought counterpart. Add to this the high yield of a tomato vine for the small amount of space it occupies and it seems that the tomato may hold top spot in the home garden indefinitely. Tomatoes can withstand mild abuse or neglect and still produce a reasonable crop, provided they have plenty of sun and aren't competing with tree roots for nutrients.

Here, then, are some of the basic points in tomato culture:

Sun. Select a site in the yard where there is at least eight hours of direct sun, preferably more.

Soil. Tomatoes want a well-drained soil with plenty of humus. Organic matter in the form of compost or well-rotted manure is beneficial in both heavy or sandy soils.

Fertilizers. The Garden Bureau suggests using a general purpose fertilizer, either chemical or natural, along with some additional sources of phosphate - Bonemeal, phosphate rock, or soft phosphate - for stimulating root and fruit development. At least one biologically enriched fertilizer , Tomato Booster, includes soil organisms found to be active in the root zone of vigorously growing tomato plants.

Plants. You can buy started plants in a nursery or start your own indoors in soil blocks or peat cubes, periodically transplanting them into larger containers as they grow. Always set tomatoes deeper in the soil when transplanting as they send out new roots wherever the stem is covered by soil. Still another option is to buy hardy field-grown plants from a nursery in the South.

Most of these nurseries supply large plant orders to Northern farmers only, but one I know of, Piedmont Plant Company of Albany, Ga., supplies quantities sized for home gardeners. These plants arrive in a wilted-looking state but they quickly revive and, in my garden, have done very well.

Planting. Set out tomato plants after all threat of frost is over, or else provide them with protection after dark. Plant the vines deep in the soil to help them establish a good root system. In warm regions, dig the planting hole straight down, but in the cooler North, plant them horizontally, burying roots and much of the stem just a few inches deep. This should be done because the deeper soils remain too chilly for the cold-sensitive tomato until very late in the spring. In planting horizontally, simply prop up the leafy top of the plant on a pillow of soil and it will soon turn upright and grow towards the sun.

Pruning. Tomatoes are pruned primarily to get larger fruit and somewhat earlier harvests. Alow one to three stems to grow thereafter removing any side shoots, or suckers as they are termed. Loosely tie these stems to a stake or fence. Another option is to simply let the vine grow at will, generally in a circular wire cage to support the vigorous growth. Be sure that the cage has openings wide enough for you to get your hands in to harvest the fruit. In this instance, the plant will produce many more tomatoes of somewhat smaller size. The total harvest weight will be somewhat higher than that of pruned tomatoes.

Tomatoes can be either the indeterminate vining types that continue growing and blossoming until frost, or determinate types that are more compact in size and produce most of their crops all at one time. Never prune determinate types or you will drastically reduce the harvest.

Mulching. A mulch of shredded leaves or straw spread over the soil after the weather has become good and hot is beneficial.

Watering. Water deeply once a week if the weather is dry.

Container culture. Full-sized tomatoes can be grown readily in tubs or half barrels. Choose miniature, often called patio types, for smaller containers. Use containers that are at least 12 inches, preferably 18 inches deep. A word of caution: Container-grown plants need frequent waterings and regular feeding with a water-soluble fertilizer.