What do you think of when you see the word “heirloom” associated with tomatoes? I used to think they were old varieties that were probably especially tasty but finicky to grow.

Well, part of that is true. Heirlooms can be old and are usually very tasty, but they’re not finicky.

Heirloom tomatoes come in a variety of shapes, sizes and colors, including red, purple, green, yellow and orange. Some even have hints of black or multiple colors on a single tomato. With enough space, you could grow long, tapered green tomatoes; round yellow ones; and large, beefy, ridged purplish-red ones.

But it’s generally the taste that captures a tomato lover’s fancy. Some heirlooms are as sweet as candy; others have a fruity, acidic bite. The flavor of garden-grown heirloom tomatoes is vastly superior to those tough-skinned, mealy, tasteless things sold at supermarkiets in winter. 

There is no widely accepted definition of an heirloom fruit or vegetable. Some say heirlooms are varieties that are more than 100 years old. Others say 50 years old. Still others argue that heirloom varieties are those that existed before 1945, when seed companies began to develop hybrids.

In my view, a tomato variety qualifies as an heirloom if the seeds have been handed down from generation to generation to safeguard the variety’s desirable qualities. Heirloom seeds are open pollinated and not genetically modified. Open pollination means that  insects, birds, wind or other natural mechanisms effect pollination. As long as other varieties are not located nearby, open-pollinated varieties will remain consistent from one generation to the next.

To grow your own heirloom tomatoes, you need an area that receives full sun. Tomatoes also like well-draining soil with plenty of organic matter to allow moisture and air to reach the roots as they grow.

Do not overfertilize. Too much nitrogen produces large, leafy plants but little fruit. Add bone meal when the plants begin to blossom. The bone meal will increase flowering and help prevent blossom end rot, a disorder in which a brown patch develops on the bottom of the fruit.

Be alert for tomato hornworms. These long green caterpillars chew up the leaves and hide under the foliage during the day.

Consistent watering is essential. Heirloom tomato skins tend to be thinner than their hybrid counterparts and may split if the plants are irrigated sporadically or drenched with rain after a dry spell. In that event, the inner flesh may expand faster than the skin, producing cracks.

Some heirlooms reach six to eight feet in height. Be prepared with cages or tall stakes to help the plants support their offspring. If you like large tomatoes, select a few widely spaced blossoms and remove adjacent clusters to force the plant to concentrate nutrients on fewer tomatoes.

It’s too late to start tomatoes from seed for this summer, but you’ll find plenty of heirloom seedlings at your local nursery. Ask the nursery staff for help in choosing varieties with the qualities you’re seeking. Some popular heirloom tomatoes include ‘Brandywine’, ‘Cherokee Purple’, ‘Big Rainbow’ and ‘Mortgage Lifter’, appropriate for the present economic climate. Plant them now, nurture them and wait for harvest time.

At that point, you can enjoy them sliced on a platter with fresh mozzarella, olive oil, balsamic vinegar, basil, salt and freshly ground pepper. Or cut up in a green salad. Or stuffed with breadcrumbs, rice and herbs. Or layered on sourdough toast with lettuce and applewood-smoked bacon to make a delightful BLT.

If you can’t grow your own heirloom tomatoes, watch for them at the farmers market.  A culinary delight is awaiting you.

 Napa County Master Gardeners (http://cenapa.ucdavis.edu) are answer questions Monday, Wednesday and Friday, 9 a.m. to noon, at the UC Cooperative Extension office, 1710 Soscol Ave., Suite 4, Napa, 253-4221. E-mail garden questions by following the guidelines on the Web site.