Heirlooms are hot, and not just the ones on "Antiques Roadshow."

Heirloom varieties of vegetables, flowers and fruits are popping up in gardens across the country, and lots of seed catalogs and garden centers now feature these old-time favorites. While there's no strict definition, the term generally refers to open-pollinated varieties that passed from generation to generation and have been home-grown rather than being commercially produced.

Heirloom vegetables have been garnering the most attention. More recently, antique fruit varieties (especially apples) have become hot commodities. There also are lovely heirloom flowers, from annuals such as scarlet-flowered Empress of India nasturtiums to herbaceous perennials, bulbs, and even roses.

But heirlooms are not necessarily better than modern hybrids. In fact, they may not measure up to hybrids in some characteristics, such as disease resistance. So, before you plant a garden full of heirlooms, learn about how heirlooms may be better than, equal to or not as good as hybrids.

BETTER THAN

Regional adaptability It makes sense that the fruits and vegetables best adapted to a given region were the ones selected and propagated through the years. In northern regions, quick-growing varieties that matured within the short summer were valued, while in warmer regions drought tolerance or a long production period were more important traits. Fanciers of heirloom roses have resurrected well-adapted regional cultivars by collecting cuttings at local cemeteries and long-abandoned homesites where rose plants have thrived despite neglect.

Great cultivar names

Many heirlooms have colorful, imaginative names. The Mortgage Lifter tomato supposedly got its name because the person who introduced it made enough from selling his tomato plants to pay off his mortgage. Moon and Stars watermelon is worth growing just for the celestial sprinkling of golden dots on the deep green rind. And who wouldn't want to plant Lazy Wife green beans? The name isn't politically correct, but the plant is said to be so productive and easy to pick that it doesn't need much tending. One caution: Correctly identifying heirlooms can be difficult because some heirlooms are listed under multiple names.

EQUAL TO

Flavor

Proponents of heirloom fruits and veggies say they grow them because they taste better than modern hybrids. And that's true -- in some cases. The heirloom slicing tomatoes Brandywine and Black Krim are known for their rich flavor, but I'll take a modern Honeycrisp apple over an heirloom such as Roxbury Russet any day. And sometimes other factors beat out flavor. I've grown Rosa Bianca eggplant, a lovely lavender-tinted, mild-flavored Italian heirloom, but it only produces one or two fruits per plant. So I now plant Purple Blush, a hybrid that looks and tastes much like Rosa Bianca but is much more productive.

Disease resistance

After World War II, there was a hybridization boom as well as a baby boom that emphasized increased disease resistance along with greater productivity. It's easier to find modern hybrids that are resistant to specific diseases, but there are plenty of diseases that affect heirlooms and modern hybrids alike. Experiment with different varieties to see which ones are less disease prone in your own garden.

Productivity

Some heirlooms tend to produce less fruit per plant than modern hybrids. That may not be a big deal if you only want a couple of delicious ripe tomatoes a week for BLTs. But if you want to can 20 quarts of tomatoes, a reliably productive hybrid may be a better bet. For leafy and root veggies, as well as many fruits and flowers, there's usually less difference in productivity between heirloom and modern cultivars.

NOT AS GOOD AS

No snap peas

Snap peas may well be my favorite vegetable ever. But if I stuck with heirlooms only, I wouldn't be able to enjoy this crunchy, succulent legume. While there are historical references to edible-podded "butter sugar" peas, the snap pea as we know it dates to the 1979 introduction of Sugar Snap, a hybrid derived from a likely cross between English shell peas and snow peas.

Nancy Rose is a horticulturist at the Arnold Arboretum of Harvard University. She formerly worked for the University of Minnesota Extension.