Q. I've noticed that a lot of heirloom tomato varieties are showing up in my seed catalogs. They promise better flavor, but are they worth it if they produce less? And do the heirlooms get more diseases?

A. Many of the tried-and-true heirloom cultivars of years past are indeed making a comeback. In many cases, the yields between old varieties and modern hybrids are comparable. As for the disease issue, fusarium wilt is a significant disease to which most hybrids are resistant and most old cultivars are susceptible. If you know for a fact that you have this disease in your soil, you should select resistant hybrids.

If the disease is not present, give some of these old-timers a try. They have captivated tomato lovers because of the many shapes, flavors and colors they add to the garden and kitchen. Seed from these open-pollinated heirlooms can also be saved from year to year.

Q. I just read an article in a gardening magazine stating that fluorescent bulbs used for growing transplants indoors could be kept on 24 hours a day. Aren't you only supposed to leave them on for 14 to 16 hours a day?

A. The thinking has been that one should imitate the natural light cycle when growing plants indoors. However, many people do leave their lights on around-the-clock with no adverse effect on plant growth. In fact, increased light on seedlings should encourage faster growth.

THIS WEEK'S CHECKLIST

1. Order vegetable cultivars that have resistance to diseases that have been a problem in your garden.

2. Prune grape vines. Disregard the heavy bleeding or flow of sap.

Garden tips are provided by the Home and Garden Information Center of the Cooperative Extension Service of the University of Maryland. For additional information on these questions, or if you have questions of your own, call the center's hot line at 800-342-2507, or visit its Web site at www.agnr.umd.edu/users/hgic.

Pub Date: 03/14/99