With gardens having to be hand-watered in Maryland, and Loudoun County requiring odd-even plant-watering days, it's no secret that this is the worst drought since 1930. The situation calls for innovation to restrict water use while still keeping at least part of the garden green.

A kind of horticultural triage is in order. I'd recommend that the oldest and newest woody plants be your priority.

The most expendable plants during this water emergency are the green, leafy, faster-growing herbaceous ones, such as perennials, grasses, bulbs and annuals. They're the least critical to irrigate and save, because many of them will grow back from their roots in the spring, and they can be regrown in a short time from seed if necessary.

Older woody plants, by contrast, could take a generation or more to grow back. And, as venerable architectural elements of the landscape, they are as crucial to a healthy planet as any living elements in our environment.

I consider the most incidental herbaceous plants to be annual flowers and turfgrass, annuals because their main impact is aesthetic, and turfgrass because of the magnitude of overhead moisture necessary to maintain a lawn. Healthy turf can often renew itself from its roots, even after six to eight months without rain, but trees won't.

When determining what to water, tend first to the slowest-growing plants with the least chance for renewal, such as healthy, mature trees, which form the canopy of the garden, and slow-growing specimen shrubs. Oaks, maples, tulip poplars, dogwoods, witch hazels, viburnums and many other important deciduous trees and shrubs are now showing symptoms of drought stress, such as browning margins and yellowing or wilting leaves.

The most stressed evergreens I've seen are dwarf conifers and flowering woodland shrubs of the heath family. Dwarf conifer roots grow very slowly and take decades to reach maturity. Flowering broadleaf, heath-related evergreen shrubs are the sweethearts of the woods in our region, and include azaleas, rhododendrons, Japanese pieris and mountain-laurels. They have very shallow root systems, making them quite vulnerable.

Even if some woody plants grow leaves again in spring, the choice between replanting trees and shrubs versus seeding grass is an easy one. You can't sprinkle seeds and get a forest in one or two growing seasons. But seeds and water can give you grass in a matter of days--and your lawn back in a season or two.

Recycling Water One exception to letting your herbaceous plants go dry is your vegetable garden. And perhaps, with a little thought and effort, you can irrigate edible herbaceous plants by recycling water from elsewhere, including:

* Air conditioners. Condensers put out a steady flow of moisture. Most of that water is draining away unharnessed. Pipe it directly into the vegetable garden or collect it in a container.

* Dehumidifiers. Depending on how high it's set, a dehumidifier can collect a gallon or so of water a day, a substantial amount for watering vegetables.

* Gray water. Valerie Canada, horticulture consultant with the Maryland Home and Garden Information Center, advises that bath water, dishwashing water and the water left over after cooking pasta and vegetables can be poured around the roots of parched plants. But don't use water that contains bleach, automatic-dishwashing detergent or fabric softener.

This water also is safe to use on fruits and vegetables, said Jon Traunfeld, regional specialist in fruits and vegetables with the University of Maryland Cooperative Extension Service. Soak only the ground around the base of the plants, taking care not to wet the foliage of the plants, Traunfeld said.

Irrigation Techniques Always water slowly, almost dripping liquid into the soil. This meshes nicely with the Maryland restrictions announced this week, which call for watering gardens only with a watering can or a hand-held hose.

Keep the water source close to the ground.

If possible, use a soaker hose or drip line and lay the water into the soil just below ground level.

Early-morning watering is the best, but irrigation in the evening suffers from the least amount of evaporation. You shouldn't water midday, but even that's better than none at all.

If you have mulched with and dug in compost regularly, the soil surface will barely be cracked now; moisture will soak in immediately where it is needed, and the water will hold two to three times longer around plant roots. If you haven't mulched, you can lay compost over dry cracked soil, and it will still go a long way toward holding whatever water you can get into the ground.

For more facts, call 1-800-342-2507 to request the very informative Maryland Cooperative Extension Home and Garden Mimeo #HG85, titled "Watering Tips for Drought Conditions." Outside Maryland, call 1-410-531-1757. Or you can order it through the state's Web site, www.agnr.umd.edu/users/hgic/.

A final thought comes from a reader, via e-mail, and offers one more way to get the most from the water available. To irrigate, Marjory Olsen Olson of Northwest Washington writes that she uses clean screw-cap plastic bottles--milk, water or orange juice--for a drip system. Gallon size is best. To prepare, carefully make a hole in the bottom of each bottle, just off center, with the tip of a paring knife or a wood awl. Twist the knife tip back and forth, until you get a hole of about one-sixteenth of an inch in diameter. If the knife makes a slash, discard the bottle and start over. When the weather is hot, fill each bottle and place it on the ground over the roots at the base of a plant and loosen the bottle cap.

Water at a rate of one gallon per square foot of root zone per week. Larger plants or those in fruit, such as tomato plants, may require two or three bottles per week. This method works especially well for vegetables and herbaceous plants. If it is cool or rains, close the bottles' caps to restrict water flow. With this system, plus heavy mulch, there is little evaporation.

Lerner is president of Environmental Design in Capitol View Park, Md. His e-mail address is lernscap@erols.com