Sprinkler and drip-irrigation systems can be turned on and off manually, but most gardeners appreciate an automatic timer or controller to manage the watering.

In recent years, automatic controllers have become more technologically sophisticated, with built-in features that can deliver the amount of water various plants need at precisely the time they need it. The best units allow you to take full advantage of hydrozoning--grouping plants with similar water requirements.

If you're planning to install an irrigation system or replace an old controller, check out your options.

Features

1. Multiple programs. A program runs one or more valves (called stations in irrigation jargon). If you have just a lawn and a sunny shrub border, an inexpensive two-program unit will handle the job. Most gardens have more complex watering needs and benefit from a controller that runs at least three programs.

2. 365-day calendar clock. A full-year clock lets you set the year, month, and day, giving the utmost flexibility in scheduling. Among the advantages: You can water only on odd or even days--a requirement in some water-rationed areas.

3. Water budgeting. This feature lets you adjust the run times of all stations with a push of a button, so if there's a sudden heat wave or prolonged cool spell, you can increase or decrease run times (usually in 10 percent increments) without tinkering with each program.

4. Longer run times. Run times of up to 10 hours allow you to deeply soak trees.

5. Self-diagnostic circuit breaker. It identifies a valve with an electrical malfunction while continuing to operate functioning valves. Controllers that don't have this feature can't operate any valves when just one malfunctions.

Accessories

6. Remote control device (about $150). This can turn stations or programs off and on from hundreds of feet away.

7. Programmer (about $100). You can program schedules on a personal computer, then download them into the controller.

Sources

Controllers are sold at home improvement centers, but to find the most versatile models, you'll probably need to visit an irrigation supply store. The units listed at left are also available by mail order from the Urban Farmer Store (415/661-2204 or www.urbanfarmerstore.com).

Recommended makes and models

For the greatest watering flexibility, irrigation specialists most often recommend the controllers listed below. Boldface numbers listed after the model names correspond to the features and accessories described on these pages. Prices given are for six-station units without accessories (adding more stations increases the cost).

HUNTER.

SRC (about $110): 1 (three programs; up to nine stations), 2, 6, 7.

IRRITROL.

Rain Dial Series ($145): 1 (three programs; up to 12 stations), 4, 5.

Rain Dial Plus Series ($155): 1 (three programs; up to 12 stations), 2, 3, 4, 5.

Total Control Series ($200): 1 (four programs; up to 24 stations), 2, 3, 4, 5.

RAIN BIRD.

E Class ($100): 1 (three programs; up to 12 stations), 2, 3, 4, 5.

ESP Series ($145): 1 (four programs; up to 24 stations), 2, 3, 4, 5.