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How often should you water your plants? When in doubt, check the soil

Illustration of a golden watering can against a blue background
Different plants have different watering needs: California native plants, for example, need significantly less water than, say, roses and vegetables.
(Julia Yellow / For The Times)
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When it comes to watering plants, the best advice is simple: Water infrequently but deeply, and let the soil be your guide.

Some plants have greater water needs than others. Once established, for instance, California native plants and even some Mediterranean herbs such as rosemary and thyme don’t like much water. Roses and vegetables, however, are generally thirstier, and require consistent water.

To start, it’s best to group plants with similar water needs. For instance, don’t try to grow water-loving tomatoes and basil with rosemary, because there’s no way you can keep everybody happy, said Yvonne Savio, creator of the Gardening in L.A. blog and long-time director of the UC Cooperative Extension Master Gardener program. “You need to create different zones, so plants with similar needs go together,” she said.

The bottom line: Water deeply one or two times a week instead of short spurts every other day, said Savio and professional gardener Lauri Kranz of Edible Gardens L.A. and author of “A Garden Can Be Anywhere.”

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Even in the warmest days of summer, a good soak every three or four days is best for plants because it forces their roots deeper into the soil where they are healthier and cooler. Shallow-rooted plants are more susceptible to damage during heat waves.

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Watering edibles

Kranz usually plants in raised beds of untreated, unpainted wood (no wider than 4 feet so the middle is always within reach). She thinks drip irrigation is the best way to keep them watered. After she fills the beds with soil, she lays a half-inch irrigation hose on one end and strings quarter-inch perforated hoses the length of the bed, 6 inches apart.

During spring and summer in Southern California, she suggests drip watering three times a week for 18 minutes, then adjusting from there if the soil is too wet or dry. Don’t know how to tell? Stick your finger in the soil. If it’s consistently moist 2 inches down, your plants are fine. If it’s dry, break out the hose.

Drip irrigation on a timer gives you consistent watering, but be sure to check your garden regularly to see whether it’s getting enough water, Kranz said. You may need to water more often when it’s especially hot.

Kranz generally uses organic potting soil and compost in her beds, along with an organic mulch, which keeps moisture in the ground longer. Savio also uses lots of compost in her soil and mulch on top as well as a thin (about a half-inch) layer of coffee grounds to help keep moisture in the soil. (She collects from local coffee shops. Don’t put coffee grounds on too thickly, she said, because they can get crusty and repel water.)

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Savio has developed an effective way of keeping her extensive vegetable garden watered. She has buried 5-gallon nursery buckets, drainage holes in the bottom, between her tomatoes and other vegetables. She fills the buckets a couple of times a week so the water drains slowly into the soil.

Choose buckets with thick, firm sides so they don’t buckle, and don’t forget the drainage holes in the bottom. Bury the buckets so their tops are about 4 inches above the soil, she said, to leave room for mulch. This also makes it less likely that lizards will fall in.

Most nurseries have an ample supply, Savio said, and sell them for a nominal fee, if they charge at all.

The buckets make fertilizing easy. Add a shovelful of manure to the water or add liquid fertilizers, following the directions on the label.

Already planted your garden? Savio suggests digging holes about a foot from your plants, until their roots become visible, which may be just a few inches down. Stop digging when you see the roots, she said, and place the bucket as far as you can into that shallow hole. The water will still go deeper than surface watering and allow you to add fertilizers.

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Watering lawns

Lawns get a bum rap for requiring too much water, said Jim Baird, a turf grass specialist at UC Riverside’s Turfgrass Research Facility. The problem isn’t with lawns, he says. They keep dust down and neighborhoods cooler, thus reducing energy costs.

The problem, Baird said, is the way people water their lawns. Think “deficit watering” rather than “optimum watering” to keep your water costs low and your lawns healthy, he said.

Learn how to use your sprinkler timer, and turn off your irrigation in the cool months between November and April.

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When it warms up, water deeply in the early morning or evening for 10 to 15 minutes three or four days a week, depending on your lawn type (three days for warm-season grasses, such Bermuda; four days for cool-season grasses, such as fescue). If runoff is a problem, divide your watering time into three-minute cycles, Baird said. “Your lawn won’t be super lush,” he said, “but it will be good enough.”

If you’re planting or redoing your lawn, consider warm-season grasses such as Bermuda or buffalo grass, which need about 20% less water to stay green in hot, dry conditions, Baird said. Bermuda lawns aren’t as popular as fescue because they turn brown in winter, but there are many varieties of Bermuda, Baird said, and UCR’s Turfgrass Research Facility is developing new varieties that stay green during their dormant season.

Regular feeding of your lawn about four times a year can help reduce its water needs as well, Baird said. Grass needs nitrogen, and one of the best fertilizers is its own clippings, he said, so instead of sending clippings to the landfill, invest in a mulching mower and stop wasting that free fertilizer.

Be sure your mower blades are sharpened at least once a year, because dull blades shred and stress the grass. And be sure you are mowing to the right height — 3 to 4 inches for fescue/cool-season grasses but just 1½ to 2 inches for Bermuda/warm-season grasses.

Finally, check your sprinklers every year to be sure they are working properly. Fixed-spray nozzles of the same size are more efficient than rotary type sprinklers, but if you’re replacing or installing a lawn, Marco Schiavon, Baird’s colleague, thinks the most efficient system is subsurface irrigation, a series of PVC pipes with holes, spaced about a foot apart, 4 to 6 inches deep.

If you see brown spots on your lawn, don’t start watering more, Shiavon said. No above-ground irrigation system provides 100% distribution, he said, so it’s better to just hand-water brown spots, or give it a good drink with an old-fashioned spot sprinkler.