In the Garden:
Southern California Coastal & Inland Valleys
May, 2009
Regional Report

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One faucet and 3 irrigation modes: nearby under-mulch soaker hose, further away bubbler for sunken bed, and wand for individual-plant watering

Watering In Drought Times

Water is life. For plants, it's that simple. For us, however, it's expensive and potentially in short supply again this summer. And rationing looms. Proper watering is most important to ensure continued healthy growth of vegetable plants. Keeping the plant's root zone moist but not soggy throughout the growing season will enable the plant to produce a large crop of what we planted it for --food and beauty.

Improper irrigation will result in plant stress and less-than-optimum growth. Extreme over-irrigation on poorly-drained soil will kill plants by drowning their roots. Extreme under-irrigation can bring on other disorders, such as blossom-end rot, blossom drop, small-sized fruit, and lowered yields.

If in doubt about irrigation needs of your plants, dig down into the root zone to check on the actual soil moisture one week after irrigation. Free-standing water or wet sticky soil indicates excessive watering; dry or nearly dry soil signals the need for increased irrigation.

Plant foliage is another indicator. Glossy, perky foliage is desired. Matte (not glossy), droopy foliage may mean the plant needs irrigation. If it's in the evening, it may be just the result of the day's evaporation. If it's first thing in the morning, irrigation is needed immediately.

These five pointers should help you water your garden wisely.

1. One or two light waterings with a mild fertilizer when transplanting to settle the plant in, and again during the first month afterwards, will help establish it. Six weeks later, heavier irrigation is needed to encourage deep root growth. Or, preferably, if you incorporated lots of manure and organic matter into your soil before planting, the nutrition will already be available in the soil for the plant roots to absorb consistently.

2.Many plant root systems thrive within the first foot of soil below the surface, but other roots (especially tomatoes and squash) can reach a depth of four or five feet, unless the soil zones are restricted by hardpan, rock layers, or a high water table. In general, apply sufficient water to moisten the soil to a depth of at least three feet for these deeper-rooted plants. About three inches of irrigation water will moisten sandy soils to this depth. Six to eight inches is required for loam or clay soils.

3. Irrigate once every two to four weeks when air temperatures are in the 70s and 80s. More frequent irrigation is required for shallow or sandy soils or during periods of higher temperatures or strong winds. During hot, dry weather when air temperatures are in the 90s, large plants use about an inch of water in three days. Heavy irrigation may be needed once a week during these periods. During cooler weather when air temperatures are below the 70s, watering may be needed as seldom as once in six weeks.

4. If trees or shrubs grow near the garden, more frequent and heavy irrigation may be necessary to provide for all of the plants. And don't be surprised when you find lots of tree or shrub roots invading your vegetables, since they want more of that water!

5. Keeping a thick layer -- three or four inches thick -- of mulch over your garden soil to lessen the need for more frequent heavy irrigation. Organic mulches such as grass clippings or finely-chopped wood chips promote water absorption, slow evaporation, and gradually decay into nutrients for the soil, as well as moderating soil temperature and lessening weed germination. Therefore, the soil surface remains cooler, looser, and is being continually fed. Irrigation is then immediately absorbed and can easily move down to the deeper plant root zones. This means that you can apply less water and yet achieve more effective use.

The end result is healthier plants, less expenditure of time and money for irrigation, and less waste in runoff. And happy plants make happy gardeners -- you!


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