Water is scarce and getting scarcer. Too much of the daily consumption in our watersheds is devoted to landscaping; irrigation of planted spaces is the number one use of residential water. With care, landscapes can be maintained without the waste that sends excess down the drain to the ocean. One good rule to judge a garden’s watering needs is to monitor soil moisture carefully, no matter what is planted and what the soil type may be. Here are some other handy tips:
• Deep-rooted plants such as trees, drought-tolerant natives, and other Mediterranean varieties need a deep soak once a month through the dry months, although if the weather turns foggy, they can often go much longer. The best way to tell if it’s time to water is to probe the soil and see if it still contains some moisture. Dig down with a shovel or trowel or use a specially designed soil probe to pull up a core to inspect. The soil should never be bone dry and crumble to dust, nor should it be wet enough to squeeze moisture out of. On the dry side, it’s time to water. On the soggy side, wait a few days and try again. Then use soaker hoses, low-flow sprinklers, or drip irrigation systems that deliver a small amount of water over a longer period covering the area of the drip zone. The idea is to let the water slowly travel down to the deep regions of the soil before it starts to puddle at the surface.
• Other shrubs and perennials may need water once or twice a week, but applying a thick layer of organic mulch can delay this even more. Again, take a look at what’s happening in the root zone before turning on the water. It may be useful to break up the watering schedule into two or three segments of shorter duration. This will allow the water to soak in gradually instead of running off as soon as the surface is wetted.
• Annuals grow from seed, germinating, flowering, and fruiting in a short season. Water is crucial to their early success, so start seeds in containers to get their root systems established before transplanting into the garden. Then they will need careful monitoring and watering for at least two weeks until they are established. To really acclimate them, transition to less frequent but slower water delivery over a longer time to help foster deeper root growth. Protect young plants with row covers or shade them with temporary hats of folded newspaper if the weather turns very hot or windy.
• Automatic irrigation systems can help regulate water use if carefully programmed. But as with all computer systems, they are only as good as their programmers. For more precise control of irrigation water, irrigation controllers can be fitted with sensors that sense the presence of water in the soil as well as atmospheric conditions such as relative humidity and temperature. These are readily available from local water agencies. They may even have rebate programs to offset the cost of such retrofits.