HOW MUCH WATER DOES YOUR GARDEN NEED???
Improper watering is the number one cause of plant failure. Knowing how wet the soil is where the plant roots are hard at work can help you determine your plants' health. Keep in mind: different plants have different watering needs. Learn those needs, then group plants together with similar watering requirements. The Sunset Western Garden Book is a good source for that information.
To determine the amount of water at the root level:
• A day or two after watering, dig down 8 to 10 inches with a trowel or small shovel, near the drip line (outer canopy) of the plant. Doing this in two or three spots would be more helpful.
• At that depth, grab a handful of the soil. Squeeze that handful. If it is muddy and watery, reduce your watering for plants that require regular (but not frequent) irrigation. If it is so dry you cannot form a clod in your hand (it turns to dust instead), increase your watering (for those plants that require moderate amounts of water).
• If you can form a dirt clod in your hand, yet break it apart with a little effort, that is probably the correct soil moisture for your plant.
• An easier, but more unreliable way to measure the water content of the soil: purchase an inexpensive (under $10) moisture meter (pictured at top). Test its accuracy by putting its probe into a glass of water. If the probe does not read "wet", choose another. Expect it to function for only a year or so.
• Battery operated moisture meters may set you back a few more dollars, but in my experience - with proper care (clean them after each use, don't leave them outdoors) - they will last many years.
• Extended, infrequent, slowly applied irrigation is the most efficient watering method. Soaker hoses or drip irrigation systems work best. Here in the Central Valley, foothills, and Bay Area, run them for 3 to 6 hours at a time, twice a week, in the summer. This is only a guideline to get you started. Adjust that timing to your particular soil type and plants.
• And, don't forget: add more drip emitters and drip lines as the plant grows, especially for trees and shrubs. Make sure to get water to the outer canopy of the plant (and beyond) where the roots travel.
And, the video: How Much Water Do Your Plants Need?