Are you at your wits' end about watering your garden this summer? When I was on vacation recently I was particularly bothered by whether my irrigation timer was set appropriately. Then, of course, we had a record-breaking heat wave and my backyard was reported to be 110 degrees. In an effort to stave off your water worries, here are some basic guidelines on watering techniques.

Preparation To Avoid Perspiration According to WaterSavers' Irrigation Store Manager Mark Satterfield, "the best bets for planning ahead for vacation time are to 1) check your irrigation timer's clock to make sure it has fresh batteries 2) conduct a systems check by turning on your irrigation manually 3) check and replace any broken lines and 4) stay with the same sprinkler heads in your lawn so that water is distributed evenly." Lastly, check your calculations on how much you are watering. In my neighborhood we frequently ask each other how much we are watering and take the average from there; however, there is a more reliable science to watering that you can rely upon.

How Much To Water? How deeply you water depends largely on how deep your plants potentially root. Tomato roots can extend 10 inches deep while rhododendrons extend about 4 ½ inches. Fruit tree roots, like cherry, peach and plum are about 6 ½ inches deep. Young plants need approximately .30 to 7.0 gallons of water per week whereas mature native plants need between .10 to 3.0 gallons of water per week for a five foot canopy diameter tree, shrub or groundcover.

Clay Soils Plants can vary widely in their rooting depth because of differing soil textures of clay, loam and sand. In Marin, most of us fight with clay soils that take up water much more slowly than sandy soils and do not need to be watered as often. A plant in clay soil generally needs to be watered 1.5 to 2.5 inches deep and uses 1.00 to 1.66 gallons of water per cubic foot of soil per week. For heavy clays, Agrim, an irrigation dealer, advises using ½ gallon drip emitters for your irrigation needs.

Size Does Matter The size of your plants is also a big determinant on how much you water. Leafy vegetables and annual bedding plants require 6 inches to 1 foot of watering. Small shrubs, cool-season turf grass, corn and tomatoes require water at the top 1 to 2 feet. Large shrubs, trees, and warm-season turf grass will need to be watered at the top 1 to 3 feet of soil.

Confused yet? Marin Municipal Water District's Water Conservation Specialist David Iribarne puts out a regular watering schedule weekly for consumers. Calculations are done on a week-to-week basis determined by the amount of water evaporated and transpired in the soil as well as weather conditions. Watering calculations are also based upon each plant receiving 2 gallons of water per hour. For example, he noted that a 3 foot diameter canopy shrub or tree in the northern region, which includes Terra Linda, warmer areas of San Rafael, San Anselmo, Fairfax and West Marin, required 165 minutes of drip irrigation run time or 23 minutes per day for the week beginning June 30th. A 5-foot diameter canopy plant required 459 minutes during the same week. Of course, the northern region is notably the hottest region of Marin.

Watering Your Lawn Turf grass should be watered 33 minutes per week using spray irrigation in the northern region versus 30 minutes per week in the central region, which includes Corte Madera, Ross Valley and the marine influenced areas of San Rafael. "The numbers we give are meant as a reference and should be adjusted based upon microclimates around your house. Use our numbers, then if your plants look healthier, try lowering the water a bit each time until your plants look wilted, then go back and increase your water usage, " says Iribarne, "to get an accurate reading."

Ready to Can It? Determine the output of your sprinklers. Here is a trick on how to test them. Place tuna or cat food cans between your sprinkler heads. Run your sprinklers for 20 minutes and then measure how much water is in each can. If there is more than a 15 - 20% difference in what's in each can, you need to correct the uniformity of your sprinkler heads' water application.

How long should you water your lawn each week? With the recent hot weather and more to surely come here in Marin, our cool-season turf should be watered on average during August for 45 minutes each week if your hourly sprinkler output is 1 inch (determining your sprinkler output does make a difference!). For the month of September, your sprinklers should run for 38 minutes each week. Of course, always monitor your lawn on those hot days for extra precaution! If runoff or brown spots appear, start your readjustments by cutting back your number of minutes watering a bit or try watering one less day.

New Products There are also new products called moisture sensors that measure the moisture in your garden so that you can regulate your water usage. These sensors are inserted into your soil and record how much water stays there. The ideal soil moisture level minimizes plant stress resulting in healthier plants. The down side to this technology, according to one irrigation dealer, is that the moisture sensor clocks can corrode and not always work correctly.

Q: How do I save more water in my garden?

A: You can reduce a lot of water used just in your lawn by watering early in the morning and avoiding peak water consumption hours between 4 and 9 pm. Water your lawn on a different valve than your trees, shrubs and groundcovers if possible. Adjust your sprinkler heads to water only your yard, not your sidewalk. Try watering your lawn every third day to save additional water. Also look out for weeds as they compete for water with your lawn!

According to Agrifim, a landscape irrigation product company, "drip irrigation can save up to 70% over conventional sprinkler irrigation. Sprinklers tend to waste water because of wind scattered spray, evaporation, run-off, or deep leaching."

TIP OF THE WEEK: Use mulches to help cool the soil and minimize evaporation. Add drought tolerant plants to your garden. For weekly water saving tips, call the North Marin Water District at 945-1578.

This article appeared in the Marin Independent Journal on August 12, 2000.

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