Irrigation tips for Southwest lawns and gardens
by Jacqueline A. Soule, Ph.D.
The Irrigation Association designated July "Smart Irrigation Month" to promote efficient watering practices, technologically advanced irrigation products and water conservation. In other words, let's get smart about irrigation, especially here in the Southwest.
Most homeowners overwater their landscapes or waste water through inefficient habits. When, in effect, there are three keys to smart irrigation: placement, quantity and timing.
Placement: However you water — hose, drip emitters, soaker hose or watering can — water must be applied near the roots of plants. Feeder roots extend far beyond the base of the plant in their search for water. Roots near the trunk are for anchor and support and don't absorb water.
Look at the green canopy of the plant. The edge of the canopy, where a light rainfall would drip off, is where the feeder roots are. A tree, shrub or groundcover with a canopy 5 feet out from the stem needs a circle of water placed 5 feet out from the stem. So check water delivery sites. You may need to move things as plants mature.
Quantity: The amount of water a plant needs depends on species, season, depth and type of mulch, soil type and cultural care, such as fertilizing. One long watering is better than many quick ones.
Deep water penetration encourages roots to grow deep beneath the hot soil surface. Ideally, water 3 feet deep for trees, 2 feet deep for lawn and shrubs, and 1 foot deep for small perennials and annuals.
To check depth, water for 15 minutes and use a soil probe (or a knitting needle) to test your soil. Multiply the inches the probe easily sinks times four to get how deep the water goes in one hour. Then you can gauge how long you should water.
If you have a drip system, is the flow or pressure consistent throughout? Place buckets under emitters at the beginning, middle and end of your system. After 15 minutes, stop the flow and measure. Did the one gallon per hour emitter deliver a quart? You may need to use larger emitters at the tail end of your system to get adequate water to the plants growing there.
Timing: Water just when plants need it — at dawn. Dawn is when plants wake up and start to photosynthesize. Most plants in the sunny Southwest turn off photosynthetic systems around 10 a.m. in the summer. Avoid watering at night because plants can't use the water at that time, but fungal pathogens can.
If you have an irrigation control box, you must change the irrigation program quarterly as the seasons and plant water requirements change. Control boxes vary in complexity and available settings. You'll save money in the long run if you take the time to learn how to take care of this task.
A good landscape professional should be able to coach you on how to use your system. Also, check for back-up batteries. It's best to replace these batteries once a year, especially before summer thundershowers cause power bumps that erase programs.
These water-wise irrigation habits will result in a healthier landscape, conserve water, plus reduce your water bill. Now that's smart!
Jacqueline Soule is a garden writer based in Tucson, Ariz. She has lived and gardened in almost every U.S. Department of Agriculture zone from 2A to 9B. Everywhere she's lived she's striven to make her yard a haven of serenity.