Summer has not officially started yet, but it's already hot and plants feel it. Yes, it's a dry heat. A very dry heat, since we are entering a second year with below-average rainfall. A careful tune-up of your watering system is important before the full heat of summer arrives. Some readers simply replace the worn gasket at the hose bib. Readers with an irrigation system have a few more steps to take. There are five things to check: placement, quantity, flow, filter, and schedule.

Placement. Emitters need to be near the water absorbing (feeder) roots. Feeder roots extend far beyond the stem in their search for water, while roots at the base of the stem are for support. Look at the green canopy of the plant. The edges 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 or trunk needs a continuous circle of water placed 5 feet out from the stem or trunk. So check emitter placement. You may need to move or add new emitters as plants mature.

Quantity of water depends on species of plant, amount and type of mulch and soil type. The goal is for a single timer to deliver sufficient moisture to all plants on the system. For example, given two same-size bushes, rose and senna, the rose will need a greater quantity of water. You get this with either more emitters or a higher flow per emitter.

Check for size of emitter. Are they all 1/2 gallon per hour, or do they vary? Depending on the plants, you may want to change some to deliver greater volume.

Check for clogged emitters. If they are clogged with calcium buildup, clean by soaking in vinegar. If soil has clogged the emitters, try blowing it out backwards. Soil shouldn't be in a water system, so check for leaks in the irrigation system or holes in the in-line filter. Some emitters simply need replacement after several years exposure to the elements.

Flow and pressure. Is the flow or pressure consistent throughout the system? 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 there. Alternatively, there may be a leak. Look for damp spots or weeds that signify underground leaks.

Filter. Many of the newer irrigation systems have an in-line filter. It helps capture any solids that may be in the water as it comes into your system. Since new construction is a fact of life in Tucson, soil often gets into the pipes. Stop soil before it clogs emitters with an in-line filter. Filters are fairly easy to add if your system lacks one.

Many in-line filter units can be used to fertilize plants. I advise against it for two reasons. First, one size does not fit all when it comes to fertilizer. Second, in Tucson fertilizer salts can add to emitter clogging problems.

Another strange bump of piping on your water system should be a back-flow prevention device. This keeps water in private pipes from flowing back into the public water system. This is especially important if you have just added a layer of steer manure to your yard. Now mandatory, back-flow devices are often missing from older systems.

Schedule. That dreaded gray box on the wall must now be dealt with. First, check for back-up batteries -- usually a 9-volt. It is best to replace these batteries once per year, especially before summer thundershowers cause power bumps that erase programs.

Control boxes vary in complexity and available settings. Check that yours has the correct time and day of the week. Set it to deliver water just as plants need it -- at dawn, when they "wake up" and start to photosynthesize. Night watering is to be avoided for two major reasons. First, plants shut off at night so water is not needed. Second, fungal pathogens do not stop at night so water at night will help them infect your plants.

Depending on emitters, soil type, mulch, and plant species, the timer may need to be set to deliver as much as an hour of water three or four times per week in summer. One long, deep, watering is better than multiple shallow ones. Deeper water penetration encourages roots to grow deeper beneath the hot, drying surface of the soil. More about root zones later.

Jacqueline A. Soule, long-time Tucsonan, is a botanist and the director of Tierra del Sol Institute. For landscape consultation, design, or help with your irrigation system, call her at 292-0504.

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