All it takes is for the calendar to launch spring and the weather to show serious signs of warming up.

Then all thoughts turn to preparing the swimming pool and spa for summer action.

And that often includes draining the pool. If that's the coming scenario at your house, make this your mantra: Keep the pool water away from your garden or landscape plants.

Pool water contains chlorine or bromine, both harmful to plants. You'll see the results — leaves turning yellow or brown (the whole leaf or just around the edges) and extensive leaf drop.

If your pool was uncovered all winter but still treated with chlorine, the chlorine levels might be too high to be safe for plants. Use a pool test kit to find out what the chlorine level is before you start draining the water.

It would be best if the chlorine level is 0.4 ppm (parts per million). That's the lowest most test kits will measure.

If you had your pool covered all winter with an insulation blanket, remove it and let the pool sit for a week or two before draining it. The aim is to let the chlorine evaporate out of the water so that the levels of chlorine are quite low or non-existent. Again, use the pool kit to check before draining the water.

Drain the pool water in an open area away from shrubs, flowers and ground cover plants. When possible, also keep the water from coming within the area under the canopy spread of trees.

Drain the water slowly to avoid run-off and over-saturation of the soil. These suggestions also apply when draining spas and fountains.

In addition to chlorine, garden and landscape plants can be harmed by salts that accumulate in the soil.

These salts build up over time from the addition of fertilizers and irrigation water. Although in trace amounts (350 parts per million), salts in water supply can accumulate through the constant wetting and drying of the soil with drip irrigation.

Take a look at the area around your drip emitters and you'll likely see a white salt ring a few feet out from the emitters. As water evaporates and soil dries, salt is left behind at the edge of the wetting pattern.

Salts harm plants in two ways:

First, leaves, stems and roots can dehydrate when soil salts become so high that roots no longer can draw in water. As this occurs, even though plants are being watered, they wilt from an inability to absorb that water.

Second, when too many salts are absorbed by the roots, they may reach toxic levels, killing the plant.

Sonoran native plants are, in general, tolerant of moderate levels of salt in the soil. But most introduced-varieties of landscape plants are not. Even small amounts of salt can cause plant damage.

Landscape plants most commonly affected include roses, plumbago, hibiscus, oleander, cape honeysuckle and crape myrtle.

Citrus and other fruit trees also are affected.

Excess salts can be removed from the upper soil levels, where plant roots are, by dissolving them and flushing them down below the root zone with lots of water.

A large amount of water should be slowly applied to those plants suffering from or most likely to suffer from salt buildup. The easiest way to accomplish this is by running your irrigation for a longer period of time, say twice as long as normal.

You can also use a soaker hose to deep water where needed.

» about palms

"Selection, Planting & Care of Palms" will be the topic of this week's gardening demonstrations. Presentations are slated at 1 p.m. Wednesday at the Wilmot Library, 530 N. Wilmot Road, and at 1 p.m. Friday at the Oro Valley Public Library, 1305 W. Naranja Drive.

● John P. Begeman is the urban horticulture agent for the University of Arizona-Pima County Cooperative Extension. If you have questions, call 626-5161 to reach a master gardener.