IN THE GARDEN DRIP IRRIGATION ARGUMENT HOLDS MORE WATER.

Byline: JOSHUA SISKIN

Q: My husband and I have a running argument regarding the best method of watering. He insists on putting his thumb over the end of the hose and spraying all pots and plants from above. I am of the belief that it is better not to wet the foliage and water only around their base. By the way, his method is also hard on my windows.

- Renate Colvin

Northridge

A: As a general principle, it is better to water from below than above since plants take up water through their roots and not through their leaves. One of the reasons conventional spray sprinklers are inadequate is because the spray is blocked by the foliage of surrounding plants and does not reach and infiltrate the soil where it can be absorbed by roots. Drip irrigation is better than conventional irrigation not only because of the enormous water saving involved, but also because drip emitters may be placed precisely where a plant's root zone is found. Coincidentally, the so-called drip line of a plant or tree coincides with the most suitable location for drip emitter placement. The drip line is where water drips off foliage during rain. It is an imaginary circle on the soil surface that corresponds to the outside foliage perimeter. So place your drip emitters under the outside leaves of your shrubs and trees, and never next to the trunk. A plant's drip line is where its most actively growing roots are located.

Where container plants are concerned, it is a lot easier to water from below with a water wand (topped by a shower-head type nozzle) attached to your hose. A water wand is several feet long with a shut-off valve at the base. This valve allows you to control the flow of water through the wand. You can even shut the water off completely as you move from one container to the next. Water wands can be found at any nursery or home center with prices ranging from $10 to $20.

There are certain circumstances, however, where it is desirable to moisten the leaves of a plant. This is especially true with interior, tropical specimens. Plants whose origin is the equatorial rain forest will clearly feel more at home where the humidity is elevated. Humidifiers are increasingly common among indoor plant enthusiasts. There are even mini-humidifiers that may be used discreetly for single plants. Both indoor and outdoor plants will benefit from having their leaves cleaned or washed occasionally, especially in windy or dusty environments. A layer of dust attracts spider mites and other pests. With indoor plants, use a slightly damp cloth or leaf polish for cleaning.

If you mix Miracle-Gro or a similar product into a hose-end sprayer, watering over the leaves is beneficial. In ways that are not completely understood, liquid fertilizer is absorbed through foliage. Commercial growers of vegetables and fruit trees have seen increased yields as a result of overhead liquid fertilization, also known as fertigation, and ornamentals flower more prolifically as well.

Roses benefit from overhead irrigation in another way. Spores that cause mildew settle on rose bushes at night and may begin to grow on dewdrops that make their appearance in the early morning. A strong spray of water over rose foliage in the morning will knock off the mildew spores which, unhindered, can develop into a noticeable woolly white film before the day is through.

TIP OF THE WEEK: Where you have many container plants, it is a good idea to cluster them in groups. Your plants will benefit from this activity, protecting one another from excessive heat, wind or cold and - through the loss of water through their leaves - provide each other with an extra measure of humidity in the surrounding air.