GOOD AND BAD OF MAY RAIN.

Byline: JOSHUA SISKIN

Rain in May is not unheard of in the Valley, so the effects of last weekend's downpour on local gardens are somewhat predictable based on late rains of years gone by. May rain extends the flowering of annuals planted in late winter and early spring. Rain soaks the roots of plants uniformly and completely (something no sprinkler system can do), relieving plant stress by washing accumulated salts out of the root zone.

Flowering depends on mineral balance around the roots. When harmful salts are washed away, the minerals a plant needs become more available. Rain also brings nitrogen that is in the air down into the soil, where it is taken up by plants with botanically favorable results.

Late rain has negative horticultural consequences as well. Fruit trees such as plums that are flowering now could experience a smaller crop than usual due to spoilage of their blooms. A pelting rain will knock flowers off of a tree before they have been pollinated and set fruit. Even if the rain is gentle, it can stick to flowers for many hours and cause their contamination, as passing fungal spores find moist blooms to their liking, taking hold of and growing in them. Late rain also gives a boost to weed growth. Certain weeds will increase in height by as much as a foot during the week following a rain.

In the Valley, May is the month of maximum growth for perennials, shrubs and trees. Following rain, this new growth may be highly succulent, an open invitation to sucking insects attracted by the abundance of water in newly forming shoots and leaves. There are five sucking insect pests that cause trouble for gardeners: aphids, whiteflies, thrips, scales and mealybugs.

Aphids are the most common pests and are primarily a nuisance, causing serious damage on only a few of the many species that they visit.

Whiteflies are problematic on hibiscus, citrus and a host of other plants. Thrips are threadlike black and silver insects that curl the leaves of the Indian laurel fig, that ficus tree with the white trunk that is the most popular hedge tree in all of Los Angles.

Thrips also attack flower buds and petals of petunias and dahlias.

Scales, recognizable by their army-helmet appearance, thrive mostly in the shade and attach themselves to plants such as flowering maple (abutilon) where air circulation is restricted.

Mealybugs, living together in sticky, cottony gray masses, also make their appearance in stale air situations, whether on garden, patio or indoor plants.

TIP OF THE WEEK: Plant seeds. There is no more rewarding horticultural experience than to watch seeds turn into flowers. Hear this testimonial from Marshall and Sharon Maydeck of Arleta: ``In January, we planted a packet of wildflower seeds in a newly dug-up area, approximately 12 by 18 feet, in the middle of our backyard lawn area. For some time, nothing happened, and we thought we had thrown money away, but you should see the area now. Besides poppies, there are flowers of every color you can imagine. Who needs to go to Lancaster to see California poppies or to the mountains to see dainty blue and purple flowers when you can have them in your own back yard?''