GARDENING; RAIN NEEDED TO WASH HARMFUL SALTS OUT OF SOIL.

Byline: Joshua Siskin

The recent rain came to Valley gardeners like a merciful benediction from above. In fact, we would be all the more grateful for additional rain in the weeks ahead.

Throughout many long months of near drought, we had waited for it. During this time, growth-inhibiting salts accumulated in the soil, as they always do during prolonged dry spells in our area. At a minimum, we need our annual average of 14 inches of rain to wash these salts out of the soil.

Soil is naturally saltier in the Southwest than in most other parts of the country. Southwest irrigation water is also on the salty side; the salts it contains accumulate in the soil over the course of our extended summer. Soaking winter rains are crucial to leaching or draining these salts past the most important and active plant roots - those roots found in the upper few inches of soil.

Salt is toxic to plant tissues and interferes with the entry of water and minerals into plant roots. In addition, salt is toxic to the beneficial decomposing bacteria and symbiotic fungi (known as mycorrhizae) that inhabit the soil.

One downside of the rain is that it postpones planting projects. Hold off on planting until the soil is no longer saturated with rain. At present, digging holes and backfilling them will only cause soil compaction, creating both a physical barrier to root growth and a deprivation of oxygen to the roots of your newly planted flowers, shrubs or trees. The growth of plant roots, like that of human beings, is critically dependent on a readily available supply of oxygen.

GETTING RID OF THAT WEED

Suzan Pitt e-mailed a problem encountered in trying to develop her garden. ``Oxalis keeps coming up everywhere. I put Round-Up and then Finale (a Round-Up type product) on it and after a couple of weeks it comes up again.'' Round-Up, whose active ingredient is glyphosate, kills a host of weeds, but oxalis is not one of them.

The oxalis weed (Oxalis corniculata) has a trifoliate leaf, which creates the mistaken impression that it is in the clover family. It has pretty yellow flowers and seed capsules which, when they are ripe, explode and shoot their seeds as far away as a hundred feet. The oxalis weed does not persist because it grows from a bulb or a rhizome; it endures owing to its wiry and unpullable taproot.

Any well-stocked nursery will carry pesticides that knock out oxalis. In general, people who are most knowledgeable about weeds - and most other garden subjects - will be found working in neighborhood nurseries as opposed to large discount or home improvement centers with garden departments.

PLANTING YOUR OWN PAPAYA 

Mrs. John P. Siegler of Winnetka sent me a letter concerning her papaya plants.

``Two years ago, I bought two papayas from the local market,'' writes Mrs. Siegler. ``We ate the fruit, and I kept the large seeds and planted them in the garden on the south wall of the house. The trees that sprang up out of the seeds are now 3 feet tall. They have survived frosts and 110-degree heat in the summer, so I am hoping that as they reach maturity they will produce. Am I expecting the impossible?''

It is highly unlikely that your papaya trees will produce fruit, since the seed you planted, if taken from the typical supermarket variety, are from a papaya that requires a warmer winter climate and higher humidity year-round than we experience here in the Valley.

You can still enjoy your papayas as ornamentals with their large, deeply cut leaves reminiscent of foliage found on the rice paper plant (Tetrapanax papyrifera) and elephant ear philodendron (Philodendron selloum).

Who knows, you might even get fruit, although your variety of papaya tree generally produces a crop within the first 12 months of life, by which time it has reached a height of 10 to 12 feet. It is also recommended that papayas be planted in clumps of three to five trees, since they can be either male or female (or hermaphroditic), and cross pollination is needed in order to ensure a crop.

There is another type of papaya, the Babaco, that grows in the mountains of Ecuador and is suitable for cultivation in the Valley. Unlike store-bought papayas, the Babaco is yellow in color. In addition, it is produced from clonally propagated plants as opposed to seedlings. You can acquire Babaco papayas through the Papaya Tree Nursery in Granada Hills, which is open by appointment. Call [phone].