IN THE GARDEN WARM WINTER, MORE PESTS.

Byline: JOSHUA SISKIN

Q: I come from Connecticut and am used to cold winters. I was always told that cold winter weather was necessary for a flowery and healthy spring garden. Is this really true and, if so, what effect does warm winter weather have on the garden?

- Sally Hines, North Hollywood

A: Trees native to cold climates flower sporadically - and may not flower at all - after a warm winter. That is why, for example, common pear tree varieties such as Bartlett, Bosc, and d'Anjou, will not flower (or bear fruit) in the Valley. Asian pear tree varieties, on the other hand, may be grown here since they do not require cold winters to flower and produce fruit. As you suggest, cold does promote a healthy spring garden. This is due to the fact cold curbs the growth of insect pests. If our winter continues to be as warm as it has been, expect greater than normal insect activity in the garden this spring.

Incidentally, in climates where it never freezes and insects are active year-round, many plants have high concentrations of alkaloids in their leaves; alkaloids, which are toxic to insects, serve as built-in pesticides in tropical flora.

Q: I live in Santa Clarita, which you know is semi-arid. However, my gardening problem is moss, which I thought only grew in moist areas. Is there anything that will kill the moss but will not harm other plant life?

- George Keene, Newhall

A: Moss can be a problem in any garden where there is an overabundance of water. Although moss is associated with shady conditions, it requires sunlight to grow and will not gain a foothold in heavy shade. Invariably, moss is found growing on soil that drains poorly.

The first step toward ridding yourself of moss is to pay attention to the source of moisture that is making it grow. Typically, mossy areas receive too much irrigation from automatic sprinkler systems. In Santa Clarita, gardens should not need to be watered more than twice a week during November, December, January and February, even if the weather is warm.

You can get rid of moss by donning rubber gloves and applying an all- purpose contact herbicide to a sponge. Brush the sponge over the moss and it should start dying within a week. Once the moss is gone, improve the drainage of your soil by adding organic soil amendments to it.

Moss is one of a number of primitive, nonflowering plants or plantlike organisms you may encounter in and around the garden. Liverworts form a thick green crust on the soil surface and, like mosses, require lots of moisture to thrive. Algae is not just green slime in a pool; I have occasionally seen sidewalks stained green at the edge of lawns that are heavily watered and fertilized.

In Santa Clarita, one frequently sees lichens growing on rocks and on the trunks of oak and sycamore trees. A lichen is a symbiotic organism, consisting of a fungus and an algae living harmoniously together. Lichens may appear white, gray, blue, green or yellow in color. Finally, mushrooms will pop up in gardens wherever decomposing organic material - in combination with ample moisture - is found.

None of these garden intruders are dangerous to the health of your plants. They are merely signs of excess moisture, usually in combination with shade, poorly drained soil, lots of organic matter or fertilizer runoff.

TIP OF THE WEEK: Plant dahlia bulbs now. Dig holes 12 inches deep, place bulbs in holes and cover with only 8 inches of well-drained garden soil. After dahlias have grown up 4 inches, fill holes to the top with soil. With 4 inches of their stems underground, dahlias will be much stronger and less inclined to fall over as they grow tall in the spring and summer months.