If you still have your poinsettia from last Christmas, the time has come to start the process that will cause it to bloom again this year.

The poinsettia is a "photoperiod sensitive" plant, which means it begins to set buds and produce flowers as nights become longer. The key point now is to see that the plant is dept in uninterrupted darkness for 14 continuous hours per day, starting right about now and continuing until about December 15.

This can be accomplished by putting the plant into a dark closet at 6 o'clock every evening and leaving it there until 8 o'clock the next morning. Or you may put a cardboard box over the plant for 14 hours using the schedule above.

The reason for the darkness is that without it the plant will not set a bud and produce a flower.

Ordinary light in the evening will prohibit development of this physiological phenomenon. If the light is turned on for even a few seconds, the plant will not bloom. The night temperature during this dark period should be 60 degrees to 65 degrees F. If the temperature is higher than that, the setting of buds may be delayed or halted.

Night temperatures can drop to 55 degrees. During the day avoid heated rooms above 75 degrees and especially low humidity. Temperatures below 50 degrees, chilly drafts, heat from the TV or other appliances can cause leaves to drop.

Between 8 a.m. and 6 p.m. they do best in an area with lots of daylight such as a window -- any window. However, avoid direct sunlight and extremely cold or frosted window panes.

Keep your poinsettia moist. Test the soil surface with your finger. Add room-temperature water when it feels dry. Water until water comes out through the drainage holes at the bottom.Wait 15 minutes for excess water to drain and empty the saucer.

Those bright-colored petals on the poinsettia aren't really blooms at all: They are actually leaves at the top of the plant that turn color and are called bracts. The real flowers are the clusters of yellow and green buttons in the center of the bract.

Today's highly improved poinsettias are much more satisfying and longer-lasting than they used to be. Poinsettia breeders have had tremendous success during recent years in developing much better varieties, growing them in many different sizes and shapes, and in shades of red, pink, white and marbled colors.

But these new varieties still require good personal care. If you aren't successful this year, buy a new plant for Christmas and try again next year. Q: Bees are swarming in the ground of my garden. Can you advise what to use to eliminate this nuisance? A: yellow jackets and wasps sometimes build up large populations during the summer. They are dangerous particularly to persons allergic to any kind of sting. Do not swat or otherwise fight yellow jackets or other bees and wasps that happen to be buzzing around you. They will usually go away if left alone. If not, walk under a shelter and the insect will not follow. Do not wear bright colors, hair sprays, perfumes or take food outside when they are around. If you are stung by several, it's wise to see your doctor right away even if the stings appear to go away and there are no immediate complications. To control yellow jacket wasps, first locate the nest. You may be able to find it by watching them go to it in late afternoon. After it gets dark, spray the nest with sevin or spectracide. The yellow jackets die each fall, except the queens. Q: Our Christmas cactus bloomed beautifully the year it was given to us, but last year it didn't bloom at all. How do I make it bloom? A: It meeds a month of long nights (13 hours) of uninterrupted darkness with temperatures of 55 degrees to 60 degrees F. at night to initiate flower buds, starting in early October. After flower buds form, length of night is unimportant. It will drop its flower buds if they are exposed to cold drafts, or the plant gets too much or too little water, or rough handling.Q: I have tried several times to transplant a small pine tree from the woods to my yard. What is the secret of success? A: Even small pines growing in the woods usually have long, straggly root systems, and it's almost impossible to dig one up without leaving most of the roots behind. Then, too, a small pine in the woods may be anywhere from two to 40 years old. On the other hand, one or two-year-old seedlings grown in a nursery are easy to transplant successfully.If you must take one from the woods, root prune it six months in advance or try taking two or three that are only two or three inches in height. Q: My mother has a pink dogwood in her front yard, the most beautiful one I've seen. Can I take cuttings from it and start one for myself? A: Pink dogwood cuttings can be rooted under intermittent mist in about 30 days. Cuttings should be taken in early summer. Keeping it alive through the first winter can be quite a problem. Q: I live near a noisy highway and would like to plant a shrub and tree barrier to reduce traffic noise. Where should this screen be planted to be most effective? A: Plant the trees and shrubs as close to the noise source as possible. Use shrubs six to eight feet tall next to the traffic lane with backup rows of trees 15 to 30 feet tall. A 20- to 50-foot-wide belt of shrubs and trees is desirable. Q: I love pansies and plant them every year. When hot weather comes in late spring, they always fold up. Is there a variety that can persist despite hot weather? A: Imperial Blue, a 1975 All-America winner, has unusual heat and humidity tolerance. It keeps on blooming from early spring all through summer and well into late fall. Seed of Imperial Blue should be available for purchase at most large seed stores and from mail-order houses. Q: Should I cut off the tops of my asparagus or leave them on through the winter? I've heard conflicting opinions about this. A: It is a good idea to leave the tops on all winter and cut them off in the spring and mix them with the soil through shallow cultivation. Q: I've been told that Epsom salt is good for roses. Is this true? A: A study sponsored by Dow Chemical Co. showed that use of Epsom salt would help roses growing in magnesium-deficient soils. Better have your soil tested first before using it. Q: My large oak tree has had an abundance of acorns every year for many years, but this year seems to have none. Is that a bad sign? A: It may be an indication of low vigor of the tree. Fertilizing it generously with 10-6-4 fertilizer in the spring should improve vitality, if that is the problem. Q: We've been told not to remove the clippings when we cut the grass on our lawn.If left on, won't it lead to thatch? A: Lawn-grass clippings are basically 75 to 85 percent water, and about 3 to 6 percent nitrogen, 1/2 to 1 percent phosphorus and 1 to 3 percent potassium (potash), along with calcium and a few other nutrients. There is little or no lignin or cellulose in turf-grass clippings, and because of this along with their being mostly water, they do not lead to thatch accumulations. Research has shown that grass requires up to two extra pounds of nitrogen per 1,000 square feet when clippings are removed. Q: When is the best time to fertilize our lawn? A: Almost all of the 12-month fertilizer needs of Kentucky bluegrass, fescue and perennial rye should be applied in the fall, according to specialists. They need from two to four pounds of nitrogen, and one to two pounds each of phosphate and potash per 1,000 square feet. The amount of fertilizer to use should be determined by its nitrogen content. For example, five pounds of a fertilizer containing 20 percent nitrogen will furnish one pound of nitrogen. Apply 1 to 1 1/2 pounds of nitrogen per 1,000 square feet now, repeat four weeks later, and make a third application in December. No more fertilizer should then be necessary until late in May when about a half-pound of nitrogen per 1,000 square feet may be needed to give the lawn a more desirable color. Q: Our wisteria is getting out of hand. Can it be pruned and its growth confined to a small area without too great a loss of flowers? A: The Chinese wisteria can be pruned rather severely and will bloom as well or even better because of it. The Japanese wisteria blooms much better if left unpruned. The flowers on the Chinese open before the leaves appear; on the Japanese the flowers develop with the unfolding leaves. Q: The leaves on my African violet seem to become smaller and smaller and very hairy in the center of the plant, and the plant no longer blooms. What could be wrong with it? A: The plant probably is infested with cyclamen mites. Tiny and almost invisible, they hide in crevices and buds and feed on the growing tips. Submerge the whole plant into water that has been heated to 110 degrees F. and keep it there for 15 minutes. That should get rid of them.