It's unfortunate, but this is about the end of the line for most Christmas poinsettias. One by one, the leaves fall in the days after Christmas. By mid-January, when the poinsettia seems half-dead, the plant is mistakenly tossed into the trash can.

But you may not want to concede defeat yet. Poinsettias make excellent plants, whether or not they color up for the holidays. There are outdoor poinsettias in Florida and Texas that have survived for a generation or more.

Before starting radical surgery to save your poinsettia, you may want to question why things went wrong with it.

Why did the plant drop its leaves in the first place?

Blame this on the lack of nitrogen in leaf tissue. Green leaves stay on the plant only as long as water-soluble fertilizer is applied regularly. Once you stop feeding the plant, it's only a matter of a week or two before leaves start dropping. This explains why the plant was healthy when it came home. Until then, any garden shop worth its salt would have been fertilizing the plant until it was sold.

What must you do now to save the poinsettia?

This is where you start working your own miracle. Begin by pruning the plant severely, sacrificing the colorful leaves, then growing the plant all over again. By mid-April, the poinsettia will be almost the same size it was at Christmas. About then, you'll have the option of creating dozens of new plants from leaf-and-stem cuttings. The new plants will reach humongous size in the fall, and be ready to color up in time for Christmas 1988. Other plants can be started from cuttings taken in July and late August. In all, the plant could produce more than a hundred offspring by Labor Day.

Here's how you work the miracle. Use sharp pruning shears and cut back all stems to within four or five inches of the soil. Cut through each stalk, discarding pruned parts in the trash can. Use a candle flame to quickly singe the ends of all cut stalks, effectively sealing the tissue to stop bleeding. If you don't seal the stems, a white sticky fluid will flow almost immediately, further depleting the poinsettia's energy supply.

Next, replace some of the old soil to improve plant performance. Water the pot thoroughly in the sink or utility tub, wait a minute or two, then spoon off the top inch of soil with a tablespoon. Mix a small batch of standard 1-1-1 (equal amounts of milled or compressed sphagnum peat moss, perlite and vermiculite) in a mixing bowl, drying at first so everything homogenizes. Wet it down with hot water from the faucet and spoon into the pot to replace the old soil.

Admittedly, replacing only the top inch of soil creates an undesirable soil layer, but this is still a viable trade-off considering the plant will be discarded after Labor Day. By then, hundreds of new plants will have been propagated from leaf-and-stem cuttings.

At this point, try to provide the warmest possible room temperature, with no blasts of hot air and reasonable humidity to thwart mealybugs and spider mites and the best possible bright indirect light. Here are some pointers: Temperature and exposure: Choose the brightest possible room with the warmest temperature. Put the plant in full sun if at all possible to promote steady growth; locating plants in bright indirect light compromises growth. Warm rooms favor quick recovery, so capture and retain as much of the sun's heat in the room as possible. Draw curtains, drapes or blinds on sunny days so heat pours into the room; closing the door will help stabilize room temperatures. Don't, however, put the plant next to a baseboard heater or heat register. Those heat blasts could damage it.

Humidity: Double pot the plant to increase humidity and eliminate all chances of mealybugs and spider mites. Humidity should be above 30 percent.

Watering: Keep the soil slightly moist. Touch the soil to sense the moisture level. When the soil is just starting to dry, fertilize the plant immediately. This translates to a constant feeding program, but it's needed if the plant is to grow vigorously. Use Peters' 20-20-20 water-soluble fertilizer. Mix a batch in a plastic gallon jug, label the jug accordingly, then apply liberally when your finger test says the soil needs wetting. Let the soil drain for 15 to 20 minutes in the sink.

Pruning: Growth will be rapid in ideal light and temperature, so you should be finger-pinching the new stems over the February 20-21 weekend and again on March 19-20. Take the first leaf-and-stem cuttings right after Easter, after which the stems should be pruned and growth restarted so a second round of cuttings may be taken in early July. Contrary to belief, poinsettia cuttings will root quickly if you keep them warm (78 degrees and above). In your first round of cuttings come April, you won't lose any plants. Other garden reminders:

The container of fruiting fig trees should be moved from the garage to an unheated basement this weekend. Check your watering schedule first to see if the container needs to be watered. If so, water it while it is in the garage, let it drain thoroughly, then transfer it to the basement. The fig tree will remain there for two weeks, after which it will be moved upstairs to resume growing. Details on care will come in the Feb. 6 column.

Some houseplants invariably become leggy over the winter, triggered by low light (short days, long nights), and sometimes because of errant applications of fertilizer over the darkest days of winter. Turning plants every week usually licks the problem. Leggy stalks may be pruned back now, however. Your plant sense tells you to root these cuttings, but this leggy growth is old and mature, therefore difficult to root.

Check vulnerable berry plants in the garden to make certain that frost has not heaved them partly out of the soil. Unmulched strawberry and blueberry plants are most often victimized, but may be saved if you inspect for damage now. Renew any mulch to a thickness of four to five inches.

If you withheld water from your holiday cactus after the flowers withered, resume watering the plant. Return to your biweekly schedule, but don't fertilize. If your cactus was in peak condition last year, look for a second crop of buds to develop over the next month. Check the links for the first signs of tiny buds, then increase the watering to every nine or 10 days.

Jack Eden hosts "Over the Garden Fence" Sundays from 10 a.m. to 1 p.m. on WTOP Radio (1500 AM).