The poinsettias this season are much better plants than those of a few years ago. With proper care they should stay attractive for a long time.

The plant's small yellow flowers are inconspicuous. It's the red, pink or white leaves or bracts that have made it a symbol, along with the Christmas tree, of the Christmas season.

Protect the plant from bruising and chilling. Exposing it to temperatures of 50 degree F. or lower is almost certain to cause the leaves to wilt and the flower bracts to drop. It needs good light, but keep it away from a cold windowpane.

The best temperature for the poinsettia during winter is between 70 degrees and 75 degrees during the day and at 60 degrees at night. Don't put it near the radiator or TV set where warm air can damage it. Keep it out of drafts because they can increase water loss, causing leaves to drop.

When the soil appears light in color or feels dry to touch, water it with room temperature water. If the pot is wrapped with plastic foil, a hole should be punched in the foil to permit excess water to drain away. Excess water prevents air movement through the soil and the roots die from lack of oxygen.

Water until water comes out of the drainage holes, wait 20 minutes for excess water to drain, and empty the saucer. If the pot stands in water very long, the roots will be damaged. Check the plant daily to see if it needs watering.

This year plants of the poinsettia named for Amy Carter, daughter of President and Mrs. Carter, will be on sale. It was developed by Gregor Gutbier, a European horticulturist, who began to hybridize poinsettias in the early 1960s.

Gutbier contacted Paul Eck Sr., in California, as the most respected man in the poinsettia industry. Eck, impressed with Gutbier's description, flew to Germany in early 1976 to see the new plant. He was impressed and negotiated right there in the greenhouse with a handshake.

Eck named it Amy in recognition of the President's conservation efforts and as a tribute to our nation's children, who like Amy and her generation will need all the encouragement they can get to face the challenge of conservation.

Amy is a long-lasting variety, tends to be shorter and bushier rather than tall and produces many branches, giving it a bouquet form with more flowers. Q. I still have my poinsettia from last Christmas. It has lots of green leaves but not a sign of a bloom. Isn't it supposed to bloom for Christmas? A. The poinsettia won't set buds and bloom unless kept in darkness for 14 continuous hours daily starting about October 1 and lasting until early December. The night temperature during the dark period should be from 60 to 65 degrees. If the temperature is too high, setting of buds may be delayed or halted. Better luck next year. Q. I have succeeded in rooting the top of a pineapple. Can you tell me how to take care of it? A. Plant it in a six-inch pot, give it full sunlight if possible, but at least very good light. Relative humidity of at least 30 percent is desirable; preferred temperatures are 70 at night and 80 during the day. Keep the soil moist but don't let the pot stand in water. In two years it may be ready to bloom and bear fruit. Q. Our Concord grapes don't ripen properly. Only a few on a bunch get ripe at a time. If the ripe ones are picked, the others don't ripen. What could cause this? A. Plant physiologists believe it may be due to the vine being allowed to bear too heavily. This can cause uneven ripening, low sugar content and poor flavor. Delay picking the fruit until most of the berries are fully ripe. Q. Is sawdust O.K. to use to mulch my roses for the winter? Will it make the soil too acid? A. Sawdust is an excellent material for mulching roses. Contrary to popular belief, it doesn't make the soil acid. A nitrogen deficiency may develop if a lot of the sawdust is mixed with the soil. Q. Last year my Japanese holly was loaded with berries and this year there are none. Why? It appears to be healthy. A. Many plants skip a year when they have a heavy crop of berries one year. They need to rest up (store energy) before bearing again. Q. I brought potted geraniums in to my windowstill and they have stopped blooming. How can I start them up again? A. They will grow and bloom with only five or six hours of sunlight daily but it must be almost every day. When the days get longer in February and March they should bloom nicely.