Q The buds on my Christmas cactus fall off before opening. What causes this problem and how do I remedy it?

A The masses of orchidlike flowers that Christmas cacti (Schlumbergera sp.) produce during the holidays make them popular houseplants. The cactus is easy to grow under the right conditions, but its buds often fall off before they bloom.

Exposure to heat or cold is a major culprit: If the plant sits near a radiator or in the path of a drafty window, it will almost certainly drop its buds. In cold areas of the country, damage may also occur between the store and your home as the plant moves through a broad range of temperatures in a short period. (Make sure the salesperson wraps the cactus in paper and places it in a bag. Then take it home right away.)

Watering too much or too little also causes bud drop, as does fertilizing the plant as it buds and flowers. Finally, gas from ripening fruit can knock off the buds of many plants, not just Christmas cacti, so don't keep them in the kitchen or anywhere produce is displayed.

For the best results, place the plant in a cool (64 to 68 degrees), draft-free location, with evenly moist soil and bright, indirect light; it should hold onto its buds, which will unfurl on schedule. Once the blooms fade, you can move the plant to a warmer location.

Distributed by the New York Times Syndicate. For more information on the topics covered in the Ask Martha column, visit www.marthastewart.com.