Q. Earlier this fall we had a curious phenomenon on our pear trees. We had fruit as well as blooms, all at the same time. We're wondering what caused this to happen and if it will affect the fruiting next year.

Our mail indicates this off-season bloom was peculiar to certain areas that had many dark, rainy days after several weeks of dry, sunny weather. Also, the trees did not set fruit the preceding years because of poor pollinating weather.

When the latter happens, the trees accumulate a greater amount of carbohydrates than is used in current fruiting; as a result a second bloom may appear.

Also, the Agricultural Experiment Station of Cornell University tells us that fruit trees will respond to photo-periodism, as do certain flower plants such as chrysanthemums, which the shorter days of late summer and fall trigger into bloom.

Florists have learned how to regulate the flowering of mums and other plants that are responsive to photo-periodism by either shortening or lengthening their day, either by shading or using lights. Some fruit trees will produce blooms in the fall if nature has reduced the number of daylight hours in mid to late summer with unusually dark, cloudy weather. Fall bloom will not affect next year's crop.

Q Someone has given me a calla lily tuber, and although I have admired the blooms in florist shops, I have no idea how to care for it so I can get some blossoms. How do I pot it up and when should I expect it to flower?

Pot it up in a 5-inch pot using a mixture of 2 parts sphagnum peat moss (or rotted compost), 1 part sand or perlite, and 1 part garden loam. A tablespoon of bone meal or superphosphate mixed in the soil will help produce blooms.

Water the tuber thoroughly and set it in a dimly lit place at a 55- to 60 -degree F. temperature until it starts growth, then move it to a light place about 70 degrees F. and give it a feeding of liquid fertilizer.

As leaves and flower stalk grow, move the plant to a sunny window and keep the soil ''just moist.'' It will take the tuber 15 to 18 weeks to produce bloom. Feed once during blooming. In early June you can begin drying it off. Turn the pot on its side until September when you can repot and start all over again.

Q As a child I admired a lovely shrimp plant kept in almost perpetual bloom by an aunt. A year ago, when I moved back to my hometown, I became the owner of this lovely plant. But alas, it soon went out of bloom. Could you give me some pointers?

Shrimp plants (Belaperone guttata) are indigenous to the tropics, hence they need a temperature that does not fall much below 65 degrees F. If the temperature falls below 60 degrees F., they will stop blooming. Also, they like four or five hours of sun a day, and when in bloom, a feeding about every three weeks with a liquid plant food.

If they go out of bloom, do not feed until buds appear again. The soil should dry out slightly between waterings; but when watering, do it thoroughly. Your aunt probably pruned the plant to keep it bushy and after a couple of years rooted cuttings to grow into a new plant. Old plants usually get woody stemmed and if not pruned regularly become scraggly-looking. Even with diligent care they usually become overgrown, so it's best to start new plants from cuttings every two or three years.

If you have a question about your garden, send it to the garden page, The Christian Science Monitor, One Norway Street, Boston, Mass. 02115.

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