Q: I watered my African violets the same way I regularly do it and half an hour later they were badly wited. They stayed that way for several hours. What could possibly have caused it?

A: Probably the water was too cold. It is not unusual for a house plant to wilt after having been watered with cold water (40 to 50 degrees). The cold water seriously affects later absorption by the roots.

A common example is with cut flowers. If they are put into cold water after being cut they are likely to wilt badly.

That is why lukewarm water should be used to waterhouse plants and for cut flowers.

Q: My grandmother had a sweet shrub at the farm that was wonderful when it was in bloom. I picked the flower buds, wrapped them up in my handkerchief and took them to school.They stayed spicy fragrant all day long. I bought two of these shrubs four years ago, they bloom every year but the flowers have no fragrance. Is there anything I can do about it?

A: You probably bought a couple of lemons. The one that has fragrant flower is Calycanthus floridus, the Carolina allspice. However, many plants sold under this name by nurseries have little or no fragrance. Moreover, because of little demand for the shrub, many nurseries do not stock it now.

If you can find one at a nursery when it is in bloom, test the flowers by squeezing them, buy it if they are fragrant. The plant is easy to start from cuttings. But the cuttings must be from a plant that produces fragrant flowers.

Q: Now I have a greenhouse but I am new at it. Is it practical to try to grow some radishes in it?

A: Radishes are easy to grow. Try small globe varieties. Plan to sow them at two-week intervals so you will have fresh ones coming along all winter. Light sandy soil is preferable for smooth, tender radishes of uniform size. When they have produced their second set of leaves thin out plants so ther are only 9 or 10 left to a foot of row. They prefer cool temperatures (50 to 55) at night.

Q: I have tried several times to transplant a black walnut tree from a field to my front yard and each time they died. Is there some special treatment they require?

A: Black walnut trees are extremely difficult to transplant successfully because of long tap roots which they develop early in life.

Pick a very small one to transplant. Early spring is by far the best time. Dig the tree with at least 24 inches of taproot. Get it back into the ground as quickly as possible. After planting it, soak the soil around the roots thoroughly with water and keep the tree watered during dry weather for three or four years. Keep weeds from growing near the tree until it is well established.

Q: I shelled a lot of black walnuts in October and put them in the refrigerator in a plastic container to keep for Christmas. Now (in early December) they are not fit to eat. What could have happened?

A: In the shell the walnut kernel is covered by a pellicle (skinlike substance) which prevents oxygen penetration. When the pellicle is broken, the oil in the walnut absorbs oxygen and rancidity occurs.

Commercially shelled walnuts are protected by a pellicle substitute to prevent rancidity, according to Dr. Lois A. Simonds, Ohio State University specialist. However, this must be followed by correct storage at home.

Shelled walnuts should be stored in the refrigerator in a tightly covered container.

Q: When is the best time to divide rhubarb? Our plants are getting overcrowded.

A: Rhubarb usually needs to be divided when it is 4 or 5 years old. The best time is late fall or early spring when the plants are dormant. In California division is sometimes made in May after the crop has been harvested.

The crowns may be cut into as many pieces as there are buds. Under favorable conditions a piece of root with one strong bud will produce a good plant in one season. These grow into large vigorous plants that will provide some stalks for pulling the spring after planting.

When old crowns (6 to 10 years old) are divided, use only the vigorous outer portions for planting. Discard the center of th crown. Always leave as much root as possible with each piece of crown.

If you want to keep the rhubarb growing in its present location, division can be made by spading away parts of the crown. The part removed can be used for new plants.