Ask the gardeners

We now have quantities of wood ashes. Are they of any value on our garden?

Indeed they are. They are dandy for sprinkling around plants to discourage cutworms, slugs, and snails, for example.

Used in moderate amounts, lime (one of the ingredients) can unlock the nutrients in the soil so the plants can more easily take them up. Wood ashes contain about 1 percent phosphorus, 25 percent calcium, and 5 to 10 percent potash.

Avoid using wood ashes on acid-loving plants, however.

If you've used ashes on the soil for two or three years, test the soil to make sure it isn't too ''sweet.'' Wood ashes can be sprinkled on the compost pile almost any time of year to help the materials break down.

Don't use wood ashes with fresh manure (rotted is fine) because it releases the ammonia. Last year we bought yellow corn and white corn at a fruit stand. The white kind was better than the yellow and yet we were always told that white corn was flat and tasteless. Can it be grown in the home garden?

Indeed! You have to go some to beat the delicious sweetness of certain white corn such as Silver Queen, a late corn (94 days). Ears are large and well filled with glossy white kernels. Unlike other corn the ears will hold on the stalk for 10 days or so without sacrificing quality.

Quicksilver is another white corn, earlier than Silver Queen and a close second in quality. It matures in 75 days. We just trimmed our grape vines and now find the ends of the canes are bleeding clear sap. Is this harmful?

No, it's natural for the canes to bleed some sap. You often see this after a limb of a maple, elm, or other ornamental tree is cut off. The sap flow will stop without any harm to the tree or grape vines.

(Reminder: Scores of readers already have asked for the free guide: ''How to Grow African Violets for Year-Round Beauty,'' offered in the Ask the Gardeners column Feb. 26. However, some of them failed to enclose a stamped, self-addressed envelope with their request. With postage at 20 cents these days, please don't forget the stamped envelope.)m

We have trouble telling when a house plant needs watering. How accurate are the moisture meters for house plants?

Most moisture meters can be a useful guide for anyone who has trouble telling if a plant needs watering. Most people can tell if a plant is dry or not by using their fingers. Even so, this is not always possible since the lower part of the soil ball can have ample moisture while the top is dry.

That's how many people ruin a schefflera. In other words, they pour water on the plant when the surface appears dry.

A moisture meter probed into the soil ball could prevent this. Some plant growers also get a reading by inserting a lollipop stick into the soil ball.

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