Ask the gardeners

Our Santa Rosa Plum tree is about 8 years old. It bore a bountiful crop of huge plums but the fruit split before they were ripe. Then a green mold entered the split and the fruit rotted, unripened, on the tree. What caused this?

Your plums had growth cracks, a common occurence among cherries as well as plums. A dry spell, followed by rains, causes the fruit to expand so fast that cracks develop. Then fungi set in and cause the rot. There is no control except to keep the soil watered while fruit is developing.

We planted daylilies last year, which are blooming beautifully right now. Isn't it late in the season for this?

No. With the right selection, daylilies, or hemerocallis, will bloom from June to September. We have a light yellow one still blooming profusely (the last of August).

When looking at catalogs, select your varieties for all-season bloom. Some daylilies, like some irises, have the ability to rebloom later. (Refer to recent question on ''remontants'' regarding the iris.)

If you want more information about daylilies write to John Mason Algood, editor, The Daylily Journal, Route 4, Box 704, Waterboro, S.C. 29488.

I have a large grape ivy which had fairly large leaves. Now, even though it gets good indirect light, plus fertilizer, the leaves remain small. What can I do to get larger leaves?

We suggest you repot the plant, using a soil mix of 1 part each of garden loam, rotted manure or compost, and sphagnum peatmoss. Grape ivy likes a humusy soil. Also give it a liquid feeding about once a month to encourage lush growth.

When repotting, shift the plant to the next-size larger pot, not several sizes larger. Be sure to place gravel, crushed stone, pot shards, or small pieces of charcoal in the bottom of the pot for good drainage. (Do not use broken barbecue briquettes as they are toxic to plants.)

We just bought a home with an overgrown planting of shrubs around the front. Some are tall as the porch and others cover a part of the windows. Could you tell us how these could be pruned to get them back to nice-looking shrubs?

Shrubs used in a foundation planting, unless kept manicured two or three times a year, grow out of bounds. It sounds as though yours have grown neglected for some time.

In this case, tear them out and beautify your home with a new landscape job. It can increase the value by as much as 25 percent.

The outside of your home is just as important as the inside. Shrubs wear out just like drapes, rugs, and furniture. If you try to prune them back now, all you'll have is a bunch of bare sticks.

We were in the greenhouse of a large nursery recently and saw employees putting ''slips'' (cuttings) of evergreens in some white granular stuff. An irrigator kept the slips moist so they would root. Is it possible to do this in one's home? We do not have a greenhouse, but would like to root a few slips of our own.

Yes. The simplest way to root a few cuttings is to use perlite (what you saw in the nursery), sand, or sphagnum peatmoss as the rooting medium. Put some of medium in a plastic bag or a terrarium. Moisten it thoroughly so it is wet to the touch. Insert the cuttings about an inch or so, after you have pulled off bottom needles or leaves. Twist-tie the plastic bag shut, or put a cover on the terrarium. Cuttings should be 4 or 5 inches long. Keep them in good light, but not direct sunlight. If medium dries, add more water. Have patience, the cuttings will root eventually. Some types of evergreens root faster than others.

(Ed. note: Enclose a stamped, self-addressed, business-size envelope when requesting a phamphlet offered in this column.)

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. Doc and Katy Abraham are nationally known horticulturists, authors of several books on gardening, and greenhouse operators for 25 years.m