ASK THE GARDENERS. Questions & Answers.

Q An evergreen ivy has taken over as a ground cover on a large shady area of my lawn (sample enclosed). It has now begun to climb the trunks of mature white oak and beech trees. Will this injure the trees? Is it an indication of bad health of the trees? J.H.C. Woodcliff Lake, N.J. The vine is English ivy (Hedera Helix), a good groundcover or climbing vine for walls, fences, etc. The rootlets will not harm trees because the plant is not parasitic. Since it likes shade, it does not cover the outer branches nor the foliage, shutting off the sunlight, as do some other vines. It is not an indication that your trees are in poor health, although the vine may grow on unhealthy trees as well as healthy ones. Hedera helix baltica (Baltic ivy) is a hardier form of English ivy for folks who live in colder regions. Q I read somewhere that windbreaks can save as much as 25 percent on fuel bills during the winter. I assume this refers to an evergreen planting placed on the side of the prevailing winds. Is there one type of evergreen better than another? How far from the house should they be placed? W.C. Oshkosh, Wis.

State colleges have found that well-placed windbreaks can save up to 34 percent on heating bills. The addition of properly placed foundation plantings close to the house can save even more. A landscape planner or well-informed local nurseryman can be of invaluable help in the selection of trees and shrubs and their proper placement.

Foundation shrubs (those around the foundation) hold a layer of insulating air close to the building. In your area some trees you could use are blue spruce, Norway spruce, Red and Austrian pine, hemlock and arborvitae. These have branches close to the ground but have spaces for air to pass through, reducing severe downdrafts.

You can mix the species and if you have room, two staggered rows are better than one. Do not forget that shade trees cut down on summer heat. An added bonus - all of these trees provide homes for birds. Birds are our best ``pesticide''! Placement depends upon your terrain and the location of your buildings on the site, so consult your nurseryman. Q Comment: This is in reference to your item on slugs, Nov. 28, 1986. For years we battled slugs and pill bugs. We dutifully cleaned up old mulch and disposed of it. In studying our nearby woods, we noted that nature does not remove old mulch, so we stopped removing it from our garden. Soil improved and so did plants. Slug population decreased.

Somewhere we had read slugs do not tolerate acid. The fact that our mulch consisted chiefly of oak leaves and pine ``straw'' made us wonder if the natural acid may have eradicated the slugs and pill bugs. For 15 years we have been free of these pests and we have used no poisons. We enjoy your articles and thought this might help someone else. Mr. and Mrs. W.A.C. Kilgore, Texas

We thank you for your comments. We would like to hear from others regarding possible repellent value of oak leaves and pine needles. We do know that we never find slugs in any of our fallen evergreen needles. This may be due to the resin and the terpenoids. We're not sure about the acid theory, since we find slugs are attracted to citrus skin insides and diluted apple cider vinegar.

Your observations are worthy of further study. We hope some college graduate student will choose slugs and snails for a project and take into account all the good information home gardeners have come up with. It may be the tanic acid in the oak leaves that repels these pests. Incidentally, it is terpenoids in orange skins which make them such a good flea control. To the garden editor:

I very much enjoyed your question and answer about rose geranium punch and it reminded me of the many edible treats my grandmother made from flowers. One which my brothers and I especially relished was made from nasturtium blossoms. They were layered on slices of homemade bread (spread with home-churned butter, of course!) and generously laced with homemade mayonnaise. The memory has prompted me to order nasturtium seeds. G.R. Temple, Texas

Doc and Katy Abraham are nationally known horticulturists.