Q: I inherited a bonsai ginkgo last summer and so far it has done well on my windowsill. I've been told that it should go outside for the winter. Could this be true?

A: Most trees and shrubs in temperate and frigid climates become dormant as days become shorter in the fall. Before they can break dormancy, they must experience low temperatures (40 to 45 degrees) for 1,000 to 1,500 hours. It is called their chill requirement.

Inasmuch as your bonsai has been indoors it probably is not hardened for winter and would be killed if taken outdoors. If you have a room where temperatures stay between 40 and 45 degrees, however, that is the place for it, for about 10 weeks.

Q: The roots of my silver maple are above ground, as are the roots of my neighbor's Chinese elm.Can I remove the roots without jeopardizing the roots without jeopardizing the tree?

A: It is risky to cut off the large roots of a tree. A lot of the small ones can be removed without risk. The large roots support the tree. If too manymany are cut, a heavy wind may blow the tree over.

It cannot be assumed that in addition to the large roots near the surface there may be other big ones down below in the soil. Oaks usually have a root system a foot or more below the soil surface, but not silver maples.

Q: Is it true that sweet potatoes should be handled like bananas?

A: Both are tropical and thereby subject to chilling injury when exposed to temperatures lower than 55 degrees. Bananas turn black, sweet potatoes develop hardcore upon cooking. Just like bananas, do not store sweet potatoes in the refrigerator.

Q: Is there an easy way to start a new grapevine from the old one I now have?

A: Layering is an easy way to start a new grapevine. In early spring dig a narrow trench about a foot long and three inches deep. Bend a good cane (branch) of last year's growth, and pin it in the trench. Make a shallow cut in the cane opposite each bud to speed rooting. When leaves start to open on the grapevine, cover the cane with soil. The following spring the rooted plant can be cut loose and planted in its permanent location.

Q: Our Christmas cactus is a nice healthy plant but it has never bloomed for us. We must be doing something wrong, what do you think it could be?

A: Like the poinsettia, Christmas cactus needs a long night of uninterrupted darkness in order to initiate flower buds.Under ordinary household conditions, the plants are in full bloom for Christmas if they receive no light from sundown to sunrise, starting about Oct. 1.

In other words, keep the plant in a room where it will get no light from sundown to sunrise. If you can't do that, keep it covered with dark cloth so that if the light is turned on even for a minute or two, it will not affect the plant.

Q: The mistletoe that is used for Christmas decoration, where is it grown?

A: Mistletoe actually is considered a weed. It grows (mostly) on woody plants rather than in soil. It is a parasitic plant that extracts water and nutrients from the tree to which it is attached.

The common mistletoe of the eastern United States is Phoradendron flavescens. There are other kinds in the West but none can be cultivated.

The mistletoe of history and legend is Viscum album, an Old World parasite. It was credited with mystic and medicinal power and was prominent in medicine and pharmacology until the middle of the 19th century.

Mistletoes are relished as food by livestock and deer. California Indians placed branches of the plant in strategic places to lure deer for shooting. Indian women in the Southwest drank a tea made of juniper twigs, often bearing mistletoe to promote muscular relaxation prior to childbirth.

Kissing under the mistletoe is a very popular activity at Christmas time.

Mistletoes are spread chiefly by birds that eat the seeds and later void them. Passage of seeds through birds improves germination of some species and never appears to harm them.

Q: My philodendrons on the windowsill refuse to grow upright, and instead appear to bend as if to better see what is going on out in the street. What could be wrong with them?

A: When a house plant is near a window, the stem of the plant bends toward the light. This is not because the plant seeks better light but because the cells on the darker side of the stem grow more than those on the lighter side.

This bending is always in the area of cell growth, which is a short distance from the tip of the stem. It is due to a growth hormone that increases in concentration more on the dark side than n the light side.

A stem which bends toward the light and is left in that position a few days usually does not bend back at the same point when the plant is turned around because the cells in the bent region have become mature.

If a plant is turned around half-way each day, the stem usually grows straight. If left in one position for a week or longer and then turned around, it usually grows crooked.

Q: Why can't I grow mums as large as those sold by florists?

A: In growing mums, removal of all but one flower bud per stem is necessary for the large, high-quality single bloom to develop. The small buds should be rubbed off or cut off close to the stem when they are no larger than a small pea.

The disbudding must be done every week until the flowers are produced. The plant will continue to produce leaf bud growth which should not be disturbed.