Q Is it possible to grow mistletoe in a greenhouse? I know it must have a host plant, since it is a parasite, and is not hardy enough to grow outdoors in Minnesota. Would it grow on Norfolk Island pine or a large ficus?
Perhaps our readers can help with this, because we've never tried it. We have been told, however, that seedlings grow only on the same species on which the mother plant grew.
Seeds are sticky and are usually transmitted by the birds. The seeds stick to the bark, where they germinate and send haustoria (rootlike structures) into the tree's tissue. This is where mistletoe gets its nourishment.
The eastern American species grows primarily on linden, poplar, maple, and locust. Western species appear to be a problem on certain evergreens.
Q We received a lovely cyclamen and would like some tips for its care. We were told the soil must not dry out, so we have water in the saucer all the time. Now we notice that some of the leaves are turning yellow.
The soil should be kept moist but not soggy, or oxygen will be shut off from the roots and the leaves will indeed turn yellow. Water should not remain in the saucer.
Put the plant in a cool place at night (50 to 55 degrees F.), if possible. Give it bright light during the day, but it doesn't need the direct sun. Remove any spent flowers by grasping the stem and giving it a quick jerk.
If the plant should get too dry, it will flop. You can bring it back by setting it in a pan of warm water (even with the rim of the pot) and moving it to a cool place. Unless it has been dry for a long time, it will spring back good as new.
Q Our poinsettia has started to lose its leaves. The leaves first yellowed, then curled and dropped off. The plant was beautiful when it came from the florist.
Soggy soil will cause a poinsettia to lose its leaves, and so will dry air, especially if the plant is sitting near a radiator. Heat from fireplaces and wood stoves is especially dry and tough on all indoor plants.
Poinsettias do well if kept just moist, given half a day of sunlight each day , and kept at a temperature of 60 to 72 degrees F.
Move the plants away from windows on frigid, windy nights, because cold drafts will cause the leaves to drop.
We will send a bulletin, entitled ''How to Grow Poinsettias, Gardenias, and Camellias,'' to anyone who sends a self-addressed, stamped envelope to us. The pamphlet tells how to carry your poinsettia over for another year, as well as how to propagate new ones.
Q We have an African violet now sitting on a shelf under a small, blooming begonia plant. Awhile ago we noticed tiny plants growing in with the African violet, which now have turned into similar everblooming begonias. Will they harm the violet? We would like to save both of the plants.
Begonia semperflorensm (fibrous-rooted begonias) do not have large root systems, and eventually the plants will crowd one another. It is a good idea to use a pointed pencil to try to lift the begonia seedlings out of the pot.
Push the pencil into the soil slantwise about an inch from the plant and then pry up. If the begonia seedlings do not lift up easily, you should tip the pot upside down, holding the soil ball firmly with your fingers and with your thumbs on the rim of pot. Tap pot rim on edge of shelf.
Lay the soil ball on its side and gently pull the begonia plants away, then pot them separately. Repot the violet, adding a little more soil on the top where the begonias were removed.
Q I recently planted several dwarf apple trees. I was informed that the ''knob,'' located about 6 inches above the roots, is the place where the particular variety is grafted onto the dwarf rootstock. I was careful to leave the graft three or four inches above the soil, but now I am told that I should have set the tree deeper so the graft is even with the soil level. Why is this?
You have done it correctly. In the case of dwarf trees, the graft, or bud union, should be a few inches above the soil; otherwise you may lose the dwarfing effect if the scion (top part) roots and takes over. The tree is dwarf only because of the rootstock.
The bud that forms the top was taken from a standard tree and slipped into a T-shaped cut in the bark. If you are planting a standard-height tree, then the bud union can be at ground level or slightly below.
To make sure of varietal trueness, buds are taken from named standard trees and budded onto ''wild'' seedlings (nurserymen get seeds from fruit processors). Starting trees from cuttings is impractical, and seedlings without ''budding'' do not come true to the parent tree.
If you have a question about your garden, inside or out, send it to the garden 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 more than 25 years.m