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We have tried in vain to root slips of our rose geranium in water. The stems keep rotting off at the bottom. Is there something we could add to the water to prevent this from happening? Try adding a piece of charcoal the size of a marble per pint of water. Use real charcoal, not briquettes, as the briquettes are toxic to plants. If you still get no results, use moist perlite. Keep cuttings out of the direct sun.

We don't know if this is in your department, but we know birds are important to gardeners, so perhaps you can help. A male cardinal keeps flying to our windowsill and pecking at the pane. We note a female at our feeder in early morning and think there's a nest nearby. Why the strange behavior of the male? Male cardinals are very territorial (as are some males of other species). When they see their reflection in the window, they think it is another male and try to drive it away.

Since the male should be helping the female feed the young, it would be a good idea to hang long strips of white cloth from the tops of the windows so they flutter in the breeze, or else put paper doilies at intervals on your windows to divert the cardinal's attention.

Birds are important! A brown thrasher is known to eat more than 6,000 insects in a day - and a cardinal is of similar size. Think how many are consumed by babies when both parents are diligently keeping them fed.

We welcome suggestions for keeping birds away from windows.

We have found some strange-looking growths on the tip ends of the branches of our blue spruce tree. At first we thought they were cones, but on closer look, they are obviously part of the twig end and look something like a miniature pineapple. What should we do about them? Your tree has spruce gall aphids (common to all spruces), which have been working at the tips of branches. Each gall has several chambers with many nymphs (younger aphids) in each. Galls open in midsummer and the aphids continue their cycle, so try to cut them off and destroy them before the aphids emerge.

In the spring new growth can be sprayed with malathion (one of our least-toxic chemical sprays), and a spray can be added in late summer as well. A ''summer oil spray'' is also available that is nontoxic. Ask for it by this name.

In a conservatory we saw some begonias labeled ''Rex Hybrids,'' with handsomely colored leaves. We have tried to find them in florist shops, but to no avail. Could you give us a source? They are not often found in florist shops, unless the shop specializes in these plants. You could buy seeds and start your own, of course.

It will take several months to get plants the size of the ones you saw, but you will get many plants for the price you would pay for one full-grown one. Park Seed Company (Greenwood, S.C. 29647) has a good selection of begonias and will send directions for starting them.

Summer is a good time to start begonias, since the germinating temperature can be kept constant and homes are not as dry as in the wintertime, when the heat is on. Colors are truly outstanding when they are fully grown.

Wanting to serve fresh beans at dinner time, I picked them right after a gentle rainstorm. The next day, the vines were all wilted. My husband says he heard that beans should never be picked when vines are wet. Is there something to this precaution? Yes, he is correct. Anthracnose causes the wilting and, for some reason, disturbing the vines when they are wet makes them more susceptible to this problem.

It is also advisable not to water your bean plants during the day when the sun is shining on them. It usually causes burned patches on the leaves, and sometimes they wilt completely. It's far better to water any garden or lawn in early morning or early evening. More than 30 percent of the water can be wasted due to evaporation during the heat of the day.

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