Q. Does fertilizer mixed with water deteriorate over time? I have a large can from which I've been mixing 1 teaspoon to 2 quarts of water for a few years now. Sometimes it seems to work great. Then during the middle of the summer it didn't appear to boost the plants along at all. Admittedly, the temperature was above normal, but it doesn't seem as though that should make the fertilizer inactive. Do you agree?

Sharp rises in temperature affect the functions of plants so they may not be able to assimilate the plant food during this period. Plants that are particularly affected are those with no mulch to keep the roots moist and cool.

If fertilizer is kept in a tight container, it will not deteriorate under ordinary conditions.

Q. I bought some split-leaved philodendron seeds and followed directions on the packet with great success. The plants are now about 15 inches tall and the leaves 4 inches wide, but they have no slits. Was I sent the wrong seeds? Under the common name on the package is written, in parentheses: Monstera deliciosa.

While it is commonly called split-leaved philodendron, Monstera deliciosa is not truly a philodendron. Other names are ceriman and Mexican breadfruit, the latter because of its large fruit, which is eaten in its native habitat, Mexico and Central America.

At first, the leaves are solid and begin to split after they are 6 or 7 inches long. The plant will grow in subdued light, but if the light is not bright enough, the leaves will remain solid.

The plant should not get full sun, however, since the leaves tend to get yellowish if overexposed. Nature has put splits in the leaves so they can withstand tropical downpours without being shredded.

Q. A neighbor's dog has chewed the bark off the trunk of one of our dwarf apple trees. The tree is about 21/2 inches in diameter and had just begun bearing fruit this year. There is a little bark at the base, but the bare portion extends to a few inches below the crotch. Can we save the tree by wrapping it in burlap?

If the tree had a continuous strip of bark, equal to one-quarter of the diameter of the trunk and running up and down so the sap could flow, it could be left as is. Since no bark remains, however, and the wound completely girdles the tree, it has no means of getting nutrients from the roots.

The one remedy, bridge grafting, can be done only in the spring when the tree's sap is beginning to flow.

Dormant scions (twigs) from any apple tree can be used to bridge the gap by implanting the ends in the remaining bark on both the top and bottom. This allows the fluid to bypass the wound in the trunk. A bridge graft would not be viable in the fall.

If anyone is interested in getting information on various types of grafting, most state colleges have bulletins on the subject. Our ''Green Thumb Book of Fruit and Vegetable Gardening'' has an illustrated section on budding and grafting.

Q. Before our potato tops browned, we noticed clusters of green balls on several plants. We have grown potatoes in our garden for the past three years, but have never seen these before. What are they?

Weather conditions were just right for the potato blossoms to be pollinated and form seed pods.

Often people ask us if they have a ''topato,'' meaning a cross between a tomato and a potato. Explorer potato seeds, offered in seed catalogs for the last year or so have come from similar structures.

Q. We were driving down a country road last summer with the limbs of large spreading trees hanging overhead. Then, as we moved into a clearing, we saw that our windshield was covered with a saplike material. It was hard to clean off, even with wiper fluid. Could it be that the sap was running out of the trees at this time of year? We noticed some flecks of cottony-looking stuff on our car as well.

You drove under trees that were infested with woolly aphids. There are several species, each having a preferred host. As they suck the juice from the leaves, a honeydew material is exuded which forms a sticky mess over anything it falls on. The leaves usually become cupped, protecting the aphids.

People who have this problem in the summer can spray with Malathion or the hot pepper-detergent spray made of 1 tablespoon each of hot pepper sauce and liquid dishwashing detergent in a gallon of water, plus one cup of rubbing alcohol.

Q. For some time I've wanted to ask if African violets really came from Africa. I know that plants are often misnamed. I was once told the Arabian violet is really a plant brought from the island of Socotra and is neither Arabian nor a violet.

You're absolutely right about the Arabian violet, or exacum. Socotra is an island in the Indian Ocean and the plant is really a gentian.

African violets, however, did indeed come from Africa originally.

In the 1880s Emperor Wilhelm II of Germany sent Walter von St. Paul-Illaire to be the youthful governor of German East Africa. His interest in the flora of the area led him to the discovery of the parents of our modern African violets. Samples sent to the Royal Botanical Garden in Germany were adjudged to be a plant previously unidentified.

The discoverer and his father were honored by the Royal Botanical Garden director when the plant was named Saintpaulia.

If you have a question about your garden, send it to the garden page, The Christian Science Monitor, One Norway Street, Boston, Mass. 02115. Doc and Katy Abraham are nationally known horticulturists.

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