IN THE GARDEN FOR FRUIT TREES, AMMONIUM SULFATE DOES THE TRICK.

Byline: JOSHUA SISKIN

In response to last week's column, which included a discussion of peach trees, I received an e-mail from Amarbir Gill asking: ``Should plum, apple, cherry and apricot trees be fertilized the same as peaches?'' and ``How do I keep ants off of my fruit trees?''

Fertilization of all the fruit trees you mention follows the same basic rules: Make sure you fertilize in September, and make sure you apply the correct amount of nitrogen fertilizer. The University of California recommends the use of ammonium sulfate for fertilization of fruit trees. This is an inexpensive product and it should be applied either once a year, in the early fall, or divided equally into two applications, one in fall and one in late winter.

A total of 4.5 pounds of ammonium sulfate per year should be applied to any mature tree, 6 years or older, of the types in your orchard. The perfect measuring device for this procedure is a frozen orange juice can, which holds 1/2 pound of ammonium sulfate when full. Thus, nine orange juice cans will contain 4.5 pounds of ammonium sulfate.

If you want to use manure, you better live near a rabbit farm, a barn or a stable, because you will need 32 pounds of rabbit manure and 63 pounds of cow or horse manure to equal the amount of nitrogen contained in 4.5 pounds of ammonium sulfate.

As to your other question, you may be relieved to learn that ants themselves do not damage fruit trees. The problem is that they bring with them several types of sucking insects that do cause problems. An ant will happily carry an insect pest (or its egg) into your favorite fruit tree. What's in it for the ant? Ants are fond of sap-sucking insect pests - aphids, mealybugs, scales and whiteflies - because of the partially digested sap, euphemistically called ``honeydew,'' these pests secrete.

To keep ants out of your fruit trees, wrap old nylon stockings around the trunks of your trees and slather a product such as Tanglefoot (available at nurseries) on the stocking. Tanglefoot is a sticky paste that literally stops ants dead in their tracks. You will need to check your stockings from time to time; sometimes a bridge of dead ants forms over the stocking, allowing their surviving relatives access to your tree.

Q: We planted an avocado tree awhile back from a seedling. This year, for some time the fruit has been dropping off. At least 12 dozen or more avocados, not big enough to ripen, have dropped. Could you help explain this?

- Harriet Jones

Northridge

A: More than likely, your avocado tree is suffering from lack of water. Of all the fruit trees in the Valley, the avocado requires far more water than any of them. I suspect that this summer's relentless heat has caused the premature fruit drop on your tree. In very hot weather, avocado trees should be frequently soaked.

Q: I planted three butterfly bushes early last spring, all in the same location. Two bloomed beautifully. The third grew to twice the size of the others but never bloomed. Any ideas?

- Alan Pollack

Woodland Hills

A: You may have two different species, one that flowers the first year planted and one that requires more time before it becomes acclimated to your yard and blooms. Another possibility, if it is the same species as its flowering neighbors, is that it received more fertilizer and/or water than the other plants and therefore put on an excessive amount of vegetative (stem and leaf) growth at the expense of reproductive (flower) growth.

TIP OF THE WEEK: This is the right moment to take cuttings from your hydrangea bush for propagation. Remove 6-inch cuttings from shoots that did not flower this year. Detach the bottom leaves from the cuttings, and cut the remaining leaves in half. Dip cuttings in root hormone and insert into moist vermiculite or perlite. Tent cuttings with plastic and place in a bright, cool location. Your cuttings should root within three weeks.