Tips on planting trees; clearing up confusion about oregano

Q When I retired, we moved to a new home with some area for shade trees. Please give some tips on planting so the trees will survive. I recall my father, who was a great gardener, saying that trees should be set in the ground at a slight angle, but I cannot recall the reason. Do you recommend this? Our soil is well drained.

We suggest you buy trees that are containerized or b&b (balled and burlapped) , rather than bare-root stock. If properly done, they suffer no transplanting shock.

Most important, dig the hole large enough to accommodate the root ball, with enough space on top to allow for a shallow saucer effect so needed water won't be diverted. This can be filled in with about an inch of coarse mulch (bark chips, etc.) to shade the roots and keep in the moisture. Pull the mulch away from the trunk an inch or so.

Before setting a tree into the ground, mix some humus with the subsoil and put a few inches of this mixture into the hole. Firm the soil around the ball as you plant, and water thoroughly when planted. In dry spells, water at least once or twice a week.

Your father's suggestion is a good one. Lean a tree slightly toward the prevailing direction of the wind. This helps the tree grow straighter as the wind pushes it the opposite way.

Q A year ago you gave me instructions for keeping my florist's azalea over. I followed your advice and, believe it or not, I have a beautiful plant with pink blooms. It isn't quite as full as last year, but enough to get plenty of ah's and oh's from friends. It has a few long shoots jutting out, and I'd like to know if these can be cut back.

You can cut the long shoots back a little now, then shape up the whole plant as soon as it finishes blooming. The fact that you put it outside in a shady spot during the summer and kept the peaty soil moist at all times brought it through the summer.

The cool night temperature (about 55 degrees F.) after you brought it back indoors in late fall induced it to set buds.

Q Last year I bought seeds of oregano from three seed racks put out by three separate companies. When the plants developed, they were all entirely different, including the flavor. One batch of plants closely resembled the marjoram I was growing, while another one was like the perennial oregano my grandparents brought from Cyprus many years ago and which was lost during last winter's unusual harshness. What do you say?

Many of us have had a similar experience. Even herbalists don't agree as to which species of the genus Origanum is the true oregano. Origanum vulgare is the one most commonly listed in seed catalogs and is often called ''wild marjoram.'' Sweet marjoram is also called oregano by some specialists and is listed as Marjorana hortensis. Still others claim that Origanum heratheoticum is the true oregano.

All the above are native to the Mediterranean area. We suspect the particular plant of each flavor was transplanted to America by the emigrants who relocated in a particular area. Other plants, such as Lippia Graveolens (Puerto Rican oregano) and Coleus amboinicus of the mint family (Cuban oregano) further complicate the picture.

Interestingly, Origanum is purported to be an ancient Greek word meaning ''delight of the mountains.''

Q Last summer the leaves on a branch of my 10-year-old rhododendron curled and turned brown. I sprayed the bush with benomyl, but it had no effect, as several more branches wilted completely. Is there something I can do to stop the problem? I cut off the wilted branches.

The symptoms indicate you have borers in your rhododendron. Removing the branches was a good idea. Be sure to get down into the live tissue where there are no borers. Inspect the remaining branches for holes and protruding sawdust material. After removing the borers, be sure to burn or seal them in a plastic bag for disposal.

Small black moths lay eggs in May and June on the twigs. As soon as the larvae hatch, they bore under the bark, causing the leaves to wilt and finally destroying the whole branch.

Benomyl is a fungicide and will not kill the moths or larvae. Spraying the bark with latex paint will repel the moths. Once the larvae are inside, they are difficult to control. Some gardeners try to push borer paste into the holes with the tip of a pencil. Success depends on thoroughness. Borer paste can be found at garden stores.

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, authors of several books on gardening, and greenhouse operators for more than 25 years.