Q Last summer I grew cauliflower for the first time -- both purple headed and the white type. However, the white variety turned out slightly tan looking, not pure white like those found in food stores. To get white ``curd'' (heads) you must either grow a self-blanching type, which has leaves that curve up around the head to shut out sunlight, or you must pull the leaves up around the heads and tie them (or use a clothespin). This is done when the developing head begins to push against the leaves. This process of keeping out the sun is called blanching -- not to be confused with immersing a vegetable in boiling water for a short time, in preparation for packaging and freezing. Q My father, who was a master gardener, always made sure he was getting sphagnum peat moss, remarking that just any old peat moss was not good enough. Now that I've become a gardener myself I'm curious as to why he considered the sphagnum type the best.

Just plain peat moss is composed of the organic remains of a variety of plants which grew, then decayed, layer upon layer, until a bog was formed. It may take 100 to 500 years to produce a foot layer of residue, depending on the conditions under which the layers were formed.

Sphagnum peat moss is formed from layers of sphagnum moss. It is usually lighter brown, slightly more acid, lighter weight, and able to absorb more water than other peat mosses, which may have sedges or other types of mosses in their composition. Sphagnum moss, from areas where it was not yet decomposed into peat moss, was considered so ``sterile'' that it was used for bandages during the Civil War. Q Recently I have read several references to oil sprays as pesticides, for trees and shrubs, but the information is confusing. Some mention dormant oil and some refer to summer oil. A thorough explanation would be helpful, since I am a new gardener, as many of your other readers may be also.

Previously gardeners had a choice of using horticultural oil sprays for dormant trees and shrubs only; in other words, before buds started to open. Now horticultural oil sprays are made with a new formulation and, if diluted, can be used in summer as well as when growth is dormant. Entomologists at the University of Maryland have done extensive work with horticultural oil sprays and testify to their benefits. They emphasize it is important to read the directions and follow them explicitly. There are certain trees and shrubs that will not tolerate oil sprays, and some of these are listed on the container. However, if in doubt, try some of the spray on a few leaves and wait seven days to see if there is any injury before applying all over. Horticultural oil sprays are relatively harmless to beneficial insects and wildlife, and they are extremely effective against spider mites, aphids, mealy bugs, and scale insects.

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 horticulturalists.

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