Dear Carol: I have a large sawtooth blade cactus. How do I keep the ends of the leaves from turning brown and shriveling up?
Dear Carol: Please ignore my last e-mail. After seeing the photo accompanying last week's column, I realize that what I have is not a cactus but an Aloe vera. -- N.C., Camillus.
Dear N.C.: People have trouble telling what's a cactus and what's not. All the cacti belong to one plant family, the Cactaceae. Plants in this family have certain characteristics that botanists use to group them together. They don't all grow in the desert, and they don't all have spines. Most cacti are native to the Americas, from Alaska to South America almost to Antarctica. Cacti have no leaves or only vestigial ones. The green stems, called joints, do the photosynthesis. All cacti flower and produce fruit. The flowers last only a short time but can be spectacular.
Many cacti are adapted to survive in dry places. Plants can survive drought by storing water in thickened stems and leaves. These types of plants are called succulents, from the Latin word sucus, which translates as "juice." Many plant families have members that are succulent, African violets, impatiens and bedding geraniums included.
Aloe vera is a succulent, but not a cactus. If a plant grows in a rosette or a fan, it is not likely to be a cactus but a member of another plant family. Aloes are in the family Asphodelaceae.
Plants have to maintain the water in their cells to function normally. They balance the amount of water by pulling it up from the soil through their roots and by losing it through openings in their leaves. When the leaf tips turn brown, either too much water is being lost or not enough water is being pulled up. The tips are affected first because they are the farthest from the roots and are supplied last.
The possible causes are air that is too dry, soil that is too dry or an inadequate root system. The root system may be too small, especially in a container. The roots of succulents normally spread widely. The root system may be damaged by too much water or by too much fertilizer.
Brown tips can be prevented, but they can't be cured. They can be trimmed off neatly. If a leaf is pointed, say on a spider plant, trim the leaf to a point rather than cutting it off straight across. It will look better.
Dehydration is just one of the perils that plants in arid places face. Another is being eaten by thirsty animals. The spines that many succulents have are a deterrent to animals. Euphorbias can be spiny as can be, like "crown of thorns" E. milii, but they are not cacti.
Carol T. Bradford, of Syracuse, has been gardening in Central New York for more than 25 years. Her column also appears in Stars magazine Sundays. Send questions in care of Home & Garden, The Post-Standard, P.O. Box 4915, Syracuse, NY 13221, by fax to 470-2111 or by e-mail to email@example.com. Letters might be edited for space and clarity.