GARDENING : Growing Cacti Needn’t Be a Prickly Task

Many types of cacti will flourish and even flower indoors in a sunny, south-facing window.

But avoid large growers that require high amounts of light, such as saguaros, cereus or prickly pears. Better choices are such smaller types as mammillarias, golden barrels, pin cushions and echinopsis, which need good light but not high amounts of it.

Experts say amateurs will be most happy with those able to thrive in a container no larger than a 6 to 8 inches wide. The large growers may be available in tiny pots but soon become unattractive and gangly indoors.

Many of the smaller-growing cacti can be purchased in 2-inch pots for a few dollars. Move them to larger pots as they grow. They are pretty easy to care for and a lot of fun.

If a collection is for sale in a small container, that’s a good way to go. Designers of those arrangements usually have a nice eye. However, be prepared to transplant eventually.

The pot size is important. Don’t put a 2-inch cactus in a 6-inch pot. Put it in a 3-inch, or maybe a 4-inch, moving it along as it grows.

Flowers are possible within a year or so. Some plants may be sold in bloom. Flowers last only a few days. If plants flower periodically, your light conditions are correct.

After proper selection, the trick to growing cacti is watering and good drainage. Put a finger on the growing medium and if it feels moist, it’s wet enough. Water when it feels bone dry. But plants won’t look very healthy if they haven’t been watered properly. The root systems die.

When a plant starts to grow, throwing out new spines or stems, that’s the time to encourage it with water and fertilizer to initiate flowers.

During such growing periods, include an all-purpose fertilizer with every other watering, applying about an eighth to a quarter of the manufacturer’s recommended dosage. Slow-release fertilizers also work, but in small amounts.

For a growing medium, a good starting point is about half organic matter, 40% sand and 10% perlite, blended well.

Even if labeled cactus mix, pure-organic potting soils are very hard to wet up and very hard to dry out. They need amending with sharp, masonry sand and perlite.

After blending, test the mixture to make sure of drainage. A good method is to fill a pot within an inch of the top with the mix--without a plant; tamp the mix as usual and fill it with water. If water doesn’t come out of the drain hole within one or two minutes, add more sand and repeat the process until the mixture drains right.

Soil from your yard, as with any type of container plant, is almost certain to be nothing but a headache.

It’s a good precaution to treat each new cactus as a bare root plant, discarding the former growing medium. That ensures the drainage is identical for all your cacti, and if there are hidden insects, they are discarded with the old mix. Before transplanting, loosen the root ball slightly. To protect against thorns, wrap sections of a newspaper to hold the top.

Healthy plants are the best insurance against future pests and diseases.

To remove a cactus from the container it’s been growing in, carefully knock most of the soil from the roots so in effect it is a bare-root plant. Once the roots are exposed, set the cactus in a shady location for a few days to dry. This helps minimize chances of rotting.

The planting hole should be large enough so the roots can be spread to their full length. Soil is then filled to the same level the plant was in the pot.

There are different theories on where to place the plant--on a small mound, level or in a small depression that will catch water.

Generally, it depends on how you plan to water. If you never intend to water, a little depression is worthwhile. Botanical gardens usually plant flush to the surrounding surface, since this looks more natural.

Wait a few days to water after outdoor planting and then, for the first year, apply once a month in summer and none in winter. Consider, too, growing cacti in containers in a sheltered area of the patio.

It’s time to repot a cactus when it reaches half a inch or so from several sides of the pot. Sometimes a cactus is growing over the container sides in such fashion that it seems impossible to transplant it.

If it’s a Ming Dynasty vase, discard the cactus. Otherwise, break the pot.