Dear Roger:  I've started growing cacti and I know you grow lots of them. How about some advice on the best cacti to grow indoors, not just the usual Thanksgiving and Christmas types? — Boyd, Fayetteville

Dear Boyd: I don't grow many cacti these days. They need good light and cool temperatures in the winter when they must receive no artificial light at night if they are to bloom the next spring. 

But just the other day I noticed a gymnocalycium in Roses for 97 cents and bought it. If the little gymnocalycium is kept outdoors and grown well this summer and kept cool and a little dry in the greenhouse, then next spring I'll be able to tell which species of gymnocalycium it is. Some species have white flowers. Others are purple, pink or pink and white. All of them bloom easily when they are small plants. And each flower can be larger than the cactus producing it. 

The real joy of cacti is their blooms.

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They'll grow fine in a south-facing windowsill. But if the room is not kept in the 50s at night in winter they won't bloom. And if the lights aren't turned off as soon as it's dark outside and left off until sunrise, they won't bloom. My heating system heats the house evenly throughout so I can't make my cacti bloom indoors. 

No sight has ever been more thrilling to me than the first time I bloomed a Rebutia minuscula. The plant, smaller than a thimble, was surrounded by glowing, silky, brilliant red blossoms larger than quarters. 

The rebutias and gymnocalycia come from South America. Most all the South American cacti have larger flowers, for the size of the plant, and are easier to bring into bloom than the ones that grow in the American Southwest. 

Others from South America that are special are the pariodias, lobivias (which take their name from Bolivia) and notocacti. All are readily available. You can find them in cactus collections from time to time in local garden centers and even in stores like Sears or Roses. Often they are grafted onto sections of cereus cactus stems. Cereus is the large-flowered cactus that blooms at night with fragrant white flowers. 

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The problem for most people is recognizing which cacti are which. Books about cacti, showing pictures for identification, can be ordered from book stores. They add much to the pleasure of growing the plants. There are also thousands of pages of information on cacti on the internet.

All the Southwestern American cacti are worth growing, even if they don't bloom for a dozen years or so. Their forms are interesting and varied. And many, such as the mammalarias, do bloom heavily when they're young and small. 

The Central American cacti are the most commonly grown of all. They include the Thanksgiving, Christmas and Easter cacti, all true cacti, and the orchid cacti, their larger, showier relatives that bloom from late spring through summer, depending on species, with flowers as big as small salad bowls. 

Breeding cacti is great fun. Without breeding, we wouldn't have the many colors we have in our Thanksgiving and Christmas cacti. The fine hybrids of cereus and nopaloxia wouldn't exist. There'd be very few orchid cacti — there are some businesses that sell nothing but orchid cacti, called epiphillum hybrids, in vast variety of leaf forms, sizes and flower colors from white through pink and red to purple. 

When I was in my 20s, I grew more than 2,000 species and cultivars of cacti in a large greenhouse for several years. 

I bred Notocactus hazelbergii  with several close relatives and produced kinds with larger flowers, more interesting spines and brighter flower colors than nature has produced. The Virginian-Pilot newspaper in Norfolk even ran a photograph of one of my cactus hybrids on its front page. 

I found that breeding cacti was quite worthwhile. 

If you have a greenhouse or a room that stays cool in winter, you should not be without cacti. They are among the most exciting plants that can be grown. 

I remember the first spring after I began to collect cacti. I had only about 300 then. But seeing most of them bloom for the first time was one of the most exciting events of my life.

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Send your questions and comments to Roger at orders@mercergarden.com or call 910-424-4756.  You may message photos and text to that number. Send pest or plant samples to Roger at 6215 Maude St., Fayetteville, N.C. 28306.