For non-devotees, that would rule out quite a lot of cacti. Even Terry Hewitt, one of the most enthusiastic and knowledgeable cactus experts, hesitated as, touring his show glass-house, we came across a brown mass of shrivelled foliage. How, I asked him, could he tell whether it was still in the land of the living?
"With difficulty," he confessed. "It's an aliocarpus and it's supposed to look brown like that, but it does have a slight green tinge when it's alive. That one could be dead, but it's quite rare and valuable so I'll keep it for a while."
What, then, is the point of these often prickly and ungainly indoor plants? Their crude pet names are clues to their inherent lack of daintiness - Old Man Cactus, Living Granite, Rat's Tail, Elephant's Foot, Mother-in- law's Seat. Even their botanic names tend to indelicacy: one variety is called gasteria because it is like a stomach; another, with blunt honesty, is named horrida.
For Mr Hewitt, though, the merest hint of scepticism is hurtful. He explains the curious appeal of the cactus: "There's an ever-increasing demand because they're a very tolerant plant and easy to grow. Modern houses with central heating are death traps for most house plants. People can go away on holiday for six weeks and leave their cactus and it'll be perfectly happy."
Well, yes, but the same is true of aspidistras and garden gnomes. A more relevant question is whether they are aesthetically pleasing. We came to a prickly pear, its fleshy green leaves shaped like a tennis racket and adorned with purple fruit that clashed violently with the rust-coloured pimples at the base of the spikes. I suggested to Mr Hewitt that, although the purple was an attractive hue in isolation, the composition as whole was rather a mess.
"Different people like different things," he murmured philosophically. That thousands of people do like cacti is apparent from the numbers of customers who make their way to his 10,000 sq ft glasshouse in Ashington, West Sussex, to look at his plants. He estimates that there are at least 25,000 dedicated collectors in the country and he gets hundreds of overseas visitors as well.
The largest plants, chiefly the column cacti, admittedly have a statuesque appeal, redolent of the Arizona desert: some are taller than 8ft and you would need a large indoor space to accommodate them. Exec-utives anxious to make an impact on business visitors put them in their office lobbies - but out of reach if they want to avoid injury claims. Hewitt insists that there are also enthusiasts who keep them at home, sometimes designing a whole room around them.
More manageable are such subjects as the orchid cacti (epiphyllum), which hail from the jungle rather than the desert. There are 200,000 kinds, many with spectacular summer flowers. But the most popular cactus remains mammillaria zeilmanniana, the plain and prickly little knob seen on so many window sills.
The peculiarly lumpen shape of the standard cactus derives from its dry habitat and consequent need to conserve moisture. This it achieves by developing maximum bulk with minimum surface area. By contrast, those that originate in jungles need above all to catch whatever light is going, so they form elongated stems - aporocactus, or Rat's Tail, is an example.
The cactus is one of a larger group of species known as succulents, characterised by their ability to store moisture and thus survive drought. The distinguishing features of the cactus are its areolas, the small pads that the spikes or flowers spring from: no other species has them. Nearly all real cacti are native to the Americas. One of the many surprises for the non-expert is that not all of them have prickles.
Mr Hewitt also grows and sells non-cactus succulents, of which the lithops (stone flower) has a large following. These are small globular plants, hard to distinguish from the pebbles that surround them. Mr Hewitt explains that they do not consciously camouflage themselves but that natural selection ensures that plants that blend in with their background are less likely to be spotted and eaten by predators.
There is something primeval about cacti. Some of them were undoubtedly familiar to the dinosaurs 150 million years ago. Probably the original cactus, marking the point at which it diverged from other plant forms, is the pereskia, still popular today for its masses of highly scented creamy pink and orange flowers. The thorns and pads appear on its fleshy stems, like a weird form of rose.
A few varieties have medicinal properties. Testudinaria, which grows out of what looks like a carved wood-en lump, is the plant from which cortisone was extracted. It was nearly extinct in the wild before scientists discovered how to synthesise the drug. The idea of the contraceptive pill originated with dioscorea, whose prophylactic qualities were first discovered by fun-loving Mexicans.
Some cacti and succulents have eccentric habits. There is Queen of the Night, an epiphyllum with spectacular flowers a foot across that only last for a single night: I imagine true devotees reverse their sleeping pattern during the flowering season.
Then there is the agave, the succulent that looks like a giant pineapple top and flowers only once in its lifetime, when it is about 35 years old. It can grow enormous, up to 18ft in diameter, so disposal of the corpse can be a problem.
Mr Hewitt's current prize agave, some 5ft across, is 30 years old, so he is steeling himself for bereavement. When it does flower, it is touch and go whether he will be able to collect the seed from it since not all of them are self-fertile - and it is obviously rare for two to flower in the same year. This year he was lucky: an agave that flowered proved to be self-fertile and he was able to collect hundreds of seeds that are now germinating in his nursery glasshouse. He grows all his plants from his own seed, pollinating many by hand.
They take between three and five years to reach a saleable size and he calculates that he has some 750,000 plants in his nursery at any one time. Prices range from £1.25 for the smallest pots containing the most common specimens to several hundred pounds for a tall column cactus.
Mr Hewitt has been at the Holly Gate Nursery for 25 years. "It started as a hobby. I used to spend lots of time up here as a customer. Then I was taken on as manager and 12 years ago my wife and I bought it."
Cacti must be handled carefully. Some have thorns that expand once they enter the flesh, making a larger, more painful hole on the way out. Mr Hewitt insists he has never been wounded in the line of duty - except by non-believers making snide remarks about his treasures. 8
TERRY HEWITT'S CACTUS TIPS
The best compost is a mixture of peat and grit. Some people think they should grow cacti in sand, since they come from the desert - but in pots sand tends to clog. The plants should be kept almost completely dry in winter at a temperature of between 45-60F (8-18C). In summer they need a reasonable amount of water and a higher temperature to grow and flower, as well as plenty of light. Jungle natives such as the Christmas, Mistletoe and Orchid Cacti need to be moist all year and do not want full sunshine. All the plants need feeding at least once a month in summer, with a special cactus feed or a tomato fertiliser. They are quite easy to raise from seed provided they are started in warmth. Germination takes between three days and a month and some will flower in their first year.
The address of Terry Hewitt's place is: Holly Gate Nursery and Cactus Garden, Billingshurst Road (the B2133), Ashington, West Sussex RH20 3BA. Tel: 0903 892930. Open 9-5 every day except Christmas. Admission £1.50, pensioners and children £1. Terry Hewitt's Complete Book of Cacti and Succulents is published by Dorling Kindersley at £15.99.Reuse content