Having been lucky enough to travel to Arizona in the past few years, I have seen the saguaro cactus in the flesh. Its tall, branching form silhouetted the arid landscape just as it has in so many westerns.
At the other end of the spectrum, I also saw the world's smallest cacti, Blossfeldia liliputana, in Kew this summer. This diminutive plant and the contrasting giant perfectly illustrate the diversity of cacti, and in this article I will only be able to give a taste of what they offer.
In a retail environment, the largest plants just cannot be represented. The biggest cacti you might find are the golden barrel' (Echinocactus grusonii) or fishhook barrel (Ferocactus wislizenii). Like all the cacti, bar one, these species come from the Americas. Most are found in regions that experience drought, but there are a few found in tropical forests such as Schlumbergera, known as the 'Christmas' cactus, which has flattened stems from which brightly coloured flowers emerge and is commonly grown as a houseplant.
Cacti are sometimes sold as a novelty item. A friend recently saw them on a market stall covered in glitter spray. They did not look like they would last very long. But for the serious collector, it is worth getting in touch with the British Cactus & Succulent Society, which gives detail on some of the more unusual species and where to source them. There is even a bright, colourful and simple section for kids interested in cacti. It might be worth linking plant sales with this resource because children are apparently keen buyers.
The diversity of form that this group provides is incredible. Their shape can be globular or columnar, or they may form chains of flat or cylindrical pads. They may be solitary specimens or form clusters, which can look very dramatic. The plants often develop ribs or tubercles.
The rainforest cacti are usually spineless and epiphytic, while desert cacti are usually covered in spines. Spines are highly modified leaves that emerge from furry areolas. They prevent water loss by reducing air flow close to the cactus and providing some shade, as well as being a collection point for morning dew and protection from hungry animals.
They are quite variable, being short or long, curved or straight and of different textures and colours. Many cacti will also produce beautiful flowers every year. The following genera are likely to be prolific flowerers at a young age: Rebutia, Sulcorebutia, Mammillaria, Gymnocalycium, Echinocereus, Notocactus, Parodia, Lobivia and many species of Echinopsis.
Cacti generally need to be grown under cover, apart from in the summer when they can stand outside. They need good light for successful growth, which is why the ideal place is a greenhouse, though many people do manage to keep them well by windows in the house. Generally they need a minimum temperature of about 5 degsC, though some can cope with lower, and they should be kept dry in the winter.
In spring, give them some shading and provide greater ventilation. Start watering late in March, when you should see growth start. Let the plants dry out between waterings and do not let them sit in water. Feed with a balanced fertiliser such as a tomato feed and water regularly until early October.
What the specialists say
- Linda Goodey, co-proprietor, Cactusland/Southfield Nurseries, Lincolnshire
"We believe that with a little care, cacti can be the most rewarding plant, with their range of shapes, forms, colours and beautiful flowers. In the summer, with the right varieties, you can have weeks of flowers, and in the winter a range of plants with beautiful structural forms to enjoy.
"There are hundreds of varieties that the public do not usually see.
As long as they are in a position to receive sunshine, they are one of the most tolerant house/conservatory plants. We like cacti that flower easily. We do a lot of hybridising and find it very satisfying creating new varieties.
"We have five main tips for successful growing. First, the plants must be kept in a sunny position - windowsills, conservatories, porches or greenhouses. Give them regular water in the summer months (April-October, about once a week). We suggest top watering as they do not like to stand in water for any length of time, and allow plants to dry between waterings.
"In winter, keep them dry as most cacti need to go dormant. And re-pot the plants when they have got too big, using a gritty compost. Cacti should also be fed with a specific cactus feed or a high-potash feed. Finally, they may need to be sprayed three-to-four times a year with a systemic insecticide as a preventive measure."
- John Pilbeam, owner, Connoisseurs' Cacti, Kent
"Cacti are one of the most interesting, diverse families of plants on the planet because of how they are incredibly adapted to survive. The key to their popularity is the variety of form, both of body and spination, and their often incredibly beautiful, sumptuous and, to the uninitiated, surprising flowers.
"My favourite are the smaller-growing, globular cacti, which are not demanding of too much space and often more easily grown to flowering size, such as Mammillaria, Rebutia, Sulcorebutia and Gymnocalycium to name but four.
"The main requirements are good exposure to sunshine, watering and feeding during the growing season from about March to September, and complete dryness and protection from frost in the winter months from the end of October to the end of February. Glasshouses are the ideal location for growing, but conservatories or sunny windowsills will suffice.
"The main pests are mealy bug, characterised by white woolly patches containing the tiny woodlice-like bugs, and red spider mite, barely visible but betrayed by a brown coating on the skin of the plants and minute webbing between the spines. The latter can be seen with a magnifying glass."
- John Winterson, deputy plant buyer, RHS Plant Centres
"Most of the cacti we sell are in mixed collections and small individual cacti - 5.5cm, 6.5cm and 8.5cm are the most popular sizes. These are followed closely by mixed Lithops and those grafted cacti with the coloured tops.
"The next best sellers are small planted cacti arrangements. These collections have each plant individually named by our specialist UK cacti grower, so they are identifiable for collectors. We find that children love to buy them, attracted by their small size, ease of care and affordability.
"One of my favourites and I think the prettiest of the cacti we sell is the Rhipsalis - there is a now a wide range of colours available, from whites through to salmons and reds. These are a traditional table houseplant for Christmas alongside poinsettias.
"Because the cacti vary so much in size and shape and range, our displays tend to be rather mixed, but we do add in a few specimens to give some height to the display. We add colour with a backdrop or brightly coloured pots to go with the plants. The plants are easy to maintain but can be hard to water if the dome of the cacti covers the top of the pot. They seldom get any pests or diseases but we do watch out for mealy bug."
Species and varieties
- Cleistocactus strausii 'Silver Torch' Award of Garden Merit (AGM) (H1) is an erect, columnar cactus whose stems branch and are densely covered with short white spines. Tubular rose-red flowers are borne along the stems in summer. Needs to be grown indoors. Height: 1.5m.
- Echinocactus grusonii, the golden barrel, originates in Mexico. In its native habitat, plants can grow to 90cm wide and form clusters. Cultivated in the UK, they usually grow well but will only reach up to 30cm across and are unlikely to flower. It features golden yellow spines in neat rows and ribs form as the barrel matures. Half-hardy.
- Ferocactus wislizenii, the fishhook barrel, comes from the south-west of the USA and northern Mexico. It is not hardy in the UK but some would risk it outside in a well-drained, south-facing site because it has the potential to be a large, impressive plant. In the Americas, it can reach up to 1m across and 1.5m high.
- Gymnocalycium baldianium is a small cactus, forming a grey/bluey-green ball, with knobbly ribs and bristle-like radial spines. In the summer, large red or dark-pink funnel-shaped flowers are produced. Grow under cover. Height and spread: 10cm.
- Mammillaria bombycina AGM (H1) forms clusters of cylindrical stems. Dense white hair gives it a distinctive appearance and white radial spines and longer brown spines emerge from its tubercles. Small deep-pink flowers are borne at the stem tip in the spring and summer. Height and spread: 50cm.
- Matucana weberbaueri are flattened, round cacti with smooth green skin covered with contrasting light-yellow/brown spines. This species also produces large tubular yellow flowers. Height: 30cm. Spread: 10cm.
- Parodia magnifica syn. Notocactus magnificus AGM (H1) has a glaucous body featuring white felted ribs and plenty of yellowy-brown bristles - and sulphur-yellow flowers after some years. It is native to Brazil and Uruguay where the land is dry and the daytime temperatures high, so it likes to be kept outside in the summer. It can cope with temperatures as low as 2 degsC.
- Rebutia muscula 'Little Mouse Crown' AGM (H1) is a clustering cactus with spherical stems, bearing bristly spines and showy, bright reddish-orange flowers in summer. Height and spread: 10cm.
- Rhipsalis baccifera 'Mistletoe' is so known because of its thin, fleshy stems and round, white fruits. It is an epiphytic cactus, the only one to be found growing naturally outside of the Americas, in tropical Africa and Sri Lanka. It was either introduced by migratory birds or on European ships trading between South America and Africa. Ideal for hanging baskets.
Thank you to Floramedia, which supplied the images for this article from its photo library