How to Grow Cactus Indoors?

You either love cacti or hate them; there seem to be no two ways about it. Or you may be in the first stages of becoming fascinated by their bizarre shapes and their ability to sprout flowers from the most unlikely places. Cacti are the Martians of the plant world; they are the only plants which can survive living in extreme conditions of heat and drought. Because of this they have altered their way of life and form so completely that they no longer look or grow in the same way as conventional plants.

Many cacti have developed a plant body which is almost completely round; such a shape combines the least surface area – and therefore loses least moisture by transpiration – with the greatest internal area for retention of moisture. Cacti tissue has also developed so that it is capable of storing water for extremely long periods, even during great heat.

Many cacti are also exceedingly prickly or spinky, a development which protects them from grazing animals. Their roots are often very fine and close to the surface, but extremely wide-reaching, so that when rain does come they can absorb as much as possible for the short time it lasts; this root development is also essential in places where there are heavy dews. They flower mostly in May and June, but very briefly of the short time during which moisture is usually available.

Cacti are, with the exception of the Rhipsalis, natives of North and South America. Civilization has, however, carried them to the Old World, where some for example, opuntias, are now indigenous to desert regions there. They have a considerable fascination which is entirely their own: their figures, prickliness (or hairiness) and exotic flowers are all endearing and, moreover, they are not difficult to grow.

All the cacti described here are easy to manage, though quite different in appearance to one another.

The Rat’s-tail Cactus, as one would expect, produces slender, rounded hanging stems with a thick growth of spines and magenta-coloured flowers in early spring, each of which lasts for several days.

The Old Man Cactus is so named for the mass of white hairs, 12cm (5in) or so long, produced all over it. It comes from Mexico where it can grow to 12m (40ft) tall, but it is very slow-growing and will not flower until it is about 6m (20ft) tall.

Chamaecereus sylvestrii is often seen growing in pots on windowsills and is embarrassingly easy to cultivate; it produces prostrate sideshoots with ease and rapidity, and each of these can be removed and rooted with equal facility. It flowers profusely in May and June, producing bright red blooms.

The Golden Barrel Cactus, Echinocactus grusonii, is cheifly famous for its golden spines, the tuft of golden wool in top and deep yellow flowers. It is almost completely round and is found in the deserts of central Mexico. It is also slow-growing, and in cultivation rarely reaches a size at which it will flower.

Mammillarias are sometimes called Pincushion Cacti. They are often almost completely circular and covered in bristles, with small bright yellow, red, pink or white flowers peering through the bristles in a circle round the top of the plant. They last for several weeks and are often produced in intermittent bursts throughout the summer, followed by red berries which may last through the winter to the new flowering season.

The Prickly Pear (Opuntia) is the one most people start a cactus collection with; it is practically indestructible and grows new ‘ears’ almost overnight. But it rarely does more than this, and after a season or two of watching it rapidly outgrowing its space, it can be tactfully given away to an unsuspecting novice! you will at least have learnt the elements of cactus management from caring for it.


The compost required for cacti is rather different to the usual John Innes potting composts. They need very good drainage and you can use John Innes No. 1 with a sixth part of coarse sand added. Some of the coarse sand proportion can contain broken brick.

Alternatively you can use a mix of 3 parts John Innes compost to 1 part fine grit, or a mix of 2 parts loam, 1 part peat and 1 part coarse sand (all parts by volume). If you use the second mix about 112g (4oz) of a general compound fertilizer should be added to each bushel, or alternatively a sprinkling to each 7.5cm (3in) potful.

At the bottom of each container there should be the usual pieces of broken clay pot, brick or polystyrene.

Sunlight & Temperature

Cacti like as much light and sun as possible at all times, and are ideal for windowsills facing south; they will take any amount of heat. In winter the temperature should not drop below 4C (40F); if you can keep it at 7C (45F), that is better still. Dry atmospheres do not cause any trouble, so you need not spray or supply humidity.


Although cacti come from drought ridden areas, this does not mean to say that they will survive, grow or flower without any water at all. In spring and summer, they need watering almost as much as ordinary plants, giving them a lot when you do water and then leaving them severly alone until the compost surface is once more dry. In hot weather this may mean watering every two or three days.

As autumn comes, you will find that the compost is not drying out anything like as quickly , and you wil not need to water very often at all.

In winter – the cactus resting time – once a month will be sufficient, even less, especially if the temperature drops. Some people do not water at all between November and early March, but if the plants are kept in central heating they will probably need water every two weeks or so.


As well as water, cacti need food , like other plants, so the compost should always contain some to start with , and liquid feeding can be given in the growing season. A potash-high fertilizer, such as one of the tomato or rose fertilizers, should be given once a fortnight. This will encourage flowering, and prevent the plants from becoming too fleshy. When cacti do flower, the blooms are brilliant and exotic, and, contrary to myth, they by no means flower at night once every seven years! Instead they often flower every year for several weeks continuously.


Brown, red or yellow spots on cacti usually mean cold or wrong watering; a reddish tinge on young cacti means that they have had too much hot sun. Shrivelling shows lack of water and rotting at the basic indeicates too much water in winter.

Common Pests

Mealy bug or root aphis are the main pests.

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