Growing Cacti and Succulents in the Greenhouse

Cacti and succulents add an exotic note to every collection of greenhouse and indoor plants. Once known as the `Cinderellas of the plant world’, their popularity is now assured. With a little care they can be induced to grow well and produce flowers of astonishing variety and colouring. Here we look at the different types of cacti and how they can be grown successfully.

Succulents are plants that have evolved with the ability to store water in their leaves, bodies and roots to enable them to survive periods of drought. They are more common than most people realize — in fact, most countries in the world have some form of succulent plant in their native flora. Even in Britain, sempervivum (houseleek) and sedum (stonecrop) are quite often seen even though the climate does not seem to warrant succulent growth.

One of the largest families in the succulent flora is the CACTACEAE, or cactus family. Cacti differ from succulents in having areoles from which their spines grow and from which, in many cases, the flowers are produced. These areoles look rather like small felt pin cushions; the spination of the other succulent plants resembles thorns.

It is believed that both cacti and other succulents originated from a common source before the continents of Africa and America parted in the continental drift many millions of years ago. Today cacti are native to North and South America, but succulents, though mainly indigenous to Africa, can be found growing native in many other parts of the world.

Types of cacti

There are two completely different types of cacti: the epiphytes and the so-called `desert’ cacti. Both groups require separate forms of cultivation as their habitat is so different.

schlumbergera-Christmas-cactus The epiphytes (or ‘jungle’ cacti) that include such well-known plants as schlumbergera (formerly zygocactus), the Christmas and Easter cacti, epiphyllum, rhipsalis and so on, are flat-stemmed plants growing in the tropical rain forests of Central America. They do not live on the ground but on the branches of forest trees, in crevices and joints that have accumulated leaf mould and bird droppings. Their stems and roots obtain moisture from rain and they are continually shaded from the tropical sunshine by overhanging branches.

The second type is the so-called ‘desert’ cactus; the name is slightly misleading as the true habitat of these plants is not desert but a form of heathland with grass and small shrubs. They are native to North and South America but seem to adapt well in other places; too well in some cases — as in Queensland, Australia, where the opuntia (prickly pear) invaded vast areas of farmland and defeated all efforts at eradication until its natural predator, the caterpillar of the cactoblastis moth, was imported. These cacti inhabit areas of little rainfall but have powers to absorb water when it is available and retain it for future use when times are dry and hard. Sometimes they can absorb moisture from morning mists through their stems and spines.

General cultivation

In Britain most cacti are grown in greenhouses or garden frames, as the winters are too damp and humidity causes the plants to rot if they are planted outdoors. Cacti will withstand a habitat that has very cold, but dry, nights and winters, but cannot survive a damp, cold atmosphere.

Some gardeners still use clay pots for growing cacti, but most have now changed over to plastic, as these are lighter on the greenhouse staging and easier to keep clean, especially for exhibition purposes. Also, plants in plastic pots do not require watering so often.

Composts used for growing cacti and succulents must be particularly porous, such as J.I. No 2 or 3, to which you should add some very sharp sand, grit, or broken brick to ensure good drainage. This is very important, especially when growing in plastic containers. The pot size should be as large as the diameter of the plant with its spines plus a further 13mm (-1- in) all round. The epiphytic cacti will require the addition of humus to the potting compost in the form of leaf mould, peat or well-rotted manure, and again the soil must always be well drained.

Whereas the ‘desert’ cacti will grow well in full sun provided there is sufficient ventilation, epiphytes, being ‘forest’ cacti, require shading from sun from early summer to mid autumn (May to September), and can only be grown on top of the greenhouse staging during the winter months. Evidence of sunburn shows as red pigmentation on the stems; affected plants should be shaded at once. Never stand the pot in a container of water as they cannot tolerate bog-like conditions.

How much water?

How much water to give and how often to water are key questions with this group of plants, and it is difficult to give an easy answer. Common sense plays a great part here: if it is hot and sunny, plants growing under glass require a great deal of water. Those growing in clay pots may need water each evening. Be careful when watering not to leave any droplets on the crowns of the plants, as this could cause scorching when the sun comes out, and badly damage a plant; this is one reason for watering in the evenings and not during the day. If the weather is overcast or damp the plants will not require much water. Desert cacti rest during the winter months and need very little water then, although overhead spraying from time to time can be beneficial. Some succulents can grow in the winter and rest in summer, and it is as well to know the plant’s habits and treat it accordingly.

Cacti and succulents grown indoors should be treated as ordinary house plants; they will require watering during the winter (especially if there is central heating) otherwise they will dehydrate. Also if they are kept on a windowsill, and there is frost, bring them into the room, inside the curtains; cacti and succulents will not withstand damp frosts. A quite large plant will go to pulp overnight and is a heartbreaking sight next morning when the curtains are drawn back.

How much heat?

Cacti and succulents require heat during the winter, but remember that they hate a stagnant, stale atmosphere because it causes fungus and rot. So even during the winter provide the plants with some fresh air on a sunny day.

If you heat by paraffin, remember that for every 5 lit (1 gal) you burn, the same amount of water vapour is produced. Even so, many people find heating by this method satisfactory, providing that the appliance is well maintained, and not in a draught. It is very sad to see a collection covered in black, oily soot where a stove has flared. This is also very difficult to remove and it takes years for the plants to grow out of the effects.

Electricity is clean and easy, but unfortunately very expensive. Under-soil cables are very good, but costly to run and install for a complete collection; this method is favoured for seed-raising and for the propagation section, where plants are put to root. Fan-heaters create a very dry heat, so spraying will have to be done occasionally during the winter when it is sunny or the plants become dehydrated. With a special type of electric water heater that gives off steam when it boils, spraying is not required. Should there be a power failure for any reason, a certain amount of heat will be retained in the pipework, providing the power cut does not go on for too long.

Gas heating for the greenhouse is becoming very popular but be sure that you can obtain spare parts should anything go wrong. Laying a gas supply to the greenhouse could prove to be costly if it is any distance from the house, especially if it necessitates taking up cement paths as well.

Lining your greenhouse with sheet polythene provides a form of double glazing during the winter, and cuts down heating costs appreciably. If you do decide to fit this, make sure that the sheets are overlapped in such a way that the condensation will not drip onto your plants and cause rot, but run down safely out of harm’s way.

12. July 2011 by admin
Categories: Cacti and Succulents, Greenhouse Gardening | Tags: , | Comments Off

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