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Succulents are an increasingly popular group of houseplants. They are often compact, are usually very easy to look after and are tolerant of some harsh interior conditions. Not only that, but they are visually striking and will always be a talking point.
For many, the terms cactus and succulent are interchangeable. However, whilst most cacti are indeed succulents, not all succulents are in the cactus family.
What are succulents?
Succulents are drought-resistant plants that are adapted to dry conditions. They can be found all over the world and are from a wide variety of plant families.
Succulents have modified tissues that are unusually thick, swollen or fleshy, which are used to store water. Such tissues may be leaves, stems or even roots. The word succulent is derived from the Latin word sucus, which means juice or sap.
Typically, they are adapted to high temperatures (although some are remarkably hardy) and most have evolved in conditions of harsh sunlight.
In order to capture and conserve the limited and unreliable water found in their natural habitats, succulents have a number of water-saving features, including:
- Crassulacean acid metabolism (CAM) to minimize water loss – this is a way to capture carbon dioxide (used in photosynthesis) at night for storage inside the plant until it is used when the hot sun shines during the day. The pores (stomata) on the leaves and stems only open at night, which reduces the amount of moisture that can escape.
- Reduction in the number of stomata to reduce water loss through transpiration
- In some plant families, the stems are the main site of photosynthesis instead of leaves (there is more than enough light available in their natural habitat, so leaves can be reduced or eliminated altogether)
- Distinctive growth form, including a reduced surface area:volume ratio (this means a compact, reduced, cushion-like, columnar, or spherical growth form) and absent, reduced, or cylindrical-to-spherical leaves
- Ribs enabling rapid increases in plant volume and decreasing surface area exposed to the sun
- Hairy or spiny outer surface to create a humid microclimate around the surface of the plant. This reduces air movement near the surface of the plant and reduces water loss. Spines and hairs also create shade and can even trap moisture from condensation (dew or fog)
- Waxy surface to reflect extreme solar radiation (often blue, white or pale grey)
- Roots very near the soil surface, so they are able to take up moisture from very small showers or even from heavy dew
What is the difference between cacti and succulents?
For many, the terms cactus and succulent are interchangeable. However, whilst most cacti are indeed succulents, not all succulents are in the cactus family. Cacti, however, have some unique features that distinguish them from other succulents.
The cactus family originates in the Americas (although species of Rhipsalis, such as Rhipsalis baccifera, or the Mistletoe Cactus, is found naturally in Africa and Sri Lanka - possibly as a result of seeds being carried by migratory birds). Many other species have been introduced and are naturalized in Africa and Europe: the prickly pear (Opuntia) is a common site in Spain, Portugal and North Africa.
Almost every species of cactus has dispensed with true leaves, replacing them with spines (although in some species, such as the Christmas Cactus, the stems are flattened and look very much like leaves). Some species, such as the prickly pears, have true leaves when the plant is young, but these are reduced and disappear completely as the plant grows. This means that photosynthesis occurs only in the stems. Cactus spines, hair and flowers are produced from specialized structures called areoles, which are a kind of highly reduced branch. The flowers are tubular, multi-petalled and often very brightly coloured. The spines and hairs help prevent water loss by reducing air flow close to the cactus and providing some shade, and they also protect the plants against browsing herbivores.
Image above shows typical cactus areoles.
Some cactus species are epiphytes (which means they live on trees) and they can be found in tropical forests. The Mistletoe cactus and Christmas Cactus are good examples, and they can cope with much lower light levels than more typical desert species.
Other types of succulent, which come from many different plant families, have adapted to desert life in different ways - often by changing the shape and form of their leaves. These include plants such as aloes and agaves, with very thick sword-shaped leaves (shown first below), or the weird-looking living stones (Lithops), that are effectively just two thick leaves close to the ground with a flower (shown second below).
Image: Agave showing thickened leaves, blue, waxy covering and sharp leaf spine.
Image: Lithops (living stones) - tiny succulents from Southern Africa
Do all succulents come from deserts?
Most succulents originate in deserts or semi-deserts, but some are found in places that are actually quite wet, at least for part of the year. The succulents from these places might be epiphytes - plants that live among the branches of trees and which do not root into proper soil, or they might be plants from places that subject to significant seasonal variation in rainfall - some subtropical environments with definite wet and dry seasons. Sometimes, the plants are described as semi-succulent, and they may become more succulent during times when water is less plentiful.
How to care for succulents
Succulents are amongst the easiest of houseplants to look after. They can tolerate periods of neglect and are ideal if you are frequently away from home. They tend to be untroubled by pests and need little in the way of fertilizer or water.
Most succulents require little in the way of water, and can tolerate erratic watering schedules. Succulents that grow naturally on the ground (as opposed to epiphytes) do best with a coarse, well-drained soil mixture. They often have shallow root systems which grow close to the soil surface, so they prefer to be top-watered rather than bottom watered - just be careful not to drench them when you do add water.
Epiphytes, such as Rhipsalis baccifera - the mistletoe cactus, or the semi-succulent Peperomia “Happy Bean” (shown below) are from rain forests and cloud forests, so as well as benefiting from a little more water than desert plants, they also appreciate having their foliage misted with tepid water as well.
Temperature for succulents
With the exception of semi-succulents from the rainforests (which are not at all cold tolerant), most succulents are able to manage temperatures that fluctuate from very warm to almost frosty. In the wild, desert air temperatures can drop to a few degrees above freezing at night and rise to well over 40°C in the middle of the afternoon.
Some succulents and semi-succulents, such as Zamioculcas zamiifolia (the ZZ plant), Sansevierias and Crassulas are less tolerant of cold temperatures and should be kept in spaces where the temperatures don’t fall below approximately 10°C.
Light for succulents
A good rule of thumb to judge light requirements is to look at the colour of the foliage, and whether there are dense woolly hairs on the plant.
Plants with a blue, grey or white waxy coating, or with quite dense hair, come from highly exposed, bright locations, and they use these features to reflect the intense light and heat that they experience like a natural sunscreen. The wax must never be removed, so be careful when cleaning the plants. Don’t rub the plant, just a little light brushing or dusting will be sufficient.
Image: Echeveria runyonii showing waxy bloom on foliage
One critical point to make about light, however, is that most succulents MUST have a period of darkness every day to allow their stomata to open. This is due to the way that these plants photosynthesize - they can only take in carbon dioxide at night (which is converted to malic acid for storage) to reduce the risk of the plants being dried out during the heat of the day. When it gets light, the stomata close tight, which prevents water loss, and the malic acid converts back to carbon dioxide inside the plant ready for use as a raw material of photosynthesis.
A little fertilizer for your houseplants is always beneficial, especially when the plants are about to flower. However, the key word here is “little”. Use a weak solution of fertilizer added to the water when you give your plants a drink, but don’t worry if you forget. Most succulents are very slow growing and have little need for much fertilizer.
Pests and diseases
The foliage of most succulents is pretty tough in order to keep moisture inside, so sap-sucking pests have a hard time making a living on these plants. Sometimes mealybugs are able to exploit a soft spot, especially on newly-emerging leaves and stems, but these are easy to pick off when you see them.
Diseases are also pretty rare. Most fungal and bacterial diseases need damp conditions to get a grip on their hosts, so the dry conditions favoured by succulents and cacti mean that they are rarely a problem.
As a rule of thumb, do not be tempted to prune cacti and succulents. One misplaced cut and you might expose the plant’s flesh, which could lead to it drying out.
Succulents with obvious branches, or joints in the stems, can be pruned to shape as long as you cut at those joints. However, if you are tempted to prune a succulent Euphorbia, you must be very careful as the sap is very irritating and can damage the eyes. The sap is sometimes under quite high pressure and can squirt out of the plant, so you must keep your eyes protected.
Succulents for the home
There are many hundreds of species of succulent that make for excellent houseplants, and it is very easy to get hooked on them. At foli8, we have a selection of succulents that can be the start of a collection, and the range is likely to expand in the future.
Here are some of our favourites: