If you need an easy care and forgiving houseplant, an ever popular Cactus could be the plant for you. Cacti come in many different shapes and sizes but in general can be separated into two groups, the Desert Cacti (which this article is based around) and the Forest Cacti (Christmas and Easter Cactus) however the care requirements for each group are very different.
The Desert Cacti have the same care requirements of good light, heat and a correct watering technique. They don't outgrow their chosen locations in your home or their pots particularly quickly, are quite cheap to purchase (when young) and require only basic maintenance. If you mistreat or are quite neglectful of your houseplants in general, a cactus will normally take more punishment before succumbing when compared to other houseplants. On the other hand if you are very attentive you will have a a fine specimen growing happily and potentially showing off some wonderful flowers.
They deal very well in homes with dogs, cats and children in terms of toxicity, however this is only achieved because of their protective spines which will hurt anyone or anything attempting to get at the plant flesh. In this sense they could be considered dangerous and care should be given in their chosen location to prevent pets or children getting a handful (or face full) of spines (if that ever happens read this).
Cacti protect their central parts so well because it's their primary means of storing normally scarce water and nutrients. If you water a very dehydrated cactus, within an hour you can almost see it swelling and bulging as it takes up the water.
As mentioned there is a wide range of cacti you can buy as houseplants, too many to list here individually. But all these names are popular plants and will often be seen on the pot labels Cereus, Cylindropuntia, Echinocereus, Echinopsis, Notocactus, Pilosocereus, Rebutia and Trichocereus.
In general there are two main shapes you can find, globular (picture up) and columnar (picture right). Cacti with a globular habit grow in a round ball shape so tend to be shorter but wider. The columnar cacti grow in a column shape so eventually become taller and narrower. If you plan on clustering several close together you can combine these differing looks effectively by mixing the shapes together in a small collection or by growing only one type for a very different but striking looking effect.
In the majority of cases, a cactus will be very happy to sit in a location that receives direct sunlight for part or most of the day. This is often essential if you want your plant to get bigger and to flower, for the those that do flower indoors of course as not all do. That said, almost all cacti will be somewhat accepting of a shadier spot for a time, but growth will suffer as a result.
The greatest cactus myth is arguably that "they don't need much water". On one hand this is perfectly true, there is no other type of plant that is so well adapted to deal with long periods of drought. If you forget to water once the soil has dried out it will most probably survive for several weeks or even months without any ill effects. However by doing this your plant has now become a surviving rather than thriving houseplant.
The greatest cactus myth is arguably that "they don't need much water".
Instead, the best way to water your cactus is to do so whenever the soil dries out fully from your last watering. When this happens water well again and then don't give any more until the soil has dried out once more. Give less water if your plant is in a colder or shady position and in Winter cut right back, just enough to keep the soil barely moist is plenty. Additionally in Winter if you have moved your plant to a cold spot for its rest period you may only need to water it a small amount once during the entire winter period, if at all.
Remember that deserts tend to be very arid with very low levels of humidity. So you need to be careful about providing too much humidity because cacti have an increased chance of rotting in very humid locations if combined with poor ventilation. So bathrooms and steamy kitchens might not be suitable unless the ventilation is good.
When it comes to feeding, a standard cactus or all purpose fertiliser during the Spring and Summer months will be suitable. These plants don't grow particular fast so you don't need to apply fertiliser to your cactus more than a few times each year.
Broadly speaking there is not an upper range of temperature you will find in your home or office that is too hot for your cactus. 5°C / 41°F is the lowest safe temperature, as you get lower the risk of serious damage increases. If the soil is barely moist or actually completely dry you could get closer to 0°C / 32°F or a little below in some instances, although some damage might result.
Despite their eventual size the majority of cacti have very little root volume compared to what you can see above soil level. The roots are often shallow rather than deep and therefore a large container for a small plant "to grow into" is often a mistake as it massively increases the risk of overwatering and rotting.
Young plants will need to be repotted every year or so to provide space for the roots to grow into. Once it gets to a large size you can reduce the frequency to 3 or 5 years intervals. You will want a good strong and heavy container for a very tall or mature cactus to prevent the container topping over. A lot of cacti growers will recommend clay pots as they are porous so will help prevent overwatering and allow the roots to "breath", however you can use plastic if you prefer. Be sure to provide fertiliser to any cactus which you are repotting on an infrequent basis.
When it comes to the growing medium or potting soil, you can use a wide variety of material from specially sold cacti compost mixes or DIY mixtures. What's ultimately important is that the potting medium needs to be "open" to prevent too much water from being held around the roots. Really heavy or rich mixes will keep a lot of water in place and encourage rotting, with this in mind you should also avoid using large amounts of "sand" as this can compact together overtime. Instead use something like horticultural grit or perlite to allow water to drain more freely.
You can take cuttings in Spring and allow them to dry for a few days to a week before planting them in a free draining mix and watering gently. However this isn't always practical if there are no cuttings to take, so these days propagating cacti at home is almost always done by seed.
It's simply a case of filling a pot with a free draining potting medium and then covering the surface with a small layer of grit or very small stones. Sprinkle the cactus seeds over the top layer and water gently before covering the pot with a plastic bag, like a tent, to keep the surrounding atmosphere moist and humid. Place in a bright spot away from direct sunlight and provide warmth to encourage germination.
Speed of Growth
Almost all true cacti grow slowly when compared to other houseplants. That's not to say they don't grow a reasonable amount (the tall column types can put out an inch or two of growth each year). However this isn't a good houseplant to pick if you are hoping for a standout striking specimen after only a short period, on the other hand it's a perfect companion for your windowsill as it won't outgrow this space for many years.
Height / Spread
Cacti come in so many shapes and sizes and because this article is quite broad it's very difficult to provide ranges. Some such as the familiar Saguaro can eventually reach over 40ft tall although when young it hardly grows and stays only a couple of inches tall for almost a decade. However Saguaro is rarely grown as a houseplant and instead you should follow the general rule that a shop brought cactus will take sometime before it starts to look vastly different to the day you brought it.
A lot of cacti do produce some amazing looking flowers in a large variety of colours providing you give them good conditions and care. For the majority this will be bright sunlight, regular watering and warm temperatures during the growing seasons. A period of rest is often needed in Winter too, which simply involves putting your cactus into a cooler spot and reduce watering to the stage where you are just giving it enough to prevent it becoming shriveled. All being well, plants grown from seed should flower by the time they are three or four, and then every year after. However a good many cacti simply won't flower indoors, so if it's essential to have a flowering cactus only buy a mature cactus that is already in bloom.
Grabbing hold of any cactus can be dangerous, the protective spines are there to provide defense to the plant and they aren't selective about what they will grab on to, stab or hurt. You must protect yourself when handling your cactus, such as when you are repotting it. Ensure you wear gloves, or if they aren't thick enough you can create a cardboard collar. Simply wrap the cardboard around your cactus and hold on to this to protect your hands.
But what happens when this doesn't work and you or your child or pet gets a handful of something nasty and you need to know how to remove cactus spines:
Large spines have the potential for more damage as they can puncture the skin and can go quite deep if they are long, however they are the most straightforward to remove if the wound is only minor. Simply pull it out with your fingers or a pair of tweezers. If the wound is serious or the spine is buried deeply you should consider seeking the attention of a doctor or vet depending on who's been hurt.
Glochid spines are much less likely to cause serious injury however they are thoroughly unpleasant. Unlike sharp visible spines they can look quite unthreatening to children, but glochids are actually tiny spines which resemble fine hairs that embed easily into the skin. Should that happen, individually they are hard to see and remove but if you rub against something or don't remove them all you'll know they're there! Clearly a good light and pair of tweezers are the best way to pull them out, but this may not be possible or it could be too time consuming if you're literally dealing with a handful. Instead you can remove them in mass by using duct tape, or PVC glue. Simply apply the tape or glue over the area and then quickly pull off the tape or peal off the glue (once it's dried), this should remove most of them. Either follow up with another round of tape / glue or use tweezers to deal with what's remaining.
If you see random brown scales on your cactus as shown in the middle of this picture then you could have a scale problem. At times someone may just assume it's a blemish on the surface, but quite often its actually a living Scale Insect. If you suspect your plant is under attack, have a read of our pest article for more details and help.
Rot at base
Likely basal rot disease. It typically happens to cacti when they're been watered far too much. There is no treatment, but if only part of the plant has been affected you can simply cut the rot out. if the rot surrounds the entire base of the plant then it can't be saved in its current form, although you may wish to try grafting it on to a suitable candidate or using the top half as a cutting.
Rot at base (not over watered)
This is usually caused by cold damage in the presence of quite damp soil. 5°C / 41°F is the lowest safe temperature when there is a reasonable amount of water in the growing medium. You should be able to get closer to freezing temperatures if the soil is very dry before this type of rotting will happen.
Brown growth on cactus
There are several things which may cause brown growths or sections to appear on your cactus houseplant so this can be hard to answer with certainty. It's doubtful you will be able to remove the browning once its formed, however here are some suggestions about what may have caused it and prevent it getting worse:
(Article / Gallery) Photo credit for the group of cacti plants by banana-kid
(Gallery) Photo credit for the ball cactus by Earthchild
(Article / Gallery) Photo credit for the globular cacti by Calvin Teo
(Article / Gallery) Photo credit for the flowering cactus by Paolo Neo
(Article / Gallery) Photo credit for the Opuntia microdasys by Christer Johansson
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