Caring for Cacti

The below are the very basics of growing cacti indoors and out - please don't hesitate to get in touch via our contact page if you require any specific advice and I'll do what I can to help!

The Growing Year - Watering

While cacti aren't famed for being tricky to care for, there are a few key guidelines worth bearing in mind in order to (hopefully) give your plants a lengthy, floriferous and happy existence.

Indoors

Keeping cacti in your home all year requires a bit of consideration of light levels as the year progresses, if you live in gloomy old England like me then the winter is a fairly low light environment, especially when the watery light has then passed through a pane of glass and made it to your plants sitting there on the sill.

With this in mind, if plants are kept in a centrally heated room and watered over winter they tend to develop weak, etiolated and unattractive growth, something like in the photo below.

To keep your indoor cacti happy and rot free I'd therefore recommend the following for those kept in the home all year round:

Growing

During the growing season (i.e. April/May - mid Septmeber) keep your plants in a very sunny position, close to the glass of the window.
Water around once every 10 days - the idea is to drench the plant, with water running out of the drainage holes, and then allow to fully dry out, ideally then sitting for a couple of days completely dry before watering again. This is highly reliant on using a good free draining substrate - see the bottom of this page for more on appropriate growing media.
Feed with dilute low nitrogen feed every other watering (half strength tomato feed is fine for this).

Resting

When temperatures start to drop (i.e. mid September in the UK), slacken off the watering, aiming to stop by mid October / November.
When finished watering, move the plants to a cold (but frost free), dry environment. An unheated porch or conservatory is ideal. Plants need to be kept cold so they go dormant and rest, and critically must be kept dry.
If a centrally heated room is the only option, slacken off the watering to a trickle every month or so, allowing the plant to dehydrate significantly.

Outdoors

Growing cacti in a greenhouse or polytunnel is much simpler than growing in the home, and the plants seem to appreciate it too! As a basic start to 'growing under glass', follow these steps:

Growing

During the growing season (i.e. April/May - mid Septmeber) keep your plants in a very sunny position in the greenhouse.
Water around once every 10 days - the idea is to drench the plant, with water running out of the drainage holes, and then allow to fully dry out, ideally then sitting for a couple of days completely dry before watering again. This is highly reliant on using a good free draining substrate - see the bottom of this page for more on appropriate growing media.
Feed with dilute low nitrogen feed every other watering (half strength tomato feed is fine for this).
If temperatures get very high (40c+) then be cautious with watering, many species will effectively go to sleep in these conditions, and watering can cause rot. I often skip a watering during an exceptionally hot period.

Resting

Slacken off watering as soon as summer temperature start to drop, generally finishing watering completely by mid October.
Keep plants fully dry, but otherwise in the same position until the spring.
Keep frost free - generally a minimum temperature of 2c is good. Better they stay cool than get really warm over winter. Many species will happily survive sub zero temperatures if kept completely dry, but a 2c minimum is a good guideline.
Start watering again as warm spring days come round again, generally April-ish.

That's really all there is to it in terms of watering, to put it in simple terms, regular watering and heat in summer, and cool and dry in winter. Remember - if in doubt, don't water, being dry won't do your plants any harm, but being too wet will!

The above are only guidelines however; many trickier species either require higher winter temperatures or more carefully moderated watering regimes - so think a bit more carefully if growing genera such as Matucana, some Melocactus, Uebelmannia, Sclerocactus and epiphytic cacti.

Substrate

The 'best' sustrate for growing cacti in is a hotly argued over topic among cactiphiles, with many experienced growers having their own favoured recipe for potting their plants.

Up to a point however, some basic generalisations can be made to help new growers with substrate.

Avoid bagged garden centre 'cactus soil' mixes like the plague! they are invariably claggy and poorly draining, and generally only effective in killing cacti!
Avoid using peat in any potting mix; besides the appalling environmental issues associated with peat extraction, it is far too water retentive to grow cacti in - how many cacti grow in peat bogs after all?
Drainage, drainage, drainage! Unsurprisingly, drainage is key when growing cacti, and for many species its hard to have a mix which is too free-draining.

Among the popular ingredients of cacti growing substrates are the following:

Grit - almost goes without saying as a drainage improver. Comes in many varieties, I find that relatively small grained sharp grit is best. Decomposed granite (otherwise known as 'cornish grit') is among the best. Also worth trying is chick grit, sold by agricultural suppliers for chicken farming but generally cheap, plentiful and efffective. Take care however to avoid chick grit with oyster shells included, as this tends to have a very high pH not suitable for many species.
Moler Clay - this is most readily available as clay cat litter in the uk; at the time of writing a brand called "Sophisticat pink" is easily obtained in pet shops/supermarkets. This is an exceptionally good substrate, and very highly recommended by myself and many others; it drains very freely but holds a little water to spur on good growth in most situations. Also available as moler clay oil spill absorbent granules under brand names such as "New Safety Tread" (which also lack the rather intense but harmless smell of the cat litter).
Pumice - this is used extensively by bonsai growers and on the continent for cacti growing, and is reportedly very good. I've never used it as it is hard to find and expensive in anything other than small quantities in the UK. If you can get it, it would be well worth a go.
Sands - large grained sharp sand can be included in mixes, and some growers are very keen on it, personally I find sand can actually impede drainage in many situations so tend to prefer larger grained grits. Avoid fine sand at all costs as the waterlog and kill cacti pretty quickly!
Perlite - a good inclusion in many mixes if preferred. The only real disadvantage is that it tends to float to the surface and blow away when watered and can be very messy!
Soils - a bit of good old dirt is generally advisable in most mixes to keep plants fed. Worth reiterating - do not use peat! I would recommend a good sandy loam topsoil, preferably screened to remove sticks and lumps.

With the above in mind - the basic mix I use and can strongly recommend is as follows:

Approx 40% sharp griit (I use decomposed granite or small grained flint grit)
Approx 40% moler clay (cat litter /oil absorbent)
Approx 20% screened sandy loam.

That's all there is to it, happy growing!