All plants benefit from a little help from time to time, and cacti and succulents are no exception.
The perceived wisdom in the hobby is that cacti and succulents require low nitrogen fertilizer because anything else may result in unnatural growth. However, while high nitrogen is deleterious, there’s no real evidence for low nitrogen and some growers favour a balanced formula.
What’s important is NPK – nitrogen, phosphorus, potassium – and this ratio varies between fertilizers. Having looked into this I have compiled a table which illustrates this point:
The product that stands out is Baby Bio which is a definite no for cacti and succulents as the nitrogen content is very high. If you grow tomatoes you can use quarter-strength Tomorite®, a low-nitrogen feed. There are a number of ‘cactus fertilisers’ available from garden centres which will be perfectly OK and tend to have particularly low nitrogen content.
The products usually recommended by the BCSS are Chempak 4 and 8 which only differ in their phosphorus levels (they come in 800g packs). Chempak’s own cactus and fertilizer has very low nitrogen, whereas their ‘fully balanced’ product is the same as Miracle Gro (not sure why that’s so miraculous!).
Back in the 1970s when Phostrogen was first marketed, the late Edgar and Brian Lamb became great proponents and if you want a fertilizer with a bit less nitrogen this may be the answer.
When to use fertiliser
In the end it comes down to personal choice, as does the frequency of application. Whatever you choose, it is generally easier to apply a dilute solution at every watering rather than, for example, full strength every fourth watering. This is something that Chempak suggests and is what I do, but in the height of the summer when it’s particularly hot and I water more frequently (and cactus growth usually slows) I leave it out altogether.
Whatever product you use, don’t over-fertilise.
Windowsill, Conservatory or Greenhouse?
Growing outdoors
Watering
Compost
Pots & containers
Top dressing
Potting up
Fertilizer
When things go wrong