FEEDING YOUR SUCCULENTS
Fertilisers is a pretty complex subject with lot's of competing claims from different manufacturers.
Let's look at fertilisers for succulents and cacti and try to make sense of it.
Succulents and cacti do not generally require a lot of added nutrient by way of fertiliser applications. They are adapted to tough conditions and will grow happily (in most cases) without fertilising.
But. They will do better if they are fertilised, provided you don't overdo it.
Fertilisers are usually compared on their N-P-K.
Nitrogen, Phophorous and Potassium (K).
The ‘big three’ nutrients required for plant growth and health^
It is often considered that an NPK ratio* of around 3:1:2 is fairly consistent across the plant world in providing the N, P & K that plants require in the right ratio (and therefore not providing too little or excess in any nutrient in particular) and that this ratio differs very little between plants
(3:1:2 means about 3 times as much N to P, and about twice as much K to P).
So, does the 3:1:2 ratio work for succulents and cacti?
So, what’s readily available on the market here in Australia?
Pre-mixed, ready to use soluble fertilisers
- Maxicrop Succulent & Bonsai Food
- Scotts Osmocote Pour & Feed Cacti & Succulent
Both these products from reputable brands are marketed as containing lower N and higher Potassium (K).
(I couldn't see anything on the Scotts product in terms of actual analysis to confirm this, they simply state this is the case).
In the case of the Maxicrop the NPK ratio is 1.5:1:4.2
This is good.
As Scotts point out, the low N/high K promotes steady growth and good flowering. With flowering think cacti especially.
May not be the most economical way of fertilising but being pre-mixed they are totally hassle free and a great option for smaller plant collections.
Soluble fertiliser - dry (requires mixing in water)
- Searles 'Flourish' Cacti & Succulent Soluble Plant Food
Contains trace elements in chelated form. Chelated is good, absorption by the plant is excellent with chelated.
NPK ratio is 3.7:1:5 so, relative to the '3:1:2' ratio you can clearly see Searles have upped the ratio of Potassium (K).
Granular controlled release fertilisers
- Scotts Osmocote Controlled Release Fertiliser - Cacti & Succulent
- Searles Robust Cacti & Succulent Fertiliser
NPK ratio's of 11:1:13 & 7:1:6 respectively.
Although high ratio's of N, the controlled release of nutrient over 6 months (in the case of these particular products) means the plant isn't getting bombarded with nutrient.
Controlled release fertilisers (as opposed to slow release, which is technically a different thing) are pretty cool.
The coating on the prill (granule) acts as a permeable membrane allowing water inside the granule (osmosis) and nutrient in solution, dissolved by the water, out (diffusion).
The thickness of the coating has a big impact on release rates, and as such release rates up to 12 months or more can be achieved.
But what's really awesome is that the micro-pores in the coating expand as temperature rises allowing more diffusion of nutrient out, so more is released when the plants need it and less in cooler weather.
Granular controlled release fertilisers are a good option in larger outdoor gardens, especially if the thought of mixing up large quantities of soluble fertiliser each time doesn't appeal!
Just keep in the back of your mind though that if higher temperatures (in conjunction with moisture) increases the rate of release of nutrient from the granule this will mean summer dormant plants will get nutrient at a time of year when they are not actively growing.
For summer dormant plants I would suggest you are better off applying at the start of autumn to feed the plant heading into winter and, given the 6 month release pattern and low diffusion rate over winter, there should be residual available to the plant the following spring.
IMPORTANT
If you are using a succulent and cacti potting mix that meets Australian Standard AS3743, check on the packaging what controlled release fertiliser it may contain. If it has then confirm how long that will provide nutrient for ie; 1mth, 3mths etc.
Because you don’t want to fertilise if there is still ‘viable’ fertiliser in your potting mix.
Finally, If in doubt over the appropriate application rate for a particular product, we recommend you contact the manufacturer direct for clarification.
And remember, when it comes to succulents and cacti LESS IS MORE!