BCSS - Forum

As a generalisation, succulent plant growers will tell you to use a low-nitrogen fertilizer for your plants, but is it possible that we are not making enough nitrogen available to our plants?

Nitrogen in liquid feeds can be in two forms: either inorganic (nitrate and ammonium ions) or organic (urea). There are two separate pathways by which nitrate and ammonium ions are absorbed into plants, but generally speaking (there are always exceptions) urea cannot be directly taken up by plants. Urea has to be broken down by soil micro-organisms into inorganic nitrogen before it can be absorbed.

So are these micro-organisms present in pots of soil we use for our succulents? It has been suggested that they do not develop well under our conditions because (1) we start off with sterilised compost anyway and (2) the wet/dry cycles that we use when growing succulents are not conducive to the survival of the micro-organisms. Many people are now using purely mineral potting media such as moler clay, pumice or even just grit, none of which can readily support the micro-organisms.

If this conclusion is correct, then liquid feeds which are largely based on urea as the nitrogen source would not be effective for our plants. For years I have used Phostrogen (NPK 16:10:24) as my liquid feed, but reading the small print I find that the 16% nitrogen is 14% urea and only 2% inorganic nitrogen. My plants could therefore be struggling with nitrogen starvation. We would probably not use Miracle Grow because it is high nitrogen (NPK 24:8:16) but 20.5% of that 24% nitrogen is also urea.

My conclusion is that I should now use one of the Chempak products for my succulents because the nitrogen in these is largely inorganic. Chempak 4 (NPK 15:15:30) has the 15% nitrogen in the form of nitrates 8.5%, ammonium 3.0% and urea 3.5% while Chempak 8 (NPK 12.5:25:25)[corrected as per message below] contains only inorganic nitrogen as nitrates 7.6% and ammonium 4.9%. Chempak Cactus & Succulent fertilizer was not on the garden centre shelves when I did my research yesterday but Vitax Cactus feed (NPK 10:25:25) was completely inorganic nitrogen. Composition of the Vitax is obviously similar to Chempak 8 but much more expensive.

So what are the opinions of you other growers, particularly if you use purely inorganic media? We should probably be more careful with our selection of fertilizers rather than just saying "low nitrogen".

I don't have an entirely mineral soil but I use sodium nitrate as the N source. I use that mixed with low N fertilizer to get the P K and trace elements. The result is fairly balenced NPK. I use this mix rather than a pre-mix balenced feed so I can get a nitrogen source that is not urea.
I also add some epsom salts and also I fiddle my tap water to have pH of about 5.5.
I changed to this pH and feed regeme a couple of years ago and my cacti are growing better than ever. No sign of over-lush growth from a balanced feed but then my rates are low.
I hardly feed my mesembs at all. I just repot regularly every decade.
David Lambie

Just a correction: Chempak #8 is 12.5:25:25. I know because it is my first choice of fertiliser so it's sitting in my cupboard. I do use others from time to time, as narrow faddy diets aren't good for anyone

I've used chempak 8 for a few years for the reasons you mention Terry. I first became aware of the issue in relation to orchid cultivation, epiphytic orchids similarly can't utilise ureic N effectively. I've certainly noticed better growth and flowering since switching from phostrogen


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First watering will have a bit of white vinegar and some Ammonium Sulphate if I can get some help carrying the watering can, later in the year I will use phostrogen as I have a feeder that fits on the hose pipe which I can manage by myself.

Chempak No 8, have used it for as long as I can remember.

Chempak No 8

I've mentioned this before in a half joking fashion. It is for seed growing, rather than adult plants, but the best ever germination and subsequent growing rates for seedlings I've ever had was when I re-used the gravel from the bottom of two fish tanks. Everything came up like the proverbial mustard and cress and grew really well.

What would be the fertilizer present in this case - from a chemical - rather than literal point of view .

In my cat litter/grit mix the Mexican cacti get Chempak 8, my South Americans Miracle Gro ericaceous, with everything getting a watering with Chempak High Nitrogen fertilizer (can't remember the number) a couple of times each season.

Ideally you'd do a soil test first before deciding on a fertilser regime.

There's no point having a fertiliser high in N, P, K or whatever if your soil already has enough.

Too much of any of these, or any other element for that matter, can be as bad or worse than none at all!