Just to set the table for this little presentation, I grow the vast majority of my cacti in a 60% pumice/40% granite gravel mix -- essentially a hydroponic approach, so I have to fertilize every time I water. My fert of choice is Dyna-Gro All-Pro 7-7-7. The soil-less mix and 7-7-7 have been a winning combination ever since I got away from a soil-based mix in 2012. Here is the All-Pro's chemical analysis:
Recommended dilution for cacti and succulents is 1/2 tsp. per gallon of water. Here in the US, P is reported as P2O5, and K is reported as K2O. However, the Oxygen in P2O5 and K2O has no nutrient value, so the true elemental NPK available to our plants is 7-3.052-5.81. Since P should be lower than N, that's a good balance, but K should be about 1.5 times higher than N. Without getting into the technical details, I'll just mention that I add the right amount of Potassium sulfate when I whip up a gallon of watering solution, and the improvements with higher K have been amazing. Calcium and Magnesium are important minor nutrients, so the 2% Ca and 0.5% Mg in the 7-7-7 is not only a good balance, it's also a pretty good amount. However, as MikeInOz said in several posts elsewhere, there's no such thing as too much calcium. That being the case, I decided to up my fert game with the addition of a Cal-Mag supplement starting in June. And here's what I selected:
A few FAQs from the TPS website (https://tpsnutrients.com/products/calmag-oac):
- What is CalMag OAC made out of?
We start with a highly pure and organic source of magnesium and calcium. We then micro-chelate it with organic acids and a plant extract package. The result is the most bioavailable CalMag in the gardening and hydroponic industry. One example of this is that when this CalMag is used in soil it is 10+ times more effective at uptake than nitrate calmags.
- Is there Iron in CalMag OAC?
Yes there is iron, as well as an array of other micros. The NPK is 0-0-0 and the mineral breakdown is as follows: Nitrogen: 0% Calcium: 4.5% Magnesium: 1.1% Boron: 0.005% Copper: 0.007% Iron: 0.01% Manganese: 0.01% Sulfur: 0.05% Zinc: 0.01%
- Does CalMag OAC need to be shaken before use?
A shake before use is a great idea, though not required. The amino acids from the plant extracts in CalMag OAC can bind up over time. If you give it a shake they should reintegrate into the solution. If you mix feed water with the aminos stuck together, it's not a problem. The vigor of watering and mixing your feed water will disperse the aminos again.
- What is the shelf life of CalMag OAC?
CalMag OAC is guaranteed for 18 months from date of purchase, though it doesn't really expire. We recommend shaking up older bottles before use to mix the amino acids back into solution.
If you'd like to try the TPS CalMag, there are a couple of things you'll need to be aware of:
- When you prepare your watering solution, your primary fert of choice should go in first and the TPS fert supplement should go in last. Be sure to shake your watering solution thoroughly before you water.
- You'll need to water your plants right away. Unfortunately the TPS product precipitates out if you let leftover watering solution sit in the container for more than a few hours, and there's no way to get it back in solution.