Hi ChaoticN,
A few things to unpack here...
First, go with crushed granite poultry grit instead of aquarium pebbles. You can buy it on Amazon, although maybe too expensive if you have a lot of plants. If that's the case, look for the possibility that you can buy crushed granite at a local nursery or feed & tack store selling poultry supplies.
Regarding fertilizers, see this:
viewtopic.php?t=47603
I realize there's a lot of detail in my presentation, but worth taking the time to read through it thoroughly. Regarding nutrient ppm numbers in your watering solution, nitrogen is the benchmark that tells us if we're overfeeding our cacti and succulents. 40-60 ppm N per feeding is good, between 60 and 90 ppm is okay. Anything above 90 ppm per feeding, and cacti end up with something called "nitrogen bloat". If the amount of N they get is within the optimal 40-60 ppm range, everything else falls into place
if the P and K balances and dosages are right. You'll see this issue being discussed in my presentation.
I'm working with a member in Indonesia who needed help with his fertilizer, and part of the discussion dealt with the important role calcium plays in plant growth. I'll pull out something I said there -- a lesson learned from hydrobuilder.com:
- "Calcium has a similar role in plants as in humans, helping produce strong cells and root walls. This leads to stronger plants. We've recently come to understand that calcium is actually the dominant nutrient in most plants." [My emphasis]
This is certainly true for cacti and succulents, although we should know that magnesium is also important (but in smaller amounts). Believe it or not, the hardness in tap water can provide Ca and Mg to plants, but there's a problem -- Ca and Mg are "locked out" by carbonates in the water. Solution -- acidify. The 2 acidifiers safe for home use are 5% white vinegar and citric acid. For growers with big collections, citric acid is better than vinegar because it's more concentrated. The reaction products of acidification:
- Calcium acetate and magnesium acetate from vinegar.
- Calcium citrate and magnesium citrate from citric acid.
Acetates and citrates are highly soluble in water, so either one of these avenues makes Ca and Mg available for uptake by the roots of your plants. Back in 2019, I posted a "how to" guide on acidification, but the info is
really outdated, so I'll put a new one together soon.
Getting back to the subject of fertilizers -- I became a huge fan of hydroponic ferts when I went soilless in 2012, and I highly recommend them because their nutrient profiles tend to be more comprehensive than what we'll get from dry water-soluble ferts. After Dyna-Gro discontinued the 7-7-7 I was using, I went over to General Hydroponics FloraMicro 5-0-1 and FloraBloom 0-5-4. Put 'em together, and we get 5-5-5. Only problem there, P is too high and K is too low in relation to N, so I struck the right balance with ammonium sulfate and potassium sulfate. Add in some nitrogen-free Cal-Mag from TPS to supplement the Ca and Mg my cacti are getting from acidified tap water. If you'd like to do the same, I'll be happy to give you the "recipe" and instructions. If you'd rather go with a different fert, look for one with equal NPK numbers (7-7-7, 10-10-10, etc.), and I can help you with the supplements that'll give you a well-balanced feeding regimen for your plants.