Nutrients

Nutrients are a requirement for all life, including plants. While these cacti can survive for a good while with just soil, light, and water, eventually health issues will show up. It may take a season or longer to see impacts of nutrient deficiency or imbalance. pH of the soil and nutrient feed is also related, as the pH affects each nutrient's availability to the roots.

Pick up some Masterblend 3 part formula (Tomato & Vegetable/Epsom Salts/Calcium Nitrate), or for a more costly and slightly less optimal ratio single part, General Hydroponics Maxigro or Megacrop. Mix at the label rate and feed somewhere between every other watering to 4 out of 5 waterings when daily highs are in the 68-86F range, with the non feed waterings being a flush using pure water. Always flush and fertilize to at least 15% runoff.

The optimal elemental nutrient ratio expressed in N:P:K:Ca:Mg is 1 : 0.4 : 1.6 : 1 : 0.35. On fertilizer products sold in the US, P is expressed in terms of P2O5 and K is expressed as K2O, which can be verified by examining the label.

* P2O5 x 0.436 = P

* K2O x 0.83 = K

So for a US label product, the optimal N:P2O5:K2O:Ca:Mg ratio is 1 : 0.92 : 1.93 : 1 : 0.35. Micronutrients are also important. For a deep dive on where this ratio comes from, check out this forum thread: https://cactiguide.com/forum/viewtopic.php?t=47603

Masterblend 3 part is the one product on the market I have been able to find that most closely hits these ratios and at a good price too. The other two options mentioned above are slightly off on the ratios but close enough that they shouldn't cause any issues. Masterblend has the added benefit of buffering the feed solutions pH to a perfect 6.3 when mixed properly and allowed to rest for 3 to 12 hours before use. It should be prepared as follows: Dissolve 2 parts Tomato & Vegetable, 1 part epsom salts in the majority of the water. In a separate container, dissolve 2 parts calcium nitrate and then add to the rest. Do not let mixed fertilizers sit for more than a day as you may see algae or bacterial growth or you could have the components react and create a suspension, indicated by clouding, which would change the nutrient availability and pH.

If you are going to use synthetic fertilizers, you should really understand how to test your feed solution and soil.

I don't think that synthetic nutrients as discussed above pose any health risk whatsoever to people consuming crops treated with them or to the plants, if applied properly. Do you always purchase organic produce at the grocery store, and never eat out at that serve non organic produce? Synthetics offer more consistent and controllable nutrient levels and ratios with no real downsides. But if you are insistent on remaining organic, the best option is to use organic soil amendments which are added when creating your own soil recipe.

There are a varied assortment of other very helpful things to water or feed your cacti. To learn more about them, check out the Beneficials page.