Unless he knows how much Mo is being released every time he waters his cacti, that's the unknown variable I mentioned earlier. We're at a disadvantage because Dyna-Gro ferts are general-purpose products, and based on a conversation I had with one of the Dyna-Gro people, they don't know if cacti need more Mo for efficient Nitrate-to-Ammonium conversion in the plant. With that said, here's a thought experiment, although it'll require making 3 assumptions:MikeInOz wrote: ↑Mon Jan 23, 2023 6:23 am I would stick with the Dyna grow because it has more ammonium. But either one would probably be fine. My cacti get double the ammonium/urea N than Nitrate N. They are growing extremely well. Quite fast but still compact and with good spination. Mammillaria bertoltdii, leuthyi and hermosana have all flowered in their second year. Ariocarpus seedlings also growing fast (for arios). That's the kind of result I'm looking for! They obviously like the ammonium. I would be reluctant to change without a good reason. The osmocote also has much more Mo - 100ppm compared to your practically nothing. Mo is essential if plants are to convert nitrate in their tissues to usable ammonium. You might want give them a boost of Mo a couple of times a year. You should be able to get sodium or ammonium molybdate on ebay. When you use no soil or humus at all in your mix, you cannot leave out a single nutrient and you need to work out the best concentration. That is easy with fast growers like tomato but almost impossible with slow growing plants like cacti and that's another good reason to include some actual soil. Using some soil and/or compost (not sterile peat) in the mix will take the worry out of proper nutrition.
- "The osmocote also has much more Mo - 100ppm compared to your practically nothing." I'm assuming that Mike's Osmocote starts out with 100 ppm Mo before he puts it into his pots.
- His cactus growing season lasts an even 6 months.
- He waters his cacti twice a month.
While I do like his idea about giving my cacti a small Mo boost twice a year, hydroponic growing requires a steady supply of all nutrients with each watering. If I can get a more accurate ppm number for the Mo, I have absolutely no problem adding it to the fertilizer routine with the right stock solution and the right amount of it going into a watering solution.
By the way, and in case you were wondering...
From Promix (https://www.pthorticulture.com/en/train ... t-culture/):
- "Molybdenum toxicity is very rare and, in some crops, the tissue can have several thousand ppm and still not show symptoms. In a few rare cases there has been report golden yellow appearance of the leaves."
From Gardening Know How (https://www.gardeningknowhow.com/garden ... bdenum.htm):
- "Plants can tolerate very high levels of molybdenum but do poorly with little to none of the element."
- "Plants like cruciforms and legumes need higher amounts of the mineral."