zpeckler wrote: ↑Fri May 05, 2023 5:11 pm
Thanks for the update on your fertilizer regimen, Steve. Last year I used the All Pro regimen and I got some of the best growth my cacti had in years! I'm doing this updated regimen this year.
Here's a question I've been mulling over for a bit... Using your fertilizer regimen and a mineral mix ((or in my case, a *mostly* mineral mix--100+ degree heat during summer means I need about 25% organic otherwise things dry out too quickly)) do you have an opinion on amending the growing medium with some pelletized dolomitic limestone and gypsum for those species that grow on limestone in habitat?
Before I get to your answer, I just wanted to mention that I gave all of my cacti their first deep watering of the growing season a couple of weeks ago -- pure rainwater and nothing more. Unfortunately things here in SoCal are cooler than I'd like, so I'm not sure if watering this weekend would be a good idea. Next weekend? Definitely yes, and the collection will be getting its first feeding under my new fert regimen. Although I did well with the Dyna Gro All-Pro over the years, I'm looking forward to even better results with the General Hydroponics ferts and supplements.
Adding a small amount of limestone and/or gypsum to your mix is a good idea depending on the species you're growing. I don't only because A. I don't have enough confidence to know that I'm adding the right amount, and B. I found that adding a small amount of CalMag supplement to the watering solution is easier. 1/4 tsp. of TPS CalMag per gallon did wonders last year, so I'll include it when the cacti get their regular feeding this year. If you'd like to go the limestone/gypsum route, MikeInOz is an expert, so this may be helpful -- from "The Cal-Mag of my dreams?" thread:
MikeInOz wrote: ↑Thu Dec 29, 2022 6:19 amA lot of the Texas and Northern Mexico plants grow in soils with both limestone and gypsum so I give them both. Things like arios, epithelanthas, many thelos, all astros, all coryphanthas and escobarias many mamms ( you have to check) pelecyphora, etc. No need to add limestone more than once. Gypsum is much more soluble so I add a bit at the start of each growing season. If you can use particles of gypsum which are say 2 - 3 mm in size they will probably last 2 years or more. Limestone will basically last forever.
All the other things like notos, rebutias, lobivia etc get a little gypsum but no limestone as they like more acid conditions. If you regularly add trace elements (especially if they are chelated ) there is not so much need to worry about the pH. (but I still try to keep it around 5.5 - 6). I have only seen severe chlorosis in 2 cacti. An echinopsis and a Neobuxbaumia. If it gets too bad there is no saving the plant. So most things seem to tolerate a fairly wide range.
With that said, cacti can get calcium from various sources, so IMO the source doesn't matter as long as it's in a form available to the plants. Speaking of...
My ability to store rainwater is limited to 4 1-gallon jugs, and 3 got used up already, so I'll have acidify my tap water during the rest of the growing season. Calcium bicarbonate = temporary hardness in the tap water which can be neutralized by acidification with:
- 5% white vinegar. The byproduct of acidification is calcium acetate in the watering solution.
- While vinegar is fine for small collections, growers with big collections need something more concentrated. If that's the case, I recommend citric acid because it's a lot safer than phosphoric and sulfuric acids for home use. The byproduct of acidification with citric acid is calcium citrate in the watering solution.
Unlike the insoluble calcium carbonate left behind when tap water evaporates, calcium acetate and calcium citrate are highly soluble -- and a good source of calcium available to our plants. Obviously not the main source, but it's a nice little bonus.
P.S. I just saw Jerry's response, and I agree -- stay away from the pelletized limestone.