ohugal wrote: ↑Sun Sep 17, 2023 9:17 am
As always, I follow these topics with great interest. I wonder if we could establish some guidelines?
As I understood it, in the last watering(s) of the growing season you leave out any fertilizer and focus on (adding) calcium to strenghten the cell walls. But not magnesium, correct? Because magnesium aids in chlorophyll production.
I can imagine substrate composition is an important factor. If you have limestone in your mix, watering with rain water is probably enough to dissolve the calcium and make it available to the plant.
But what if you're growing in 60% pumice and 40% DG/quartz grit mix? Do we then water with acidified tap water to provide calcium?
I grow in 50% pumice, 40% quartz grit and 10% loam (high in clay, not in sand). So, I would probably be good with watering with rain water to dissolve the calcium present in the clay?
Ilvin, do you know what type of soil the plant is in? What type soil do you repot your other cacti into?
You're touching on a couple of important points, so here's the first...
This is something I posted on Mrs. Green's "Astrophytum help needed" thread on the Cultivation forum:
viewtopic.php?p=402602#p402602
The only difference between the hard spring water Mrs. Green uses to water her cacti and the hard tap water I use to water mine is the presence of calcium bicarbonate in the tap water. Calcium is the hardness and bicarbonate is the alkalinity. If growers water their cacti with tap water, the plants are getting plenty of calcium
and magnesium in the water itself, so I'll be in good shape when I give my cacti their last deep watering of the year with acidified tap water and no fertilizers. "So, I would probably be good with watering with rain water to dissolve the calcium present in the clay?" Unfortunately I can't give you an answer because I don't know if the calcium would be available to your plants. When in doubt, I think you'll be better off with tap water. If you're acidifying, great.
Acidic potting media do the job of at least partially neutralizing bicarbonate alkalinity, so acidification may not be required at all. If the mix itself has a pH of 5.5-6.0, then no. If it has a pH between 6.5 and 7.0, a small amount of acidification may be needed unless the fertilizer lowers the tap water's pH -- this depends on the fert.
And now for point #2...
MikeInOz wrote: ↑Fri Sep 15, 2023 6:49 amOne more thing, Ferrocacti seem to like a rather poor soil. That is - mainly mineral. Yours looks a bit too rich in organics.
Completely agree. Looking at Ilvin's photos, it appears that the organic material is chipped/composted tree bark of some sort. It means that his mix is on the acidic side, so adding an acidifier to his water won't be a good idea. But he's also using the wrong mix for North American cacti like his Ferocactus. My recommendation -- a mix of 4 parts mineral gravel (pumice or perlite) and 1 part organics.
Ilvin, mixing 50/50 tap and rainwater isn't the best way to go -- choose one or the other. If you choose rainwater, your cacti will need a calcium source. Some species use limestone, others use gypsum, and Mike is the go-to guy on knowing what needs what. I don't have his level of expertise, so I supplement my fertilizers with a nitrogen-free CalMag supplement. Find out if you can get one -- nitrogen-free is important because your plants will be getting their N from your fertilizer.
If you choose tap water, your cacti will get their Ca and Mg right from the source. But you'll also be dealing with the bicarbonate problem. When you lean out your mix with a higher amount of mineral, that's also the time when you'll need to know its pH so you can figure out the right amount of acidifier (5% white vinegar or citric acid) you should add to your tap water. Here are the steps:
- First -- if you don't already have one, buy a digital pen-style pH meter for testing the water. They're not that expensive. Avoid pH meters you can't calibrate. Meters with 1-point calibration are good, meters with 2-point calibration are even better because they're more accurate. Be sure to follow the manufacturer's instructions.
- Test your tap water and write down its pH.
- Take a clean glass jar and fill it partway up with your mix of choice. Fill the jar all the way up with tap water, put a lid on it, and let it sit for a few hours. Test the the water in your jar and write down its pH -- this is to see if the water reacts to the mix. If the pH is the same, your mix is pH-neutral. If it's lower, your mix is acidic. If it's higher, your mix is alkaline.
Before we go any further, let me know about which option you choose -- either rainwater or tap water.
