Before we do anything, there are a few matters to discuss.
jerrytheplater wrote: ↑Sat Aug 12, 2023 8:39 pmNot knowing how much fertilizer is in John Innes fertilizer is a problem. All we are doing is guessing. My guess: they are not using any slow release fertilizer that will last for years.
I think you could be onto something -- from Gardeners' World, this is an example of what one of the John Innes composts looks like:
- 2048x1365-Platycodon-SEO-LI3172849-c9aabdb.jpg (95.31 KiB) Viewed 4041 times
I don't see any slow-release fert granules there, so if the John Innes 2 contains a low-level fertilizer that won't last long, Hero878 can speed up the process by flushing his pots with distilled water and nothing more:
- Saturate the mix until water comes out the drain hole like a faucet.
- Wait for an hour, and flush again.
- Wait for another hour, and flush for the 3rd time.
When the mix dries out completely from the top to the bottom of the pot, this will give the roots of his cacti a "clean slate" with no fertilizer left in the JI 2, at which point he can fertilize per my recommendations. Unfortunately it'll be too late in the growing season to expect much of an improvement yet, but at least it'll give him a good head start on next year's growing season. And he might be pleasantly surprised -- I sure was when I started supplementing my Dyna-Gro 7-7-7 with potassium sulfate in August 2020. At the end of that summer, the improvements were small but quite noticeable on a good number of my cacti.
jerrytheplater wrote: ↑Sat Aug 12, 2023 8:39 pmDaveW could shed some light on John Innes composts.
Good idea -- since he lives in the UK and he's been growing cacti for a long time, I'll send him a PM and ask him to review "the facts of the case" here. If he's familiar enough to know the JI 2, he can tell us whether or not it contains a low-level fert that is leached out easily by flushing. I'm pretty sure that it is, but it would be nice to get confirmation. The flushing I just mentioned is Plan A. In case there's a good reason for
not flushing Hero878's pots, this is Plan B:
jerrytheplater wrote: ↑Sat Aug 12, 2023 8:39 pmIf all Hero878 can get is John Innes compost, I'd say use it with caution and maybe use half strength custom fertilizer solutions for the initial few fertilizings. Watch the plants to see how they react.
Hero878 wrote: ↑Sat Aug 12, 2023 9:44 pmI bought some Epsom salts today. Will get some Ca next.? Not sure about how well fertilised the soil is but it shouldn't last long hopefully.
First of all -- if you wouldn't mind waiting a little bit, you'll find out whether you should go with plan A or Plan B.
I PM'd our horticulturalist-in-residence MikeInOz with the details regarding the Chempak clematis food, my calculations and dilutions, etc. This is what he had to say:
MikeInOz wrote: ↑Sat Aug 12, 2023 4:37 am
I don't see any problem with that Steve. Especially if his John Innes mix has some loam in it. The JI mixes usually have some dolomite added as well so he probably won't need to worry about added Ca and Mg for 3 years and not at all if his water has it. He can also use Gypsum for the S.
Cheers
Mike
Check your source for JI 2 and find out if it does have some dolomite in the compost you're getting. I've always thought that hard water is bad for cacti (or at least desert cacti), but now I wonder if it's one of those myths people keep falling for. I can see how high mineral content in well water would be a problem, although I think the hardness in your tap water isn't so high and in fact could be an asset. Jerry taught me about the difference between temporary and permanent hardness, so let's break it down:
- Calcium bicarbonate existing in tap water represents temporary hardness. When the water evaporates, we're left with insoluble calcium carbonate which is unavailable to plants. Temporary hardness can be measured with a pH meter -- if you test your tap water and it reads above 7.0, the reading will tell you that you may need to acidify the water. Whether you need to or not depends on a couple of factors, the pH of your potting medium and any affect the fertilizer (plus supplements if required) has on the water's pH. A bit too complicated to get into now, but we can discuss this later if you'd like.
- From LibreTexts Chemistry:
"Hard water is water containing high amounts of mineral ions. The most common ions found in hard water are the metal cations calcium (Ca2+) and magnesium (Mg2+), though iron, aluminum, and manganese may also be found in certain areas. These metals are water soluble, meaning they will dissolve in water. " [My emphasis]
That's permanent hardness which can't be measured with a pH meter. Doesn't matter though, because if your tap water is within acceptable limits, your cacti will be able to get plenty of Ca and Mg from there even if the JI 2 doesn't contain any dolomite. As Mike said, you can add Gypsum to your mix for the S. How much and in what form -- powder or gravel? Unfortunately I can't answer those questions because my cacti get enough sulfur from the ammonium sulfate and potassium sulfate supplementing my General Hydroponics ferts.
If you'd rather not mess around with the possibility that you'll have to acidify your tap water, watering your cacti with rainwater will make things easier for you. Should that be the case, the Cultivers CaO and Epsom salt will be required to supplement the Chempak clematis food.