Scrutable

You used to be able to buy copper ammonium sulfate to put on your seedling compost to protect against "damping off", a very common fungus that destroys young seedlings in the moist atmosphere of a covered seed tray.

But you can't buy it any more. You can still buy copper sulfate. But copper sulfate on its own is rather acidic. It burns leaves if you spray it on plants that are leafed out, as I have discovered by foolishly doing that once. Hence I assume the reason copper ammonium sulfate was used.

I had the idea of putting a little bicarb in the copper sulfate to neutralise it. That unsurprisingly precipitated copper oxide, but as a fine suspension. I tried spreading that on my seed tray. It worked so well as a fungicide that 10 days later my seed tray has numerous little mushrooms growing out of it, which I've never seen before. Though mostly the seedlings are looking healthy. I think I need something that keeps the copper in solution.

I was thinking I couldn't buy ammonia, as I haven't seen it for sale on shelf at the hardware store for many decades. But checking it out, I realise actually I can. So I can make my own copper ammonium sulfate.

But any other ideas for making a less acidic solution of copper ions out of my copper sulfate, perhaps using some household substance I might have to hand?

Close with the bicarb. Try heating it first to drive off CO2 and thereby convert it to quicklime. https://en.wikipedia.org/wiki/Bordeaux_mixture

shpalman wrote: Fri Feb 21, 2025 11:55 am Close with the bicarb. Try heating it first to drive off CO2 and thereby convert it to quicklime. https://en.wikipedia.org/wiki/Bordeaux_mixture

In fact I have lime to make Bordeaux mixture, which I spray on my vines. But it appears to be a suspension. It is inclined to block the sprayer. So I don't think the copper will get down into the potting mix if I give it a topical spray of Bordeaux mix. Copper stops the fungus spores from germinating, it doesn't kill them once germinated. So that's why I think I need it in solution, to get down into the soil, and kill spores not only on the surface, but underneath the surface too.

By random chance I found myself sitting next to an academic chemist yesterday. She was playing the chamber organ, but drinking from a periodic table mug, so I asked...

So even adding ammonia to copper sulfate isn't straightforward. It will initially act just like any base and precipitate out copper oxide. But adding more ammonia will promote dissolution by chelating the copper with ammonia ligands, to make something like Cu(NH3)4SO4. This should be a very dark blue/purple colour. So this makes me wonder if my copper ammonium sulphate I used to buy was actually that, because it was very dark blue/purple, rather than the royal blue of copper sulphate.

Of course I can buy ammonium sulphate fertiliser, I now realise. And dissolving copper sulphate and ammonium sulphate in solution is the real way of making copper ammonium sulphate, if that's really what I want. Actually get the correct ratio of copper to sulfate ions. But I've just googled a picture of copper ammonium sulphate, and it is on the pale side of royal blue, not at all dark blue. So I guess what I was buying was incompetently named. And it probably was the ammonium chelated copper.

She was unable to think of any other household base I might have or easily buy that I might mix with copper sulfate and keep it in solution.

And I now realise that by mixing bicarb with copper sulfate I was making Bordeaux mix. Because the CO2 rapidly fizzed off.

One of my seed species has given me only one surviving seedling, which is not enough as it requires multiple for cross-pollination, at least 3 for safety. Fortunately I kept some seeds back of that one, and can try again. It's all possible some of the seeds I planted didn't germinate and will still germinate and survive, now I have taken the seed tray out of the propagator. But didn't really need sowing this early, March will be good enough for my tomatillos.

You could try this (p61): https://library.sciencemadness.org/libr ... ed1937.pdf