I think some plants need more than what is in the water. If you are giving tap water and you still have black spots then they need it. When they get it, you will notice a change in the plant.
I agree that at least for my cattleyas, they seem to need added calcium. I used to have a problem with a lot of new growths turning black until I started supplementing with a cal/mag solution added to my fertilizer water.
I agree that at least for my cattleyas, they seem to need added calcium. I used to have a problem with a lot of new growths turning black until I started supplementing with a cal/mag solution added to my fertilizer water.
Yep, catts are the worst followed by a few vanda types.
The calcium in eggshells is more soluble in acids. Throw some vinegar in the boiling water, and you'll end up with water-soluble calcium acetate. Of course, vinegar is a herbicide, so one needs to be careful.
Solubility is not necessarily a "yes or no" thing - it's a matter of degree. The more acidic the substrate, the more soluble the calcium will become.
Well my egg shells are finely ground and I put them on almost all my plants. I never get black spots any more so I guess I will keep doing it. Maybe it's like a very slow release or it just makes me feel better