Ok I can't use gypsum from old wall board to lower my soil pH because it contains toxic glue residues. Where can I get some inexpensive garden-safe gypsum in bulk and in my area which is SE SC?
You should be able to find 50 lb bags of gypsum in farm supply stores.
The real question is: DO YOU REALLY NEED GYPSUM?
Many people think they need gypsum and they don't. I personally don't like gypsum. I use other products to get the same results.
Gypsum is calcium sulfate. It is mainly used on slightly alkaline soils (pH > 7) to maintain calcium and sulfur levels in the soil. It is also a great soil conditioner. If you got a soil pH < 7, you definitely don't need gypsum. You need lime [calcium carbonate).
However, for clay soils you will be better off using tons of compost and other organic matter instead of gypsum for aerating and loosening up the clay soil.
I love using aged or composted sawdust from my horse manure barns in my soil to get the soil conditioning effect. Wood products are excellent for clay soils, and much cheaper than gypsum.
If you use compost all year round, cover crops whenever you can, and lots of organic mulches all the time, your soil pH will be buffered by the organic matter, and you will be able to grow anything no matter what your native soil pH is. (NOTE: any soil pH from 6.5 to 7.5 just needs compost no lime or no sulfur products!)
The humic acids in compost react with the natural acids and bases in the native soil of your garden beds, and return a near neural soil pH effect that tricks your plants so that they get all the soil soluble nutrients that they need when they need it.
If I need extra calcium in my acidic clay soil, I get it from dolomitic limestone or from my composted horse manure or from my cattle feed soil amendments that I use.
If I need extra sulfur for some plants, I use Epsom salt (magnesium sulfate) or add some apple cider vinegar into my special compost tea recipes.
I agree with the captain. A pH of 7 is neutral and just fine for growing a wide variety of crops and ornamentals. Compost helps to neutralize the pH of soil as well as improve drainage and provide nutrients and you can usually make it or get it for free.
If you really must lower your pH to grow something that needs acidic soil, try pine needles and coffee grounds. (I know there was a post that said used coffee grounds were neutral, but it can't hurt just in case.) I really don't think gypsum will acidify your soil, it just neutralizes it.
