@GardenOfHerbs, It's actually very fun experiment to mix them in a glass and see the gypsum forms in front of your eyes, but I bet the plants don't think it's useful :D By the way if you do want to mix them and they are still available to plant, calcium carbonate is an option too.
Some people also use water that had egg shells sitting in it for a while, but with that I have no experience.
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