It won’t be as good for a soaking liquid. It is still acidic, but does lack the beneficial bacteria to help ferment whatever it is you are soaking. Whey that has been heated is certainly good in a garden, especially around the tomatoes which love calcium. Other uses are to make a marinade for meat, or put in smoothies (there is still loads of minerals). Sometimes I throw it in with broth.

The other thing you can do is make Ricotta from the whey Traditional ricotta comes from “twice cooked” milk. Though whether it will work or not depends on teh method you are using to make your cottage cheese. Here’s a recipe for how to make Ricotta cheese from leftover whey. It will explain to you the two types of whey and you can then determine if yours will work for Ricotta. It doesn’t make much, but it’s something. There will still even be leftover whey from making Ricotta, and it can be put in the garden at that point.