It’s also good for deep planters when you don’t really need that much room for the roots of your annual plants. You save on money (much less potting soil is required) and weight.
I don't have peanuts but I do have large pieces of packing foam since we live in the middle of nowhere and have to have things shipped if they're not locally available. Poking holes in that stuff would work, too, I imagine. However, we have no shortage of rocks, lol!