My friend Andrew Wille sent this article about using comfrey as a fertilizer. It is loaded with Vitamin B-12 — no wonder it grows fast — so at the very least comfrey fertilizer would give other plants an instant energy boost. If this works, it would be worth growing comfrey and fighting it back, simply to feed the garden. (Like raising your own livestock for the manure, but easier.)
This reminded me quite suddenly — I’d completely forgotten — that my mother kept an antique teapot with a tight lid in the kitchen, which she filled with water and where she dumped egg shells. The sulphur smell when you opened the cover could have knocked the devil out of the room, but covered there was no hint of Evil Fragrance.
When the pot was full, she took it outside to water her plants, then crushed the egg shells underfoot and sprinkled the shards around the base of certain ones like peonies or clematis that seemed particularly to thrive on that calcium. No need to purchase commercial bonemeal.