Comfrey

I grow mine under the hedge but not too far under, and you'll need to trim the hedge so you can get at it     Put it near your compost bins then you can rip leaves off and bung in the bins as a compost activator.
Comfrey has lots of uses.   I don't know about cutting!  I'd dig up the plant and slice a piece off with root attached, and then plant that on your lotty. If the lotties are genuinely abandoned I'd take the lot. If not, replant the comfrey properly after you've borrowed a bit