Does anyone know anything about gardening?

lupins are a nitrogen fixer so you can chop them up and dig them back into the soil

Depending on which variety they are, you may even be able to do something with the seeds:

https://en.wikipedia.org/wiki/Lupin_bean

I've had various lupin burgers and they've all been pretty tasty.

Difficult if you have one of the bitter varieties, which can be fairly toxic (as noted in the article linked to above).