Val, I just got lima bean seed that have the purple slashes on them so I'm sure they have butter beans also.

heirloomseeds.com

bernie

so, i'm one of those apostates who thinks that butter beans are just limas you picked too early...

if you're looking for a great lima, the willow-leaf lima from southern exposure seed exchange is EXCELLENT. very productive.

the cheapest, best cover crop is... i think... black eyed peas from the grocery. just plant 'em, water 'em till they sprout, then till them under (or, as they do in much of the world, just cut them down and use them as a green mulch).

i meant to say... let them grow for however long, THEN till them under. i'm sure there's some rule about optimal size, but really, you're just looking for some organic material and N here, so let them get as big as you want... the nice thing about bep is they are very disease resistant and need little to no extra water. i know a couple local growers who use them...