| As far as I know buckwheat doesn't have any incompatibles and should be okay with pretty much anything. It can be grown and a cover crop while adding calcium and will atrract hoverflies. |
Here is a link that might be useful: Source: Companion Planting Guide - ZenfulNeps.com
| Addendum: Little bit more research and found out you probably shouldn't plant buckwheat and legumes together as they will compete against each other for nutrients. |
Here is a link that might be useful: Companion Planting Guide - ZenfulNeps.com