If you dont do the MFR-approach (that sucker only puts beans on the north side) like I did, you can arrange the logs in a 4/5 ratio. To avoid stray beans, there must be at least one block above the logs (better two). Just put the logs in the following order (x are logs, o are beans):
The pattern is repeated by using the bottom and right log as the left and top log for the next element (as a knight moves).
That way you have four beans per five blocks space (same pattern goes well with sugar canes).