In general, the deeper the openers operate, the wider the tilled strip should be. Thus a flat coulter may be adequate for shallow-seeded forages, especially if the coulter and the opener are mounted on the same linkage for constant alignment. A flat coulter can be sharpened. Coulters should be at least 14 inches in diameter to work well in heavy trash. Eighteen-inch coulters seem to work well in a variety of conditions.
Large coulters can operate deeper without pushing residue ahead instead of cutting through.
The coulters usually are operated at about the same depth or slightly deeper than the seed openers. Seed placement depth may be more consistent if the coulter is operated at the same depth or slightly shallower than the coulter, and the seed may be placed in firm soil. Openers are usually double-disk units with disks from 14 to 18 inches in diameter. Double-disk openers are well suited to shallow planting since they can be fitted with depth bands. Small disks require less downward force for penetration.