Planter Opener Blades: 3, 3.5, or 4mm? And Depth of Bevel!

by Matt Hagny, consulting agronomist for no-till systems since ’94.

‘Round and ’round. More choices than ever. I continue to see more aftermarket suppliers and OEMs (Monosem) putting 4mm-thick planter opener disks/blades on the market. A few cautionary notes: As these wear, they can become extremely blunt. Since the double-disc opener design has them exactly side-by-side, this results in trying to push 8mm worth of steel into the soil at the leading edge. The problem is made much worse by some of these 4mm blades having less bevel than what was typical on 3 and 3.5mm blades. In other words, these get very dull very quickly.


While we at Exapta have long advocated 3.5mm blades over the old 3mm, the 4mm is simply going too far and causing problems with row units not being able to penetrate the soil (and not cutting mulch, i.e., hairpinning). We love the 3.5mm over the 3mm because of improved blade rigidity – the 3mm were simply too flexible for no-till, and often resulted in pinched furrows even if the seed-tube guard was full-width. The 3.5mm eliminated most of the problematic flexing of the blade. Granted, a 4mm is even more rigid, but the gains are not enough to be worth the cost of not being able to cut the soil and mulch cover. It’s not so bad when the 4mm blades are new, but as their sharpness diminishes, it gets ugly – and this happens really quickly if the bevel is shallow, such as with the blades on Monosem planters with the ‘French’ row unit (and also some aftermarket companies’ planter blades). [Note: if you need to convert a Monosem planter to use different blades, you’ll need special bolts – give us a call if you need these.]

(Exapta has no dog in this fight: we don’t sell planter opener blades.) 

Planter blades for JD, Kinze, AGCO, and Monosem should be replaced when half the bevel is gone—they’re getting dull. Compare depth of bevel to new blades.

Get your measuring tools out. Success at planting time depends on doing your homework now.