Corn planting depth

April 7, 2016 8:58 PM
Blog Post

I've had a lot of questions/discussions this week about planting corn. I had some growers get started Monday, some others were going to start towards the middle or tail end of this week, a few were going to wait until Monday, and a few were undecided. When to start planting was probably worthy of a blog, but that horse has sailed out of the barn in my part of Iowa.

The good news is that our soil temps are around 50°F, the planting zone of most of our soils (SW/WC IA anyway) are amazing so far this spring, the NH3 is about done and the moisture forecast is looking perfect for planting! But… temperatures look pretty stagnant for the next week, so as the old saying goes, “store your seed in a cool, dry place” is what we are doing for the next week or so anyway on planted acres.

With our spring fever, growers are asking about planting strategies and the cold soils (bouncing around 48-50°F as of Thursday 4/7 in my part of IA). I have had a few asking about “can we plant a little closer to 1.5 inches or less to get this corn out of the ground faster since it may be cold?” In my very humble opinion, but based on years of digging up corn planted from 1-5 inches deep, targeting 1.5 inches is not my preference.

So how deep to plant?
Some agronomists say 2 to 3 inches and some say 1.5 to 2 inches. Me, I say target 2 inches at this point in time. So, as you get off the planter to check seed spacing and depth, take a good read on where it is at and make sure it is at least 1.75 inches, and remember that rain may (and probably will since every field I have been in has been in great “fluffy” shape in the planting zone) settle the soil around the seed zone and shallow up the planting a little—so plan your depth accordingly. This is especially relevant if you happen to run your trash whippers more aggressively. Disc openers tend to work better around the 2” target in my experience, too.

Target 2.5 inches if the soils get really dry. Planting “too deep” (2.5-3 inches) isn’t typically as problematic as too shallow, but I have seen some loss of stand, vigor, and uneven emergence from 3 inches planted corn in cool, wet soils- occasionally. However, I see many more season-long issues with shallow planted corn than deep planted corn. 

Planting too shallow?
Yes, this leads to big problems such as rootless corn, sidewall compaction, poor root development, increased seed/root system mass in the herbicide zone, poor seed zone closing, the shallow seed zone can dry out, and no doubt I am forgetting some other potential problems, but you see where I am going with this. Err on the side of “too deep” rather than too shallow.  

Licht and I worked with on this article a season or two ago, it shares a little more detail if needed;


Clarke McGrath On-Farm Research and Extension Coordinator - Iowa Soybean Research Center

Clarke McGrath currently serves as the On-Farm Research and Extension Coordinator.

Prior to joining Iowa State University, McGrath spent nearly a decade as a retail agronomist and manager in the GROWMARK system, earni...