With our planter series complete, there yet remains much to be said about planting. So today, we alight on a related topic and another favorite of mine: planting depth.
What is optimal? That is the question.
Optimal, in terms of planting depth, means balanced. The optimal depth for a seed is a depth that balances stability and time to emergence. Seeds planted too shallow don’t experience optimal stability: their soil bed is subject to sometimes wild environmental changes and with little soil left atop to cover their nodal roots, which set up a full ¾ inches above the seed, they are at risk of developing dreaded floppy corn syndrome. Seeds planted too deep simply waste valuable time toiling through the soil before they break the surface.
There is a school of thought out there that adds moisture into the equation, which dictates that planting depth should vary across fields and time. I’m going to cast my vote against this as a variable planting depth makes consistent emergence—which leads to stand consistency which leads to ear consistency which leads to higher yields—difficult to achieve.
Going forward with our two factors—stability and time to emergence—in mind we can determine a set optimal depth that will strike a healthy balance between the two, and in doing so, help you achieve the consistency that best supports high yields. That depth, my friends, is 2 to 2 ½ inches.
Yikes, I hear some of you saying. That’s deep! And yeah, it kind of is, especially if you’re used to planting at 1 ¾. Adding that extra ¼ to ¾ inches will definitely increase your time to emergence, by about 48 hours, but it is totally worth it since optimal time to emergence doesn’t necessarily mean quickest time to emergence, especially if achieving a quicker time causes an imbalance with our other critical factor, stability.
The stability of soil conditions increases considerably beginning at about 2 ¼ inches under the surface. Soil shallower than this is subject to hourly environmental changes—the temperature of the soil can fluctuate greatly due to sun penetration and air content in the soil. Such fluctuation can not only disrupt the germination of a single seed but can also cause inconsistent germination between seeds since soil in different locations in your fields will not fluctuate evenly.
Seeds planted at 2 ¼ inches deep aren’t subject to such fluctuations as the soil above insulates it and protects it from flagrant temperature variations. And the stability of your soil at 2 ¼ inches carries across your fields, meaning that the cozy bed of a seed in Location A matches the environment of the cozy bed of a seed in Location B. With such stability, germination is rarely disrupted and is regular across the vastness of your farm.
If you’re still a little dubious about this depth, let me point out that I am not alone in embracing it. Research by Pioneer Hybrids shows that planting at the 2-2 ½ depth accounts for a 5-9 bushel per acre increase in yield. The depth eliminates runts and minimizes the cost of planter errors like skips and doubles. Overall, the 2-2 ½ inch depth encourages maximum stand consistency which, as I mentioned above, leads to maximum ear consistency, which, if you’ve read this article lately, is the main factor in increased yields.
An important addendum to this entire conversation is this: though planting at the 2-2 ½ inch depth eliminates much of the variability in soil conditions, it isn’t a license to plant on the wrong side of a warming/cooling trend. Planting deeper does give you a little cheat room, but there is too much at stake to become lax about your attention to soil temperature. You want to plant into soil that measures at least 50 degrees 2 inches below the surface and you want to plant when the three-day temperature outlook will either keep the soil at this temperature or above. You can predict soil temperature by adding the high and low for a given day and dividing by two. If any of the three days following planting provides an answer to that equation that is less than 50, then friend, please reevaluate your planting date.
In the end, successful planting is truly all about providing stability for your precious seeds. We can go overboard in this concern (yes, it is physically possible to plant too deep), which is why considering time to emergence provides an essential balance, but we should always be very mindful of it as we make decisions. As advances enable us to increase our plant populations, we increase too our investment in our choices. We’re putting a lot on the line in our fields. There is much potential out there and a proper planting depth is key to unlocking it