Hay Mowing Height

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Yellow ruler in green hay field indicating grass is 6 inches tall.

Mowing height of hay plays large role in grass stand health.

It’s that time of year. If you’ve done any riding around, you have seen a ton of hay put on the ground. The 2020 hay year has begun.

Lots of questions come up concerning making hay. So, let’s start at the beginning. How short can you mow the hay? Most of what we have in this neck of the woods is fescue so we’ll focus on that. Most sources indicate leaving 3-5 inches at the minimum. This is so the grass can grow back without having to dip into it’s energy reserves. If the grass is mowed short over and over again, the plant is stressed a little more each time. Add in hot temperatures (they’re coming – it’s only May) and potential drought (we can only hope it won’t be as dry as last year), and those two factors add additional layers of stress to the plant. Stressed plants take longer to begin regrowth, which can lead to more weeds. Also, cutting hay short can expose more soil to the sun which can raise soil temperatures and cause soil moisture loss at a quicker rate.

If you leave a little more height on your fescue when you mow it (or graze it), you will improve the health of the grass and the soil and reduce the presence of weeds, which will lead to a thicker stand of desirable grasses.

But what are you giving up by leaving that 1-2 inches of standing fescue? The rule of thumb is that 1 inch of forage height in the field amounts to 200 pounds of dry matter per acre. Now, hang on, before you go thinking that’s an extra bale for every 4 acres if your bales average 800 pounds. That was 200 pounds of dry matter. If your bales weigh 800 pounds, you probably have approximately 680 pounds of dry matter per bale if your hay is about 15% moisture. So, you may get another bale for every 4.7 acres if you mow an inch shorter. But in five years, what will your grass stand look like because it has been stressed 2-3 times per year for those five years? Leaving a little bit of grass when you mow may save your grass stand down the road.