All too often, our mowers are delivered from the dealership set up and ready to go … almost. With a similar tendency, mowers are being used in our fields without us, as the end user, seeing that they are set to perform properly in our hay crops.
I first became aware of this as a young man when Dad bought our first-ever disc mower conditioner. It was delivered, and I had it in the field within the hour – I was so excited to finally try one of these new mowers. No more bent sickles. No more clogged cutter bars.
I was mowing a rye cover crop, and every time I hit a mound of soil or a rock, the cutter bar would launch out of the crop. Bringing it back to Dad at the shop, he saw the issue immediately. The springs had not been adjusted to place the proper downforce on the cutter head.
Proper downforce keeps the mower at the set cutting height while allowing it to “float” over obstructions. Within a few minutes of research for the proper downforce (as I recall, it was 200 pounds) and setting the spring tension on each side of the mower to achieve that downforce, I was in business.
The lesson on my issue with downforce should also prompt us to check and recheck the height at which our mowers are clipping our crops. Especially in the age of disc mowers, many fields are pretty much scalped, not unlike our lawns. While this might help tonnage yields on our fields in the short term, what we may also find is that the health of our hay crops suffers.
Leaving more stubble can increase the recovery time of our hay fields, especially in grass crops. More stubble also serves to lower the ground temperature due to improved shading. Cooler ground also means it will retain water during the warmth of hay-making season.
Cutting height depends on our hay crop species as well. Alfalfa and warm-season grasses will see higher yields and nutrient content by mowing about 2 inches, according to several university studies. Cooler-season grass crops such as orchardgrass, when cut in that same range, will experience significant damage. Stands of orchardgrass can actually be killed out by clipping them too low.
An added benefit of raising our mowing height in many grass crops is a lower incidence of weed invasions due to bare ground. Again, the “mechanics” of this are very simple. Broadleaf weeds have more surface area to capture light and convert it to sugars via photosynthesis. (Remember your old high school biology teacher?) This ability gives weeds a tremendous advantage over grasses when it comes to bouncing back after a cutting, especially if the cutting was so low the grass has little green material left to help it recover.
There are several options to achieving the desired cutting height on your mower. Researchers at the University of Tennessee have done extensive work on adjusting mower heights, especially in switchgrass and other native species. Below are a few of their recommendations.
First, you can use stroke-limiting collars on the lift cylinders. Special note should be made: This method is limited to pull-type mower conditioners where the cutterbar is suspended from the mower frame. Achieving the desired cutting height may be a trial-and-error process to determine the number and thickness of collars required. Special attention should be paid to the diameter of hydraulic cylinder rods when purchasing collars. Collars should fit so that they close completely and snugly around the cylinder rod.
The beauty of using this method could be that adjusting between crops and fields is as simple as adding or removing collars. Again, trial and error will be used to determine how many to use, or not use, to transition between cutting heights.
The second method for achieving greater cutting heights is through the installation of high-clearance skid shoes under all or a portion of the mower cutterbar. Some manufacturers offer high-clearance shoes available as an option through the dealership parts supply.
The third option for achieving higher cutting heights is through the adjustment of existing cutterbar skid shoes. Some manufacturers include adjustments on the standard mower skid shoes that will allow cutting heights greater than 6 inches to be achieved. Consult your owner’s manual to determine if your mower has this capability. For some models of mowers, it may be necessary to purchase spacers to lower existing skid shoes.
When trying to achieve increased cutting height, also consider the cutterbar angle. Consult your owner’s manual to determine the procedure to adjust cutterbar angle. Raising the front of the cutterbar may provide some additional clearance. Note that changing the cutterbar angle may affect the performance of the cutterbar as well as the conditioning system in the case of mower-conditioners.
If installed and adjusted properly, any of the methods described above will provide increased cutting heights without affecting the performance or durability of the mower-conditioner. The increased cutting height will help ensure the longevity and vigor of your grass stand, can help reduce weed encroachment and will not negatively affect harvest yields. 
Andy Overbay holds a Ph.D. in ag education and has more than 40 years of hands-on dairy and farming experience.
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Andy Overbay
- Extension Agent
- Virginia Cooperative Extension
- Email Andy Overbay
