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SET GOALS: If your goal is to remove grass seed heads to promote forage regrowth, then mowing in June is a great option, but one mowing in June is a poor choice for reducing weeds.

When should we mow pastures?

Buckeye Beef Brief: Late arriving spring brought many challenges around farms.

By Chris Penrose

The spring of 2018 was the latest I can remember feeding hay to cattle, and many producers were searching at the last minute to find some extra hay. Pastures were very slow growing this spring until it finally warmed up in early May. On my farm, common orchardgrass typically starts heading out in late April, and it was two weeks later this year. The late-arriving spring brought many challenges around farms, and the rush to get crops in the ground and to make hay has put mowing pastures on the backburner. However, now may be a great time to mow pastures.

Our perennial grasses go through two stages during the growing season: the reproductive stage and the vegetative stage. When grass starts growing in the spring, its main objective is to reproduce, resulting in a seed head. The net movement of energy is up. Once it has produced a seed head, it will transition from the reproductive stage to the vegetative stage, and hopefully the net movement of energy will be down. At that point, the plant wants to store enough energy in the roots or base of the plant to survive through the winter. It is at that point of transition when it is a great time to mow pastures. Once the plant has set a seed head, the quality of the grass, especially the stem and seed head, is low. Removing the stem and seed head will even stimulate new growth. At this point, new growth will be leaves, which will be high in quality for livestock, and the leaves will capture sunlight and provide energy for the plant. While grass has been headed out for a while, mowing pastures soon to remove seed heads is a great option if needed in our pastures.

We need to keep in mind the three big grazing principles to make pasture management successful: avoiding seed heads, residual management, and rest periods. I have started to cover the first principle, but as I transition to residual management, cutting height can play a big role with how close animals will graze and what type of forage will be favored. I have consistently noticed over the years that after I mow a pasture, especially with a sickle bar mower, my cattle will readily graze the new growth. But grazing intensity will slow if they need to graze into the previously mowed stubble, especially in pastures with thick stemmed grass like fescue and orchardgrass. We have some ability to influence how close cattle graze. In addition, cutting height can influence what type of grass will grow. For example, orchardgrass stores its energy in the base of the plant above ground. If we mow or graze too close, we may eventually kill off that plant and possibly favor growth of fescue, bluegrass and weeds. If we graze or mow higher, we favor orchardgrass growth and allow all the grasses to continue leaf development without the roots ceasing growth to produce new leaves.

Finally, it is critical to give the plants a chance to rest after being mowed or grazed. This will allow the plants to store energy in the roots or base as the leaves grow.

Now that we have addressed the needs of the grasses, how about our other problem with pastures: weeds. My colleagues Mark Landefeld, Ted Wiseman and Jeff McCutcheon are in the fourth year of trying to determine when is the best time to mow pastures to control weeds. We have research plots at the Eastern Agricultural Research Station near Caldwell, Ohio, that are mowed at different times. Some plots get mowed one time a year in June, July, August or September; some plots all four times (each month); the control plots (not at all); and we have plots that are mowed in June and August; or July and September. The results of the 2017 study suggests that mowing in June and August works as good as mowing every month to control weeds, and the June mowing will remove the seed heads. With the late start of the season we have had this year, this strategy may be an option depending on your weed pressure.

For many of us, we are lucky if we’re able to mow pastures once a year, but consider what the needs and priorities are for your pastures. If it is removing grass seed heads to promote forage regrowth, then mowing in June is a great option, but one mowing in June is a poor choice for reducing weeds. If perennial weeds are a problem, consider mowing them just before their seed heads become viable. Plot data appears to show that it is best if you can mow twice — once to remove seed heads, and then again to suppress persistent weed problems like the June and August option.

With all of the other activities we have to accomplish on our farms, sometimes mowing pastures falls down on the list of things to do. If you can evaluate the needs such as seed head removal and weed control, maybe we can better time our pasture mowings. 

Penrose is the Ohio State University Extension Educator in Morgan County and a member of the OSU Extension Beef Team. The Beef Team publishes the weekly Ohio BEEF Cattle letter which can be received via email or found at their website beef.osu.edu.

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