There are two instances when you should clip/brush hog your pastures....... Well, maybe a 3rd, but if you clip regularly for either or both of the first two, the 3rd won't ever be a factor.
I posted about the first one with
@GreyGus in 'Mowing Pastures' yesterday. The first reason to mow/clip your pastures and the timing on it (and many producers cut too late to be effective) is to remove the seedheads on grasses. TO BE FULLY EFFECTIVE, this must be done at or just before the 'dough/soft dough' stage of seedhead formation. The intent of doing it at this point in time is to remove as many seedheads as possible BEFORE the seeds in the seedheads trigger a hormonal response in the plant that tells the plant to slow its growth because it (the plant) has met its yearly goal which is to produce seed. Mowing once at this point in time should remove at least 80% of the seedheads for the season and will more than likely remove better than 90% of the seedheads. Removal of even 80% is enough to maintain the pastures in a growing (vegetative) state for a considerably longer period of time than if seedheads had been allowed to form. Seedheads can be mowed later to prevent pinkeye/eye damage, but seeds have developed at that point and grass growth impacted in a way grass/forage farmers (you) typically don't want. So mow earlier and accomplish both goals.
The 2nd occasion to mow your field is immediately AFTER the animals are moved off the field and 'weeds' will be going to seed very soon. Mowing at this point in time allows livestock to take full advantage of standing forage prior to mowing and the high protein content weeds that they do eat (not all weeds) without cutting any grass and 'wasting' it. Mowing at this time (the weeds) does a couple things. Removes the seedheads prior to seed formation, and also 'levels the playing field' by setting weeds to the same height as the grazed grass and thus eliminating any ungrazed size advantage the unpalatable weeds may have during grass regrowth. This is particularly important for cool season grasses in late summer that are sod formers just prior to the early fall/late season 'greenup' period after the summer slump.
The third occasion, and not likely to be utilized where the first two are used but much more likely to be used in the west where the first 2 reasons/times aren't utilized, is when/where there is brush removal required. The timing of this application isn't near as important than the first two reasons, unless you are in the west. In that case, particularly if you are planning on implementing a seeding immediately after the brush control, do NOT mow the undesirable brush after it has produced seed for that year and then proceed to drill and/or till the ground when planting your planned forages as that will effectively plant thousands of seeds of the undesirable brush. I was in a class while a MS student at Oregon State University when the field trip took us to a BLM planting that had failed. We listened to the employee who did the planting explain the preparation and seeding and 'in spite of' all the efforts the BLM made, the seeding was overrun with new brush growth within 5 years of the planting. The BLM couldn't figure out why all the brush came back up. I asked, in front of the group of trainees (which I was one), and my tactfulness has improved since then, "When did you brush hog the sagebrush?" The BLM employee answered "mid-late October, and then drilled the grass seed" I replied/asked, in front of everyone there, "Didn't that effectively plant thousands of sagebrush seed?" (The answer was yes as the sagebrush went to seed a couple months earlier.) I got a scowl and what amounted to a stutter of a response back. A learning point for everyone, (including myself about tactfulness) about timing ('
timing' in more ways than one)
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