The time of year is upon us when your turf starts to take on a brownish cast due to seed head production. The driving purpose of most plants is to perpetuate their species by reproduction and each year, grasses will attempt to put out a seed head for just that purpose.
Why does turf look so brown and straw-like during seed head production? Because the plant is reallocating resources toward reproduction and taking a large majority of the carbohydrates normally put toward shoot and root growth away. Also, seed head stalks have a completely different texture than the leaf blades you normally mow, which is what results in that straw-like, brownish-tan appearance.
In the upper midwest, we are already mostly past the time for Kentucky bluegrass to produce seed heads, but the ryegrass period is upon us now in most areas or just around the corner. Perennial ryegrass has much thicker seed head stalks and therefore, will look even rougher after mowing than does Kentucky bluegrass. If you want to minimize this appearance in your turf, it’s important to stay on top of your mowing regimen and not allow the plant to fully ‘go to seed,’ which will result in an even rougher appearance. But, you can never fully keep the grass plant from trying to produce a seed head… Or can you?
I was out at the Iowa State University Horticulture Research station meeting with Dan Strey, the turfgrass research superintendent, the other day and he pointed out one of my old research projects to me where two different levels of fertility were applied in strips for at least 4 years. The two rates of nitrogen making up these strips had always looked different with regard to color, but now there is a distinct difference in seed head production. One strip was full of seed heads as you would normally expect, while the other had virtually no seed heads in it. My memory indicated that the higher fertility level were the strips that had no seed heads in them and I confirmed it after getting back to the office and looking at the old plot plan. Take a look at this photograph:
The whitish looking strip on the left is full of seed heads and received 0.5 lbs of N per month during the growing season for a total of 3.5 lbs N per year. The greener looking strip received 1.0 lbs of N per month during the growing season for a total of 7.0 lbs N per year. The other interesting thing to note is that urea was the source of nitrogen and it has been over a year since these applications were made, yet the differences are still drastic. Normally urea is thought of as a ‘flash in the pan’ type fertilizer, but there a few studies I did at Iowa State that showed it to be much longer lasting than previously thought, especially when the bank of nitrogen was built up over the course of a year or more.
The reason the seed head production was lower with the higher rate of nitrogen is that when nitrogen is supplied in excess, the plant allocates the nitrogen into shoot growth (and some root growth) and delays maturation of the plant. Essentially, the additional nitrogen keeps the plant doing what it would do at a juvenile stage while working its way up to reproduction. Obviously, the cost of applying this much nitrogen and the potential leaching of it into groundwater isn’t enough to offset dealing with seed heads in your turf, but I just found it interesting that it is possible to delay certain physiological events in the plant’s life by modifying the amount of nitrogen it receives. With all that said, the plant will eventually make its way to reproduction, so don’t get any ideas about totally doing away with seed head production. I will have Dan continue to monitor the situation and report back when the higher nitrogen areas start to produce seed heads.