Fertilizer and weeds at Park Grass
Frank Rossi and I wrote this article about the Park Grass experiment.
This experiment has been ongoing since 1856. It involves fertilizer treatments applied to grassland and the many measurements that have been made over the years on the experimental plots. One of these measurements is the botanical composition of the plots, and the results are amazing.
 includes photos of the striking differences between the plots, with those differences is species composition caused simply by the types of fertilizers that were applied.](/post/fertilizer-and-weeds-at-park-grass/featured_hu7eadc1f85a575ab4728e14df4b6c36fe_564090_8d880ee71ef65527bfa70271d6c7240a.webp)
When nitrogen in the form of ammonium sulfate is applied as the only fertilizer, finer grasses predominate and weeds are not present. When potassium is applied, dandelions and other weeds proliferate. Lime also causes an increase in weedy species.
The recommendations for complete fertilizers along with lime treatments that are commonly made for cool-season lawns and other general turf areas are probably contributing to an increase in weed abundance as well. Is it possible that less fertilizer could also lead to less weeds and less herbicide use? That is certainly something to consider, and Dr. Rossi and I suggest that the results of the Park Grass experiment are worthy of further attention from turfgrass managers.