What concerning lawn clippings as fertilizer? According to Washington State College agronomists, yard trimmings may average 1% to 2% nitrogen, 0.03% to 0.06% phosphorus, 1.3% to 2.3% potassium as well as some micronutrient. At best, this would certainly amount to a 2-1-2 plant food. It is a mix of natural as well as ammonium nitrogen, rapid as well as slow-moving types. So, compared to an industrial organic fertilizer such as Organic Garden-tone plant food (3-4-4), it is fairly low in nutrients. Nevertheless, it does add some, and most importantly, it is totally free.