No yellowing. Especially if it is applied with chelated micronutrients and the 1/4 lb or less of N Syngenta tells you to use. I get 30 days out of it. Lawns do get really tight and thick on it. The green color is intensified as well. But I do only use it when needed. That thickening of the lawn is something I watch. Too thick and it is time for a dethatch.