Q: What do I use to kill the weeds in my lawn without stressing the grass? What fertilizer should I use and how often?
—Jennifer, Dayton, Ohio
A: Roger Cook replies: There are several products that will kill weeds without stressing the lawn. You should go to your local garden center and ask for their recommendation. If possible, tell them exactly what kind of weeds you have in your lawn. There are weed killers used on walks, patios, driveways, and bed areas that will kill grass as well, so make sure they understand what you are trying to do. When treating weeds in a lawn I like to spot spray. This allows me to only treat the areas that need it, using the least amount of herbicide. On large areas you will probably need to use a granular herbicide peat with a spreader. Be careful to follow all directions on the bag. To stop the lawn from stressing out, make sure it is well watered before any herbicide application.
Here in New England I fertilize four times a year: April/May, mid-June, early September, and early November. In the April and November applications, I use a high-phosphorous fertilizer. (The phosphorous content is indicated by the middle number in the formula). This may be labeled as a starter or fall fertilizer. In June and September, I use a fertilizer higher in nitrogen (indicated by the first number in the formula), because nitrogen promotes top growth.