Weed killer?

I agree with the rest. A long time ago I worked a summer for a horticulturist/landscaper. The two things I recall from that job is how to mix a Harvey Wallbanger and never ever use weed killer, weed & feed etc.
Not 100% sure he was right but my sister's neighbor used weed & feed one year on his lawn and volunteered to treat my sister's yard. It was never the same after that.