Hi-Yield Weed & Feed Lawn Food Is Our Best Selling Combination Fertilizer And Weed Killer. Fertilizer in Weed & Feed has a 15-5-10 balance, part fast acting ammoniacal nitrogen and part slow release urea nitrogen. Weed Killer in Weed & Feed is a Trimec Complex, killing a wide variety of weeds found in the common home lawn. In the MidWest apply around May, when dandilions are in full bloom. Apply when the grass is wet from dew, rain or sprinkling. Do not allow any watering or rain for 24 hours so the weeds soak up the trimec. If you have very tough weeds like creeping charlie and violets, you will need to spot treat with Weed Out about a week after your Weed & Feed Application. Weed & Feed may also be applied in the fall, if you have had weeds sprout up over the summer. One 18 Lb. bag covers about 5,000 sq. ft., an average lawn. This is a very popular and effective product.