Feeding the grass and controlling weeds are two components of homeowner strategy for having a great looking lawn. Dandelions may be pretty yellow flowers, but they can easily take over an entire lawn. These plants have long tap roots that make pulling them up or digging them out almost impossible. The key is to use a weed killer that enters through the leaves and circulates through the entire plant to the root. Application of a combination product to kill weeds and fertilize the lawn results in grass that is thick, dense, and healthy. Here are some recommendations for using combination products for the best results.