Dandelions are winter perennials that can be spread by seeds and will return from the root or even a piece of the root. In general they are fairly easy to control with a combination of preemergent herbicides and postemergent herbicide applications made before seed dispersal. Before you start mixing your chemical, pick a batch of young dandelion leaves and make yourself a salad. I've been eating them myself ever since I was a little weed puller and they are delicious.