Dandelions are one of the most persistent weeds gardeners face in their quest for the "perfect lawn." Dandelions are the most common type of weed in the United States and Europe, and they are very hard to deal with because they do not die once the growing season is over and quickly reappear the following spring.
Dandelions are green broadleaf weeds that eventually produce a yellow flower. This flower then forms a sphere of white seeds as it matures. These seeds spread throughout your lawn through wind pollination, resulting in multiple patches of dandelions throughout your yard. The roots for these small weeds can be up to three feet deep in the soil and thus, to completely remove this weed from your lawn, you must attack it at the root. Since dandelions grow and flourish in moist soil, they can be an effect of heavy rains or overwatering.
There are a number of products that will remove dandelions from your lawn. These products attack weeds at the root so that they do not resurface again the following year. The Scotts brand of weed control has proven effective for me in the past if I use the weed control as soon as I see the dandelion start to grow. Refer to the product information of your weed control product to see when you should use it. Dandelions can be problematic for many inexperienced gardeners.