Yes, dandelions are considered perennial, broadleaf weeds.

Herbicides containing a combination of the active chemical ingredients dicamba, fluroxpyr, and quinclorac are most effective at purging your turf of white clover. However, for small home lawns, organic prevention and control can be very effective methods for killing clover weeds and save you from using harmful pesticides that might damage your lawn.

Johnsongrass and crabgrass are invasive weeds that can overtake your lawn. Crabgrass is a low-growing grass most often seen in lawns, flower beds, and vegetable gardens. While you may find Johnsongrass growing in your lawn, it will also grow in pastures, crop fields, and the edge of the road. Johnsongrass is much coarser than crabgrass. If left alone, Johnsongrass can grow up to 8 feet tall. 

Yes. One of the main benefits of organic mulch is weed prevention. Organic mulch forms a physical barrier that blocks light and stops weeds from germinating. It can reduce your need to weed and improve the physical appearance of your garden.