Jet washing can wash away weeds without bending or kneeling to pull them. However, the results will likely be fleeting because the weeds will return unless you use a stronger method that takes them out at the root. Use a jet washer for short-term weed removal, but use a stronger method if you want to get rid of weeds for good.

Yes, dandelions are considered perennial, broadleaf weeds.

Yes, Johnsongrass is a hard weed to kill. It has the ability to grow fast and spread even quicker, so it requires a detailed plan and thorough application to eliminate it. The best plan of action is to kill Johnsongrass while the weed is establishing itself by hiring a lawn care professional or following the steps above. 

The hydroseed mix—known as a slurry—helps grass seed take root in many ways. Water combines with the mulch, allowing the grass seed to stay moist while grounded in the soil. The extra fertilizer then provides the boost the seed needs to flourish. In just a few weeks, you'll be ready to break out the lawnmower again.