Very carefully. You should be cautious when using any of the above methods, as any one of them could lead to you accidentally killing desired grasses and plants. However, there are selective herbicides that can target certain plants over others. Look for a product that only affects the type of weeds you want to eliminate and spares the plants you want to keep.

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. 

Weed control applications usually cost around $100 each for a standard-size yard, and most professionals charge between $30 and $60 per hour for manual weed removal. Your total is affected most by the size of the weeded area. Some weed service companies offer weed control treatments, selective herbicide spraying, and manual removal and upkeep as part of a package, costing around $600 annually. You might pay less if you hire the same company for other lawn services, like flower bed upkeep, aeration, overseeding, and pesticide application.

The fastest ways to kill weeds and unwanted grass include burning them, pouring boiling water on them, or pulling them out by hand, as these methods work almost instantaneously. For a quick-acting solution that works within a few hours, you can use a commercial-grade herbicide like glyphosate or a DIY vinegar, salt, and dish soap mixture. While effective, be aware that commercial herbicides introduce chemicals into your lawn. The slowest method for killing weeds is to starve them of sunlight and nutrients using mulch or fabric covers.