Yellow leaves and stems on your sprouts indicate they’re not getting enough light. Keep them near the appropriate light source and give them as much as they need (they require longer exposure to fluorescence than they do to natural light sources).

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. 

Glyphosate and other non-selective herbicides can kill orchard grass, but they will also kill the surrounding plants. Also, not all areas allow the use of glyphosate due to its environmental impact—which the EPA describes as a "potential risk to terrestrial and aquatic plants and birds, and low toxicity to honeybees." Consider mechanical removal to target the plants specifically.

You should add 1 to 4 inches of mulch, depending on your garden type and needs. Keep in mind that no amount of mulch can completely prevent weeds, but a heavier coverage (closer to 4 inches) can suppress weeds enough that you are only seeing them sprout every few weeks. Finer mulch prevents weeds more effectively than large mulch, so if you’re using mulched leaves or shredded bark, 1 to 2 inches will likely suffice, while 3 to 4 inches is best for larger mulch, like bark chips or straw.