Forget-me-nots (Myosotis sylvatica) is not usually considered a weed, but it appears as such when it reseeds and sprouts in your lawn. Commonly grown in garden borders and woodland gardens, forget-me-nots is a clumping perennial or biennial that blooms with small clusters of blue or purple flowers in spring. It thrives in U.S. Department of Agriculture plant hardiness zones 3 through 9. After flowering, the flowers drop seeds that can make their way from their original planting site to your lawn. Fortunately, you can kill and control forget-me-nots without exposing your family to dangerous herbicide chemicals.
Dig up large clumps of forget-me-nots in the lawn to remove as much of the roots as possible. Forget-me-nots can spread up to 1 foot wide, so use a round pointed shovel for digging. It's OK to leave the flowers in the lawn if you want to enjoy the flowers while in bloom, but dig them up immediately following the end of the blooming period to prevent them from reseeding in the lawn. Fill in the bare spot with clean topsoil, and reseed with the same grass species in the rest of the lawn.
Pull up young, small forget-me-not plants by hand as soon as you notice them. Pull slowly and carefully to remove as much of the root as you can. Dig around the base of the plant lightly with a garden trowel, if needed, to loosen the roots from the soil. This might take some persistence over the summer and extending into the following spring as seeds that have already dropped in the soil germinate and sprout new plants.
Shake the soil away from the roots of the forget-me-not plants that you pulled up or dug out of the ground. Lay the plants in full sun for a day or two to dry them out and completely kill them so they don't take root elsewhere. Dispose of the dead plant material in a compost pile or green materials waste bin.
Over-seed the lawn with new grass seed so the grass grows thick and eliminates any open space where forget-me-nots can grow. Over-seeding is simply broadcasting grass seed over existing grass. The seeds fall into the small spaces between grass blades and results in a dense lawn.