Violets should stay low enough for mowers to cause little to no damage to the plants. If the lawn is tall fescue (the main type of cool-season lawn grown in Maryland), then it should be mown at about a 3- to 4-inch height as often as needed to avoid having the grass get too tall between mowings. That would mean about once a week during the height of spring and autumn growth, and less often when the grass is more dormant due to winter or summer weather. If the lawn is mown too infrequently and the grass gets much taller than about 5 or so inches between mowings, that can stress the grass by having too much cut off at one time. Lawn weeds like Ground Ivy (Glechoma) tend to have an easier time overwhelming a lawn when the grass is stressed. This weed in particular also tends to thrive in areas that are semi-shaded and/or which stay moist, such as from poor drainage or over-irrigation during dry weather.

Unfortunately, there is no easy control of Glechoma (such as with herbicide) that won't also potentially impact the violets. Manual removal is the only way to selectively remove it (other than by very careful, targeted herbicide spraying), and manual removal typically is not feasible for a large infestation given how hard it can be to remove all pieces of Glechoma so it doesn't regrow.

Miri