Too much of a good thing? Violets threaten takeover

Q. What's the best way to get rid of a highly invasive stand of common violets? I made the mistake of allowing a few plants to take root, because they are beautiful in the spring, but now they have taken over and are drowning everything else. They are difficult to pull and eradicate due to the underground flowers and seeds, and Extended Roundup doesn't seem to provide any lasting benefits, nor does oxalis killer. In one place, there are only violets, so I am considering spreading a tarp over the fall and winter to cook them out, but what do I do when they are among plants I want to keep such as hosta and daylillies?A. Since the days of antiquity, the fragrance and aura of violets have been revered and associated with romance, fertility and celebrations. During the early 20th century, violets so much symbolized the renewal of spring, that the schoolchildren of Illinois voted the Common Blue violet (Viola sororia), the state flower of Illinois.Although violets are self-sufficient, gardeners hate them because they can be unruly and quickly become uninvited guests in our great swathes of exotic turf. Violets spread in two ways through rhizomes and seeds. Rhizomes are horizontal underground stems that send out roots. Some violets, such as the Common Blue violet, which is probably growing in your yard, seeds readily and develops thick rhizomes, To keep violets from invading lawns, maintain a thick lawn by proper lawn care practices. If violets are threatening a hostile takeover of your yard, you have a lengthy battle ahead of you. Violets are a hard to control perennial with a very dense root system. The easiest and most reliable option is to dig out existing violets. However, you must pull up all the entire roots and stems or the plant will grow back. Violets can also be treated with post-emergence broadleaf herbicides containing triclopyr during mid-spring to early summer and/or mid to late fall. Regardless of the time you apply the herbicide, make sure the weeds are actively growing. Be leery of broadleaf herbicides specifically listing wild violets on their label; they are often ineffective, even with repeat applications.However, you may want to take another look at violets. The variety of violets may be overlooked simply because to many eyes "a violet is a violet." Quite the opposite! There are about 25 native violets in Illinois.Violets also perform a special duty within the ecosystem. They are critical to the life cycle of the fritillary butterfly. The leaves and flowers are the primary food of the orange-and black-striped caterpillars when they begin feeding in the spring. In the fall, when dried up violets may appear dead to the human eye, the female fritillary can smell the dormant roots, and will lay her eggs on or near the violets. The tiny larvae hatch and spend the winter under nearby leaf litter.While violets are fond of shade, they do not desire full shade, but flourish with filtered sunshine. The Downy Yellow violet (Viola pubescens) tolerates part shade, and has a numerous flush of yellow flowers in the spring. It is also well behaved and is not invasive in the garden. The Cream violet (Viola striata) is another good choice. It is a late bloomer; about two weeks later than most violets. The Canada violet (Viola canadensis) is also ideal for gardens since it does not spread aggressively, can tolerate some sun, and is one of the few natives that possess a slight fragrance.For sunny locations with heavy soil, try the native Prairie violet (Viola pedatifida). The Labrador violet (Viola labradorica) also prefers full sun and is an excellent choice for planting between pavers and steppingstones. The purplish-green foliage maintains its good looks all season long. Whether planted as drifts of blue within a woodland setting, tucked alongside a few spring-flowering bulbs, or even planted in a container where you can control their rampant spreading, violets are a delightful addition to the garden fulfilling a certain promise of spring. bull; Provided by Mary Boldan, Mary Moisand and Donna Siemro, University of Illinois Extension Master Gardeners. Send questions to Ask a Master Gardener, c/o Friendship Park Conservatory, 395 W. Algonquin Road, Des Plaines, IL 60016, (847) 298-3502 or via e-mail to cookcountymg.com@gmail.com.