As we worked in a client's garden this week, a neighbor popped over to ask: These violets in the lawn. Is there some kind of medicine we can use to get rid of them? No matter what we do they keep coming back!
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You can dig them out or kill violets with a weed killer. If you choose to use herbicide, do it early in the growing season. Use a broad leaf weed killer that lists violets on its label (at this writing, that's products containing trichlopyr, or the combination of herbicides called Trimec) or a non-selective herbicide that does not preclude follow-up planting or seeding (active ingredient glyphosate as in Roundup products). Understand that the broad leaf weed killer will probably be only partially successful and glyphosate will kill both weeds and grass.
However, killing the plants currently bugging you is not even half the battle. Those violets got in because the lawn was weak so there were open spaces where seeds could sprout, yet you've done nothing to improve the lawn's density and thereby break the weed cycle.
Above: Common blue violet (Viola sororia, a.k.a. V. papilionacea) is native all over eastern North America, adapting well to most open areas in sun or shade. Look- alike marsh blue violet (Viola cucullata) is a lover of damp places that's also native to eastern North America. These aren't the only two violet species but these two alone are capable and ready to occupy any mowed place where lawn grass has open spaces because of shade, compaction or dampness.
Where turf is thick and tall, most weeds have a tough time getting started or spreading. So whenever you address a weedy lawn, determine the environmental condition that's limiting the turf's growth and correct it. Aerate to loosen compaction, prune overhanging limbs to increase sunlight or switch to more shade tolerant grass seed, mow higher so grass blades can cast the shade that inhibits weed seed germination, then water and fertilize more regularly.
In fall, violets may be most susceptible to broad leaf weed killer (chemicals that don't kill lawn), although you probably won't see the results until spring. In spring, you may have more success with a non-selective herbicide (glyphosate).
Below, left: Most violets form a starch-rich crown, like a mini-iris. Pull off only the top or leave even a piece of the crown, and the plant's only diminished, not gone. Better to insert a fork, loosen the area and then pull. Then the soil has been aerated as well as weeded.
Above, right: Weeds had no trouble sprouting in the small gaps between grass plants in this weak lawn. Now there is a big bare spot created by killing or digging a violet, and the soil there is loaded with violet seeds. Unless you make this whole area more agreeable to bluegrass or fescue, and then cover it with grass seed, your weed killing will only net you a new crop of violets.
Below: Violets are particularly sneaky weeds. In spring you probably recognize that they have just bloomed, have seed pods, and know not to leave the plants lying around to drop those seeds. In fall, these cunning plants develop "closed flowers" -- blooms that never open but do produce seeds. See the pods at ground level, and the developing seed within? Don't leave those laying about, either!
I hate it when they kill the violets.
- Virginia Smith -
Gardening Law #10: A weed is simply a plant growing where you don't want it. Corollary 10A: Even the finest garden plant is a weed if it puts itself where it's not wanted!
Corollary 10B: If you want it, it's not a weed!
Right: Well into her 8th decade of gardening, our mentor Virginia Smith endorsed this, saying:
"Lower your standards. Don't be such a perfectionist. There are places where what we cultivate are weeds, and vice versa. Dandelions are very pretty. I'm not going to worry about that creeping buttercup. I realized I've been fighting that weed for something like 50 years and recently I realized it's very pretty.
I hate it when they kill the violets in my lawn with the stuff they put on. I love them... the flower, the leaf. They're very pretty."