A lot of folks like to use common blue violets (Viola papilionacea) in their landscape. However, when they seed themselves into the lawn they become pesky weeds that are very tough to get rid of. Digging works, but only if you are willing to dig deep, wide margins around and under the plant. The entire fleshy rhizome must be removed intact. Leave behind the smallest bit and the violet re-grows.
In addition to flower seeds and rhizomes, these plants also are spread by means of cleistogamous flowers, which are self-pollinating, unopened, underground flowers. If you leave some of these pesky "c-flowers" behind more violets will inevitably spring up.
It's enough to make you nuts. Some folks double dose on herbicides, thinking more is better, but that doesn't work either and often it burns the grass. Granular weed and feeds don't kill violets either. In fact, they aren't a very effective means of ridding lawns of small-leafed weeds because to do the job the herbicide granules must stay in contact with the leaves for 24 to 48 hours.
So I wasn't surprised when my friend called the other day in a dither, wondering if she had to resort to dynamite to rid her lawn of violets.
Consumers can use an herbicide such as Trimec that contains a combination of 2.4-D. MCPA and dicamba. When buying an herbicide check the label to make sure violets are listed. If they aren't, it probably won't kill them.
The other secrets to success, besides choosing the right herbicide, are timing and patience. The best time to treat violets and other perennial weeds is mid-September to mid-October. The weeds must be actively growing in order for the herbicide to work. In hot, dry weather they slow their growth, so putting the herbicide on now is a waste of time and money. In fall the weeds again kick into high gear in order to store carbohydrates to keep them going through the winter. That's the time to launch the attack.
Because the herbicide needs to stay in contact with the leaves for 24 to 48 hours, don't apply it if rain is forecast and turn off the automatic sprinkler system for a couple of days. Remember, too, that broad-spectrum herbicides can damage and kill perennials, trees and shrubs, so take care not to let the spray to drift onto plants you want to keep. Unless your lawn is really peppered with violets or other weedy pests, consider spot treating just the violets. You may not see significant die back of the violets right away. Chances are you will need to repeat the application in two to four weeks. Timing varies according to the product, so follow the label. If in doubt call the number shown on the label instructions. If the violets show up again in mid-May, they will be considerably weakened. Just when the violets begin to bloom is the time to reapply the herbicide.
If you grow violets in the landscape, here are a couple of techniques to help keep them from invading the lawn: If you mow the violets, hose off the underside of the lawn mower deck before and after mowing. This will help keep them from spreading to the turf. Keeping the grass to a minimum height of 2 to 3 inches keeps weed seeds shaded and prevents them from sprouting.
Years ago I planted an area with periwinkle (vinca minor) that was dug from a friend's large shade garden. Early the following spring I was thrilled when a bunch of tiny violets appeared in the ground cover, because these harbingers of spring were the first to green up and bloom and they reminded me of the woodlands where I played as a child.
But soon it became apparent that, left to their own devices, the violets would quickly take over. To keep them under control, I pulled them out by hand and disposed of the them in the trash. Of course I never got all the rhizomes and those pesky underground ''c-flowers'' remained in the soil, so the violets always returned with a lovely show of flowers every spring. My yearly efforts keep them from taking over worked and as long as I kept pulling the violets in June and the bed edged with a spade, they never invaded the adjacent lawn.
