I found this forum last fall, and have started applying the lazy principles of mowing high, etc. we have a large backyard that is being overtaken with violet. Granted, the grass back there hasn't benefitted from our new systems much yet, and we did spend a lot of time last year digging up the violet by hand, but it is spreading faster than we can dig it.
Since things are poor back there now, should we till the whole thing, adding topsoil and compost, and then start from scratch with tall fescue? Or will tilling just chop up the violet and make it spread faster?
PS- I know many will ask why not leave it, but we prefer grass for the kids... We are taking about a fourth of the yard and expanding the garden...
They have a waxy coating that would make chemical herbicides (even vinegar?) roll off harmlessly. So don't even try that. They mostly thrive in acid soil with low calcium so adding lime may help slow their spread. The are also edible and you can CANDY them, which the kids may like. There's also a recipe to make lovely violet jelly that is a pale purple color.
Spring and fall are the best times to dig it. Try to go deep to get all the roots. IMHO tilling would and adding compost would just make them come back stronger.
You could try sheet mulching like for a new garden to kill them off, or leave black plastic on them to cook them for a few weeks then re-seed with grass/clover mix.
Grass should choke out violets if it's healthy enough. At least around here, if a person't not careful, grass chokes out everything. Being a little on the lazy side, my first thought would be to figure out what the grass needs to help it along - more sun? Water? Food? After that's figured out, I'd consider over-seeding if there's just not enough of it, or it's the wrong type.
Grass should indeed take over if the soil is right for grass. This is my third year embracing the "organic gardening for the cheap and lazy" article, and the grass is really winning this year. Three years ago, the violet was a close second after Creeping Charlie, with grass a dismal third, just ahead of dandelions. I tried toxic gick, I tried pulling them all, I tried throwing hundreds of dollars of new grass seed on them. I could have kept doing those things for decades.
1) Get a soil test. I had conifers, raspberries, ferns; everything that would point to acid soil. The soil test came back alkaline. The steps I've taken to reduce pH are really favoring the grass.
2) Know that it will work if you do the right things. This is a years-long process. Trying to get instant results is what gets us into these situations in the first place.
3) Get a soil test. Wait, I said that... anyway, do it.
I would vote against overseeding. If the soil is right for grass, you can watch the existing grass take over on a daily basis. if you have some bare/weedy patches, the grass will just take over next year. Bury the weeds in 4 inches of compost and watch what a happens.
IMHO, if you let the grass grow taller the roots will be able to grow deeper and get more nutrients and help it eventually win out. In the photo below I had a weed problem in my pasture (the one on the left) from the grass being kept too short (cattle would graze there several times a day on their way to the waterer at the top of the hill). I fenced it off to let the grass get stronger to choke out the weeds that were taking over. On the right is my neighbor's pasture with too many horses. They keep it grazed down to an inch, letting the weeds flourish, so you can barely tell but the whole thing is lovely with blooming daisies.
The way violets grow, hugging the ground, mowing only eliminates the competition for them but if the grass were taller it would "take" more of the sunlight, letting the grass get stronger than the violets. At least that's the pasture way of looking at grass vs. weeds.