Sweet Violets
I sowed these years ago as an afterthought at the end of summer and forgot about them. They surprised me two years later, when they emerged all at once and since then I had more and more of them every year.
Sweet violets are cold-loving perennials; they grow in dappled tree shade but can tolerate full sun if the weather is not too hot.
Violets propagate by seeds and runners and will spread quickly, covering entire areas if the soil is moist and fertile.
They are eager to naturalize in lawns and can become a problem if you don’t want them there.
The flowers come in every shade of blue and purple, all the way to white, and the plants cross-pollinate to create surprising hybrids.
If you don’t like them spreading into a certain area, you can just dig up their runners, separate them from the mother plants and move them to their desired location.
They will make themselves at home there in no time, although if the ground is fertile, it’s a safe bet their seeds found their way to it already.