A number of years ago I was smitten with lily of the valley species that had unusual leaves. This version, with its striped leaves, I foolishly planted in the middle of a garden bed. Every year I would dig out a number of clumps to donate to the Wisconsin Hardy Plant sale in the spring. Last fall I attempted to erradicate them from the bed since it was filled with much less aggressiver perennials.
But I still love the fragrance and the gorgeous leaves. So I culled the plants with the most striping and potted them in a plastic nursery pot, put that inside a bigger plastic container and buried the whole thing up to its rim in a section of the garden that is not yet designed. So it can function as a holding bed as needed. This spring, as soon as I saw the tips of the lilies, I pulled the pot out of the dirt and repotted them in this low container. They bloomed and seem to be growing well. So I am getting to have my cake and eat it, too, at least as far as these lilies are concerned.
The other technique to control the spread is to put lily of the valley in a fairly inhospitable location. This variety has a pale edge and larger leaves. And it comes from one of England's most famous Elizabethan houses, Hardwick Hall. I bought three! I am managing to keep it in check because of its location. It's planted in a bed under a 60-year-old Arborvita and a honey locust tree of the same age. The soil is hard-packed clay.
Hosta 'Golden Tiara' seems to have no problem thriving there and the lilies increase each year but not so fast that I can't dig them out if they start to wander too far.