Looks like a variety of agapanthus.

I think the common name is Spanish bluebells. Don't let them go to seed or you'll have plants everywhere.

I think the plant is a wood hyacinth. The blossom is not in a ball at the top of the stem like agapanthus. Both are so pretty. I hope to find both in a local nursery. If not I will try mail order. The wood hyacinth blooms in spring but the agapanthus is a summer bloomer.

Toby, I will keep that in mind. Although I have at least one spot that would be nice full of bluebells.

They are so prolific, just find someone with them growing in their yard and I'll bet you could get some bulbs from them. Or ask on Next Door or Craigslist. I think people are happy to share plants like this that are so easy to grow and spread with abandon.

Where are these located?

I've been digging mine up where I don't want them. I have pink and blue. I'm happy with just a few here and there.

Agapanthus is a much larger plant although there are dwarf varieties. They're very common in California.

I like the wood anemone a. nemerosa robininsoniana as a spreader with spring blooms. They go dormant in mid summer when it gets too hot but bluebell foliage doesn't even last that long.

My first thought was agapanthus. It would be very helpful to know the geographic location. I have this in my front and back yard, although I did not plant them myself - the plants will grow here wherever you happen to drop them - you do not need to dig a hole for the roots - they will find their way into the ground. They will grow in partial shade as well as full sun here. I have not photographed mine, but they have leaves that look pretty much your photo.

I have a ton of these and didn't know what they were, they are blooming right now and I am in NE Ohio. Looks like Gardengal has the right answer.

I am drooling over the pink spent blooms that are scattered over the area!! What are they???

Lars, the flower head of Agapanthus is very different from those in the picture....other than the color.

arcy, I betcha it's Azalea blooms.

The spent flowers are camellia blossoms.

If you post plant ID questions like this in the Name That Plant forum, you can be guaranteed of a correct ID, not just gesses. But I can assure you that both of mine are correct :-)

And the wood hyacinths are considered little more than weeds here in the PNW. No one plants them intentionally - they just pop up from seed or from squirrels from other areas of the garden or from neighbors and once present, almost impossible to get rid of or predict where they might appear next season.