The willowleaf sunflower (Helianthus salicifolius ) is perennial. It is not very demanding as far as soil is concerned, but it requires full sun. It can vary in size a great deal and spreads by creeping rhizomes, covering quite a bit of ground over time.
I first saw it growing wild on the embankment of an abandoned railroad in southern Ontario. As it is native to Wisconsin and New York states, I expect it is also native to Ontario, but it could have been brought in. Although it was growing in gravel, that railroad embankment was surrounded by deep, rich soil, and the plants stood as tall as traditional annual sunflowers, much taller than myself.
I planted a small clump of it here at Roche Fleurie in the Bruce Peninsula where it grows in just a few inches of top soil and a few inches of subsoil on top of the bedrock. It survived and has even spread, but the tallest flowering stems are only about four feet tall instead of eight.
I started with just a small clump by the pile of stones on the left in the picture above. That was at least fifteen years ago. Now the patch of willowleaf sunflowers covers an area of about twenty by ten feet! It is slowly spreading out, overcoming all the grasses and other plants in its way as you can see in the picture below. To my knowledge it has never self seeded.
It is very attractive with only one bloom at the end of each stem. It blooms very late, that is to say in October. It is ideal for a "wild" garden. It does spread, but not very fast and could be easily controlled if necessary. It suffers from no insects or diseases and holds itself quite well, even in a strong wind. It also works well as a cut flower.
Since it does so well, I thought I would also try a close relation, the Maximilian sunflower (Helianthus maximiliani), another perennial eastern North American native. The leaves are narrower and sage green, the flower disk is more yellow. They also grow rather short here, about three feet tall. I started them from seed, and the seedlings were also put it in full sun in a meadow. They grew well, but the plants are not as vigorous as those of willowleaf sunflower. They probably resent the lean diet of poor soil or the length of winters. However, they are only in their second year. They might get better established in time as they also spread by rhizomes just like the yellowleaf sunflower.