I planted one packet of Cosmos sulphureus (Sulphur Cosmos, Yellow Cosmos) several years ago and not had to buy more seeds since. They show up all over the yard every year now. Up until this year they have been under 3 feet tall and spindly looking...like they are supposed to be. These three plants got bushier and bushier as the summer progressed, even the leaves are much larger than the regular plants. I am certainly going to collect seeds from these, the tallest one is well over 5 feet tall...you can see the flower up near the top of the photo. This patch also contains about 8 of the smaller versions. It's so large I can hardly walk down the path between them and the Golden Rod on the other side. 3 large Cosmos ( photo / image / picture from toni's Garden )
To show the size difference in a new light.....both leaves were taken from bottom of their respective plants and cut off at the main stem. The large one is 15" (38 centimeters) long and the small one is 6" (15 centimeters) long. Cosmos leaves ( photo / image / picture from toni's Garden )
My orange and yellow cosmos never grew that big... and I do love the color of the blooms, but I didn't like the foliage as much as I did their pink, red & white cousins. So... I cleared them out of that bed. Now... I'm thinking I should have saved some seeds and spread them around here and there. Guess I'll be watching the seed racks come spring time. And dang-it Toni... one day I'm not going to let you "force" me into growing something (yeah right).