I plant Cosmos every year in my garden. I start them by seeds. I buy the seeds, I save the seeds. In summary, I've tried lots of ways to grow the seed. I can tell you: they are very easy to grow! In particular, the
Cosmos Sensation. I've tried others too. Some worked, some did not.
The Sensation Cosmos I grow every year, no matter what. They are reliable. I barely stick the seed to the soil. I keep the seeds wet - not soaking wet though - as that makes them grow faster. Plant them when they are around 5 inches tall. I make sure I protect the seedling from slugs and snails. The slugs-snails love when the Cosmos is young!
This year I tried
Cosmos Psyche White. I loved the white flowers with the different petals. They grew very well from seeds. I planted them the same way I plant the cosmos seeds. However, they were gone much faster than the Sensation flowers.
I tried
Cosmos Cosmic Orange last year. I think I only saved 3-4 plants from all the seedlings. I did not try again this year, as I tried not to grow too many orange-yellow flowers this year.
Several years ago I tried
Cosmos Pied Piper. They did grow, but the amount of flowers was not as much as the Sensation.
The only problem with Cosmos is that it takes work for you to get flowers the whole summer. You need to cut the flowers that are done so the plant does not set seeds. If the plant set seeds, you will have less and less flowers. So, it will require you to go to the garden and do some cleaning. For me, it is usually not a problem: it does not take long to remove the dead flowers.
In summary, if you want a flower to start from seeds that is easy to grow, give Cosmos a try.
Luiza