Last year I planted cosmos and they grew and bloomed amazingly! Just a few days ago I was cleaning out my garden and I decided to completely chop back the old dead-looking cosmo plant. It was completely dried our although it looked like it was really rooted. Did I make a mistake? Do Cosmos come back from the old plant or do they just reseed themselves? I am in Toronto, Canada. I am almost positive that the cosmos I've seen just reseed and come right back. Will my cosmo come back?