The seed must be fresh and fertile. Where is your source for seed? If it is from one plant by itself it may not form fertile seed without another genetic individual of the same species nearby. I suspect many plants in this country are clones of the same individual anyway!

I have found that the best way to propagate G. manicata from my own plant at home is to physically separate the small "baby" plants that the mother plant produces each year. I'll dig up roughly a 5-gallon bucket sized start, containing one or more healthy looking leaves, a cone and good amount of pink hairs, making sure to keep the latter two moist, but not the leaves. A deep enough hole and enough water (and a few kind words) usually results in a successful transplant, in my experience.