I have found that Brushwood Nursery delivers large, husky clematis far superior to other websites.
Last year I ordered some varieties from Donohue's that have yet to flower. Brushwood Nursery has clematis that bloom the first year! AND, I have found little individual tags in the plants that say Donohue's on them! Brushwood must keep them a year before selling them. I think that this greatly improves your chances of sucess. I have never lost a clematis from Brushwood. I know that they sell only healthy plants.
Their prices are extremely fair, and the shipping charges are a great deal. Far below what other sites may charge. An extra incentive is added if you order more plants.
The only drawback is that you had better order quickly before your choices are all sold out. Then you'll have to go on a waiting list, (which I have done ) to be notified by email when more come in.
I just love Brushwood Nursery and have had extremely good luck.
I was disappointed last year with Donohue's. (Spring 2009) The plants delivered, which Brushwood did not carry, were small and half the size of my plants from Brushwood. I learned my lesson. Never again.
I just can't say enough good things about Brushwood Nursery. Try them. You won't be disappointed!