I'm a newbie as well, and my knowledge on this subject is based only on observations of my own Jackmanii. The first year I planted my vine, I only had 4 petal flowers. Now in the vine's 3'rd year, it has produced both 4 petal, and 5 petal flowers ( and it has grown tremendously since it's first year as one scraggly looking vine, each year it comes back MUCH fuller than before. When I first adopted my clematis I thought maybe I would need to buy more than one plant for it to fill out the way I had hoped...ha ha). So, my very unscientific guess would be that age/maturity has a factor in the size of the flower/number of petals.
Heidi
7bDigitalV>I bought a Polish Spirit. The only difference I noted between a