We also have a Korean Spice, Juddii and Burkwoodii. But I pruned too late last year so we didn't get too many blooms. Oops. Sino-calycanthus 'Venus' has buds the size of a large grape but it hasn't bloomed yet. Venus is planted in a lot of shade. It's done great but it's later than the others and wants to grow more horizontal than tall. Still, I can't really compare the Venus to the others since it's a different kind of calycanthus.
We have a calycanthus ML on each corner of the front of the house. They are half-way under the eaves of the house so they are about half-dry and half-normal water. One gets a lot more sun than the other. The one with more sun is a visibly larger plant, has bigger leaves and usually more blooms. The flowers on the one with more shade seem to last a bit longer. They seem to like at least a medium amount of water. When they get dry, the leaves get a bit crispy around the edges and their blooming and growing stalls. Still, they seem to take whatever happens to them with a shrug. They're not too fussy.
Due to some gutter issues, two of our calycanthus had the soil washed away from a large portion of their roots (we didn't know it). Just bare roots showing drying and baking in the sun. They didn't leaf out on one side but they didn't die either. Added some peat moss-enriched soil, watered and they leafed out just fine. They like the soil to be a bit acidic or they will get yellowish leaves with green veins. A bit of Epsom salt makes them happy but we don't fertilize much. I've never had to prune them. They make a nice shaped shrub and turn yellow in the autumn.
The first blooms that I photographed from Michael Lindsey this year was 07 April and the first ones on Athens were 15 April. But they'll still be putting out sporadic blooms in Aug/Sept.
