Alternatively it is possible to leave the shoots on the old plant and re-plant everything in the spring. Plants created from newly rooted growth tend to be more vigorous than those left on the old plant and they will almost always be a replica of the original. Follow the 'Getting started' link for more information. Blooms are normally cut 24 to 48 hours before the show date and kept in relatively deep water to allow the stems and petals to charge themselves up. If I had a large number of blooms for a Saturday Show I would perhaps make a start on Wednesday evening, but no sooner.
Chrysanthemums are vigorous plants with active root systems.
As the plants grow during summertime the increase in number of leaves and total leaf area mean that moisture loss through the leaves can be considerable. When blooms are forming and petals elongate it is the moisture taken in by the roots that plays a big part in influencing individual petal size and ultimately, overall bloom size. Of course, cultural technique and previous treatment in terms of feeding and climate conditions will also play a part in determining bloom size and quality. So, the answer is yes, adequate moisture at the roots is required. Chrysanthemums will not grow too well when kept in shady conditions.