A lot of people have the impression that there is a magic ingredient in chrysanthemum growing called ‘stopping’, which is simply pinching out the growing point to make the plant produce side shoots, and that it is impossible to grow good flowers without knowing the secret. This is just not true.
Most earlies flower best in the first week of September and most lates in the first week of November, and since an early takes about 16 weeks to flower after stopping this is normally carried out in the first week of May.
Lates are usually stopped early June they take slightly longer to flower as the nights start to become colder. There are exceptions to this rule, and many varieties "break" naturally and need no stopping at all, but you will soon learn what works for you, for different varieties.