When you are trying to grow a prize chrysanthemum, size is going to matter. In order to make it physically possible for your chrysanthemum to create a mammoth flower, you will have to help it focus and conserve its resources by judicious "pinching" of inferior buds and flowers. Pinching is a form of pruning performed by using the thumb and forefinger to remove the growing tip of a plant. This results in a shorter plant with fewer flowers and larger blooms. However, pinching must be applied strategically in order to succeed in this endeavour. You must take proper care to only pinch the correct parts of the plant at the proper times in order to grow mammoth chrysanthemums.
Pinch the growing tip of the chrysanthemum when the plant is about six inches tall. This will encourage the plant to branch, giving you more options to choose from when it comes to the perfect stem for your chrysanthemum. Small branches will soon begin to develop as the plant learns it can no longer grow up.
Break off all but three of these branches. These branches will be the main branches that you will use to grow your show blooms.
Remove all flower buds not on the top three inches of each branch. You can do this with small clippers or by breaking or pinching them off by hand. This will enable your plant to dedicate the majority of its energy to developing a relatively small number of flowers.
Examine the top bud. This bud is called the crown bud, and as soon as you are sure it is healthy, you should remove all the other flowers on the stem. A healthy crown bud will be fat, green and show no discolouration or evidence of insect or bacterial damage.
Continue to remove small side branches as they develop. This will focus all flowering resources on those three main flowers. Your plant will appear a little bare, but the flowers it bears will be truly magnificent.
Chrysanthemums thrive on organic fertilisers. If you are trying to grow vibrant, enormous blooms then be sure to fertilise with natural plant food. Make sure that your mums are not too crowded or their flowers may be smaller and less colourful.