The center of the flower may turn brown if it has been affected by a blight disease. Fungi will cause brown spots to appear on the leaves, which may eventually cover the entire surface of the leaf. In some cases, the chrysanthemum may suffer from a combination of these symptoms.
In a pot, a chrysanthemum plant lasts for a few weeks inside. Keep it in a brightly lit position and water when dry. Pick off any dead flowers or discolored leaves. When flowering has finished, take it outside, cut it back to 15cm and plant it out in your garden.