Belgian mums are an exciting new type of chrysanthemum with hundreds more blooms per plant than older mum varieties. Belgians have more flexible stems and are less susceptible to breakage in windy areas. Belgians also have a more rounded shape with flowers covering the entire plant instead of just on the top like many traditional mums. We apply netting or a plastic ring to our mums when they first start to develop flower buds. The mums will continue to grow through this support offering extra insurance against breakage. Unless you want to delay flowering, Belgian mums do not need to be pinched back during the growing season to maintain their naturally shorter, fuller shape.
Plant chrysanthemums in full sun (6+ hours) in well-drained, enriched soil. The planting hole should be at least twice the size of the root ball so the mum can root out easily. Mums profit from winter protection. They are best planted on the east or south sides of a wall or evergreen that will shelter them from winter winds. Don’t cut off the old foliage in fall. The old stems will help protect the root area. Mums have fine, shallow root systems and are prone to winter ‘heaving’ caused by freezing/thawing cycles. Adding extra mulch after Thanksgiving by way of evergreen boughs, chopped oak leaves or a bark product will provide additional protection. Be sure to remove the extra layer of mulch around March 15 before the mums start to send up new shoots. Ideally, mums should be planted at least 5 weeks before a killing frost in order for them to become established.
Every 3rd or 4th spring, divide chrysanthemums to rejuvenate them. When the new growth is 1’’ to 2” high, dig up the root ball. Replant the younger more vigorous growth from around the perimeter of the clump and discard the older central growth. Fertilize twice per month through July using a water soluble fertilizer such as Jack’s Classic All Purpose 20-20-20. You can also use a balanced slow-release fertilizer that should be applied just once in May.
Pinching traditional chrysanthemum plants yields compact, bushy plants with more blooms. “Pinching” simply means to remove the tips of new growth stimulating the chrysanthemums to send out side shoots. Start in the spring (around May 15) when the new growth has reached 8-10″, cut these shoots in half. When new side shoots have reached 8-10”, pinch these in half (around June 15). You can make one last pinch around July 4 if you want your mums to bloom as late as possible, but do not pinch after July 4 or bud formation won’t occur soon enough to ensure flowering.