Chrysanthemums, also called garden mums, are a popular autumn addition to the landscape. Blooms of white, yellow, orange, red or burgundy mix well with pumpkins that decorate our home and front entry. Those potted mums purchased each fall can be planted to grow your own mums that will return year after year.
Why Pinch Back Mums
Mums sprout in early spring and grow in a bush-like fashion. Left un-pruned, the mum plant can develop a gapping center as the weight of the flowers and leaves on the stems causes them to fall over. To prevent that possibility and maintain a compact shape with more branching, the mum should be pinched back, or pruned, starting in early spring and continuing into mid-summer.
When and How to Pinch Back Mums
Pinching back (also called pruning) should first occur in the spring in April or May when the stems of new growth of the mums are about 5 inches tall. With the stem in hand, place your index finger and thumb about 2 inches from the base of the stem and just above a leaf. Use your thumb (nail too if needed) to pluck off the stem just above a leaf. Continue this process for each stem of the plant. As the mum grows and again reaches about 5 inches in height, repeat the pinching back process on each of the stems.
If you want to use this pruning opportunity to collect cuttings for planting, switch to a sharp knife or garden clippers so the stem is not collapsed from the action of pinching. Sterilize the knife or garden clippers first. I keep a small spray bottle of a 50/50 mix of water and bleach to sprits the cutters and then wipe them dry with a paper towel. Follow the same stem removal process but instead of pinching off the stem, clip or cut the stem. Clippers can also be used instead of pinching even if you don’t want to keep the clippings. Collect the longest cuttings for rooting.
Rooting Mum Clippings
Fill a small flower pot or container with all perlite or a 50/50 mixture of perlite and sand. Moisten the contents of the flower pot.
Remove the leaves from the bottom half of the stem. To increase the potential of successful rooting, dip the tip of the stem cutting into rooting hormone up to the first node (where a leaf was removed). Push the stem into the perlite up to the first leaf on the stem.
Place the flower pot in a sunny location and keep the perlite moist. Turn the pot daily for more even sunlight distribution. Roots should form in less than four weeks. If any of the cuttings die, gently pull them from the pot. Give the clippings another month in the perlite pot to grow longer roots before transplanting to a flower pot with potting mix or plant in the ground.
Source: Personal experience backed up by: Iowa State University Extension