Ever wonder why those beautiful, dense and compact garden mums you purchased at your local nursery and planted in fall grow more leggy in your garden the following year?
There's a reason.
Left to grow naturally in the garden, many varieties of garden mums will grow tall and become leggy by summer. Sometimes they even start to produce flowers, which you don't want to let them do. Why? Because, the flowers of garden mums, Chrysanthemum morifolium, prefer life on the cool side. If you allow your garden mums to bloom during the summer chances are the flowers will quickly fade and turn brown from the heat. This is because they prefer cooler temperatures, and will hold their flowers for much longer (30 to 60 days) during the cooler temperatures in fall. This is why some gardeners call them "fall garden mums."
So, what to do? Just some simple, timely, pinching and the mums in your garden will be just as full and compact through the season and bloom just as heavy as they were when you bought them at the local nursery and garden center.
Pruning Instructions
Mums sprout in early spring and then start to grow in a bush-like fashion, sometimes. But, depending on weather and the environment, if left to grow naturally without any pinching, some varieties will start blooming too early and grow quite tall and leggy. When this happens the weight of the flowers on the stems will often cause the branches to fall over. To prevent this from happening, and to maintain a compact shape with more branching, you can pinch mums back starting in early spring and continuing into mid-summer. Where I garden in central Georgia, I usually cease pruning around July 4th, partly because that's an easy date to remember.
This being said, you don't have to pinch or prune mums at all. If you choose not to prune you might only get a short bloom period in summer, and it might be necessary to use plant supports to keep leggy stems from flopping over throughout the season.
If you choose to pinch your mums, below are some helpful tips. This pinching process may seem drastic, but the results will be bushy, well-shaped fall-flowering plants.
First Pinching: Start pinching stems in spring when the plants have reached a height of about 6 inches in length. To pinch them back, grab a stem between your thumb and index finger about 2 to 3 inches above the base of the plant, and just above a leaf, and simply pinch it off. If you're like me, and keep your fingernails clipped short, you can use a pair of sharp pruners or snips to cut the stems.
Second Pinching: After the first pinching, new stems will emerge from just beneath where you initially pinched the plants. When these new stems have reached 6 inches in length pinch them back by about 2 to 3 inches just above a leaf. Continue this process for each stem of the plant.
Thereafter: You can repeat this process until mid-July at which time you can cease pruning and allow the plant to grow and produce buds that will bloom in fall. Pinching back any later than mid-July can reduce the number of flower buds.
NOTE: If you're reading this article and it's already June or early July and you have done no pruning, and your mums are tall and leggy, you can simply cut the plants about one-third to half way back. This should help to create a more dense plant that will bloom in fall.
After the Fall Bloom
After your mums have finished blooming in the fall, and the foliage has gone completely dormant, you can cut the dead stems back to just above the ground. That being said, northern gardeners can leave the dead stems there to help insulate the roots from severe cold weather during winter.
No matter what region you garden in, for winter, it's a good idea to apply a 2-inch layer of pine straw or shredded wood mulch around the roots of your mums. If you place mulch directly on top of the plant make sure to remove it in late winter or early spring so that the new growth can emerge in spring without being damaged.