6 Plants You Should Never Cut Back in December, According to Horticulturists

Lilacs

Lilacs put on a beautiful show when the weather warms, but pruning them in December will reduce the likelihood of flowers. "[They] bloom on old wood," says Linda Langelo, a horticulture specialist at Colorado State University. "December pruning removes flower buds for next spring."

December pruning also makes lilac shrubs more susceptible to cold damage and diseases, she says. So when should you trim them? "There are different species, so figure out when yours will bloom, and prune after they bloom," she says. "Think about when the shrub is actively growing. The pruning cuts will heal over faster, and the new growth will be healthier."

Mock Orange

Cutting back mock orange is a bad idea for a few reasons. "Pruning in December removes next season's blossoms," says Langelo. "[Also], if you prune before it goes into dormancy, you increase stress on the shrub. It loses energy and will be slower to leaf out."

Instead, prune mock orange after it blooms in the spring. Make sure to dead branches, crossing branches, or branches that show signs of disease.

Azaleas

Azaleas add a beautiful splash of color to your garden in the spring—but leave them alone when the temperatures dip. "Pruning in December will remove spring buds and decrease blooms," says garden coach Teri Speight.

Instead, cut back your azaleas after they bloom—Speight recommends no more than six weeks. "Prune them to manage form and size," says Damon Abdi, assistant professor of landscape horticulture at Louisiana State University. "This shapes the plant, while allowing ample flower buds to form."

Maple Tree

Maple trees should be pruned in mid-summer, so trimming the branches in winter is the wrong timing entirely.

"They bleed heavily when pruned in December," says Langelo. "The sap attracts other insects, and it stresses the tree. The pruning cuts that are open also allow fungal spores to enter easily."

If you need to, wait until January. The freezing and thawing cycles will be reduced, she says, slowing the sap.

Hellebores

 Hellebores can liven up a winter garden, but it's best to wait a bit longer into the season before picking up the pruning shears. Cutting back in December risks "damaging the buds," says Speight—she recommends waiting until late winter or early spring, when new growth has sufficiently emerged.

"I've found that removing leaves in late spring also provides protection to the hellebore babies that surround the plant," she adds. 

Camellias

Winter is when camellias are in full bloom, so it makes sense that you should maintain them in December. However, pruning now can have some negative side effects. "You cut off the bloom right at its peak, or prevent later winter blooms from being in full display," says Abdi.

Instead, he recommends pruning in spring. This will give the flowers plenty of time to prepare for winter.