Have you ever noticed some trees hang onto their leaves after all the leaves of others have fallen to the ground?

Just like attracting pollinators is the purpose for colorful wildflower petals, there’s a reason why some leaves keep on hanging on all winter.

Marcescence is the term for this winter retention of leaves.

Beech and oak are deciduous native trees, losing their leaves each fall. But young beech, as well as oaks, American hornbeam, and witch hazel hang on to some of their leaves throughout the winter. They are marcescent.

In the fall, trees create a separation zone (abscission layer) between petiole (leaf stem) and branch. If the separation layer is complete, the leaves will drop to the ground.

Trees shed their leaves to prepare for harsh winter conditions by conserving valuable resources. They create this separation zone, so the falling leaves do not damage the plant in the process of shedding.

Marcescent tress do not form this abscission layer completely and so some of the leaves hang on through the winter.

As with many natural occurrences, the jury is out on the definite reason for this. Some think genetics and environmental factors are primarily responsible for the late season hangers-on, but some other hypotheses abound.

Protection:

The fact that smaller, shorter, juvenile trees hang on to their leaves makes it likely the tree is protecting buds from hungry deer through the winter. The branches of young trees are at a perfect height for browsing nutritious buds during a snowy winter. Cloaking the pointy buds in dry leaves may keep deer from eating next year’s growth.

Food:

Leaves that fall to the forest floor in autumn slowly decompose, adding much needed nutrients and organic matter to the soil. The theory is the young beech hang onto their leaves into spring so they can release the leaves to decompose after the fall leaves have already become part of the soil, thus adding a much-needed nutrient boost just in time for the spring growth spurt.

Water:

Another theory suggests leaves act as a snow fence, slowing down snow and directing it to the base of the tree as it falls, ensuring moisture through the winter and into spring.

November chores

Mums may be cut back to three inches and mulched lightly after the ground freezes.

Remove dead foliage from around rose bushes, work in some bone meal around the plant, then hill soil or mulch about eight inches deep around the canes.

Protect trunks of newly-planted shade trees by wrapping loosely with burlap or paper strips. Place wire or other protector around young fruit trees to prevent rabbit and mice damage.

All vegetable garden refuse should be cleaned up and added to the compost.

After a few frosts, cover strawberry beds with straw, pine needles or other coarse litter.

Clean up and destroy diseased and insect-infested foliage and fruit from the garden.

Lawns should have about two inches of top growth to go into the winter to prevent matting.

Leaves raked up can be added to the compost pile or used as mulch.

Use cold frames to store plants that need protection.

“Growing Green” is contributed by Diane Dorn, Lehigh County Extension Office Staff, and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613.