Winter Tree Biology

Fall is the favorite season for many people because of sweater-wearing weather, cozying up to fires, pumpkins, and fall colors. Coloradans head to the mountains to see Aspens paint the side of mountains yellow, orange, and red. Biologically, hardwood trees are busy too. They drop their leaves to conserve water and to prepare for the next growing season. Bare trees are excellent candidates for winter tree pruning.

hardwood tree leave abscission

Why Do Hardwoods Drop Their Leaves?

If you ask a certified arborist or a biologist why trees drop their leaves, they will say it is all about biochemistry and biological advantage. Cooler weather triggers hormones to start a process called Abscission. Abscission comes from Latin, which means to cut off or scissor. The process begins with the absorption of Chlorophyll from their leaves back into their root systems. Cells start to grow where the leaf stem attaches to twigs or branches. These cells cut off all nutrients to the leaves, causing them to dry up and become brittle. It is just a matter of time before a gust of wind knocks them off. These cells form a protective layer protecting the tree from water loss.

What is the Biology of Fall Leave Color?

Tree leaves are full of chloroplasts that use photosynthesis to feed the tree and release oxygen into the atmosphere. Chlorophyll, a green pigment, absorbs light to fuel the process of converting water and carbon dioxide into sugars that feed trees. As mentioned above, Abscission absorbs Chlorophyll back into the tree. Without the green pigment, the leaves are no longer green. Two categories of compounds produce the bright colors of fall: Carotenoids and Flavonoids. Carotenoids assist Chlorophyll in absorbing light and protecting leave tissues from electromagnetic radiation emitted by the sun. Our eyes see orange because of the pigment’s ability to reflect red and yellow light. Various classes of Carotenoids turn Aspens yellow and orange in the fall.

Anthocyanins, a Flavonoid, helps Chlorophyll absorb light and turn leaves brilliant red in the fall. Trees use Glucose, a vital nutrient, to produce Anthocyanins to turn leaves red. Red leaves attract animals to eat tree fruits and distribute seeds. Also, these compounds protect tissues from high-energy ultraviolet light after the absorption of Chlorophyll.

Why Do Evergreens Stay Green?

Pine, Fir, and Spruce trees are common in colder climates in North America. Conifers use biochemistry and leave structure to reduce water loss during the cold months of the year. Their long, thin needles have less surface area to lose water compared to broader hardwood leaves. Conifers also coat their needles with Cutin, a waxy polyester, to help prevent water loss. Evergreens use Glucose and proteins to lower the freezing point of water in the tree. These compounds protect wood cells from bursting when temperatures drop below freezing. Also, these antifreeze compounds keep water available for photosynthesis during the winter months. So, homeowners need to water their Pine, Fir, and Spruce trees in the winter.

ash tree bud

How Do Deciduous Trees Prepare for Growth in the Winter?

Most hardwood trees bud in late summer to prepare for the next growing season. They protect their buds with scales to seal them against cold weather. Inside the buds are tightly packed leaves and flower tissues that burst open once the weather warms again. Since buds are apparent, the late fall or winter months are an excellent time to prune trees.

What are the Benefits of Winter Tree Pruning?

Trees lay dormant during the fall and winter, so tree trimming at this time does not stimulate additional growth. It is important not to prune trees too early in the fall because hard freezes will kill off any new shoots. Winter pruning gives trees time to heal before spring comes. Below are six benefits of winter pruning:

  1. Easier To Evaluate Tree Structure

    It is easier to see a tree’s structure and identify any problems once its leaves drop. We cut out any plants’ dying parts and eliminate any rubbing branches, limbs growing towards the center, branches with narrow crotch angles, and limbs that pose hazards to people or property. Newly planted trees benefit from winter trimming because it sets them up for a successful growing season.

  2. Trees Look Better

    After a winter rejuvenation pruning, the remaining branches’ buds produce healthier leaves, fruit, and limbs. Winter pruning also avoids the “stick look” of a tree heavily pruned in the spring or summer.

  3. Saves Money

    Winter is ideal for big tree jobs because the ground is frozen. Since the frozen ground allows us to stage equipment next to a tree, the job goes faster, lowering job costs.

  4. Less Tree Stress

    Research shows that pruning during the winter months leads to faster wound closure. When springtime comes, the healed wounds keep out destructive insects and pathogens.

  5. Avoids Spreading Diseases

    Many common tree diseases are inactive in the winter. So winter, it a perfect time to prune out dead wood, cankers, and other parts of the affected trees.

  6. Prevents Winter Damage

    Denver’s heavy snowstorms cause mechanical tree damage. Winter pruning takes out any branches most likely to break, making the tree less susceptible to snow breakage.


What Are The Benefits of Hiring a Licensed Tree Company For Winter Pruning?

Homeowners need to take quality, safety, licensing, and reputation into consideration when hiring a tree company for winter pruning. They should hire an experienced tree service company for the following reasons:

  1. Trees Are Valuable Assets

    According to home appraisers, a mature tree landscape is worth the cost of a new car. Since trees are valuable assets, it is smart to hire a tree service company that knows what they are doing.

  2. Tree Work is Hazardous

    Tree work is hazardous because of the risk of falling and the use of sharp, powerful machinery. It is best to hire a professional company that takes job safety seriously.

  3. Complex Tree Health Issues

    Sometimes, it takes a certified arborist or a plant health care professional to spot a tree insect or disease. The breeding cycles of tree pests makes treatment timing complicated, and some tree ailments are persistent and difficult to cure. Also, dealing with large trees requires bucket trucks to reach high into the crowns of trees. Do It Yourselfers do not have the equipment to get into large trees.

  4. Large Tree Pruning 

    Ross Tree is known for its ability to do jobs in tight places or next to busy streets. Homeowners with large trees needing pruning should check out our Large Tree Job Handbook for more information.

Ross Tree has three ISA certified arborists and has an excellent reputation in Denver. Homeowners wanting to get their trees trimmed in the winter, please fill out this tree service request form or call 303-871-9121.