Why Do Leaves Turn Yellow on Cottonwood Trees?

The yellowing of cottonwood leaves in the fall is a natural process called abscission, which is triggered by a combination of factors, including:

- Day length: As day length decreases in the fall, trees produce less chlorophyll, the pigment that gives leaves their green color. This causes the leaves to turn yellow or brown.

- Temperature: Cooler temperatures in the fall also contribute to leaf yellowing. When temperatures drop below freezing, the water in leaves can freeze and damage cell walls, causing the leaves to turn brown and fall off the tree.

- Drought: Drought conditions can also cause cottonwood leaves to turn yellow and fall off prematurely. When trees don't get enough water, they can't produce enough chlorophyll, which leads to yellowing of the leaves.

- Nutrient deficiency: A deficiency of certain nutrients, such as nitrogen, can also cause cottonwood leaves to turn yellow. Nitrogen is essential for chlorophyll production, so a lack of nitrogen can lead to yellowing of the leaves.

In addition to these factors, some cottonwood trees may also be more prone to yellowing leaves due to genetic variations.

Leaf yellowing and abscission are a natural process that helps trees to conserve energy during the winter months when they are not actively growing. By shedding their leaves, trees reduce the amount of water they need to transpire, which helps them to survive in cold and dry conditions.