Four Key Factors for Vibrant Fall Color

We all know amazing fall color when we see it: vibrant yellows, oranges, and reds against a bluebird sky or brightening up a cloudy day. But do you know the factors that contribute to these colorful displays?

Day Length

Day length, also known as photoperiod, is a crucial factor that contributes to the display of fall color.

The sky fades in color from top to bottom, going from greyish purple to orange. There are a few clouds on the horizon.

Below the sunset, the Japanese Garden with a variety of orange, red, and yellow trees and bushes. The setting sun and plants are reflected in the rippling surface of a large lake. — *The sun begins to set on the Japanese Garden. Photo by Kristina Schall DeYong/ Missouri Botanical Garden*

Shorter days trigger the formation of a special layer of cells at the base of the leaf called the abscission layer. This cuts off the supply of sugar and water to the leaf, which means that no new green chlorophyll pigment can be created.

Once the remaining chlorophyll is broken down, yellow and orange pigments called carotenoids can shine through. Red pigments called anthocyanins are also produced at this time and may protect the leaf from UV damage while it completes the process of dropping, kind of like a red sunscreen.

Temperatures

The weather is another important factor that can affect how vibrant fall foliage is any given year.

A group of fallen yellow maidenhair leaves is clustered on the ground under snow. The fall color has begun to fade. — *An early frost can put an early end to fall f*oliage. Photo by Kelly Cato/ Missouri Botanical Garden.

The ideal weather for good fall foliage is warm, sunny days with cool nights. If the weather is too hot or too cloudy, the color may be more muted. An early hard freeze could put a premature end to the vibrant show.

Precipitation

Precipitation is also important for fall color. Drought can cause leaves to scorch or drop early without showing off their true colors.

A rainstorm covers a large lake surrounded by vibrant red and orange trees. The surface of the water shows where rain is hitting the usually still surface. — *Consistent rainfall in the late summer and early fall can help fall colors shine brighter. Photo by Kent Burgess/Missouri Botanical Garden.*

Even weather conditions in the spring can have an impact on fall foliage later in the year. A wet spring could encourage the proliferation of fungal diseases such as powdery mildew and anthracnose. Leaves damaged by these infections tend to have less vibrant fall colors.

Plant Species With Great Fall Color

Even with the perfect conditions, some plants won’t shine every fall.

Some plants will reliably produce excellent fall color almost every year. Others may have some years with a good color display, and some where the colors leave something to be desired.

Still other plants do not produce much fall color at all. Here are a few trees and shrubs that are great choices for the St. Louis area and will put on a show just about every fall.