The "How and Why" of Fall Color

Posted by Annie Napier on 11/06/2017

Trees seem to be ablaze with color and we don't always get this show here in Oklahoma, so I wanted to explore just precisely why this deciduous foliar show is happening.


 

The answer is: Many environmental factors determine the color, the intensity and the duration of brilliant and transient autumn leaf colors.  

1) Most importantly are adequate amounts of soil moisture. 

2) Temperature.  Warm days with bright sunlight, and cool nights, to be exact.

3) Seasonal change in light level.

A protective function of the cells in a leaf abscission layer begin to seal off the flow of water into the leaf in the fall, this also prevents the outflow of sugars that were manufactured within the leaf. Chlorophyll pigment is reduced in the leaf as it dehydrates and we begin to notice all of the pigments that have been hiding because chlorophyll's pigment buddies, over 80 different types of carotenoids and xanthophylls, break down more slowly than chlorophyll.

  • Beta-carotene (1 type of carotenoid) contributes orangish-yellow and orange
  • Lutein (1 type of xanthophyll) is uncovered to produce bright yellow 
  • Tannins reveal golden and brown color, as well as make foliage unpalatable to herbivores and insect pests, and give leaves an antimicrobial superpower to protect against disease-causing organisms.
  • Anthocyanins pigments are produced from the glucose that remains trapped in the leaves.  Here is where the brilliant red and purplish-red fall color come from.  Trees that have a lot of anthocyanins have a purplish color to new growth and to mature foliage during the growing season.  During active growth anthocyanins function as sunscreen anti-oxidants.

 

Some trees we have noticed looking particularly eye catching this fall are: 

Red: Shumard oak, Red maples, 'Caddo' Sugar, and Amur maples, Crape myrtles, Chinese pistache

Yellow: Lacebark elm, Ginkgo, Sweetgum

Also noticing: Bald cypress, Japanese maple 'Sango Kaku' (coral bark), smoke tree

Shrubs: Red twig dogwoods, Oakleaf hydrangea, Virginia sweetspire, . . . Kristy is very eager to see her "Winterberry" Euonymus change color; we'll keep you posted.

Ornamental grasses:  heads such as 'Ivory Feathers' Pampas grass, to name just one.

We'd love for you to see more fall and winter interest in your project next year, contact us for a consultation to see what would work well for you! 

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