Seeing red – in autumn leaves and in misdiagnoses

Existential dread – the botanical version. (Thanks to Tommy Siegel’s creative talents)

While the onset of autumnal leaf color change reminds us that winter is coming, there are many other reasons why leaves turn red. Knowing why and how leaves turn red is key in accurate diagnosis.

Once near-freezing temperatures occur, leaves seem to turn red overnight.

These are examples of leaf reddening misdiagnosed as phosphorus deficiency:

The leaf reddening in all of these photos of “phosphorous deficient plants” is actually due to water stress.

These leaves are not phosphorus deficient, either.

Leaf reddening here is due to solar damage (leaf scorch)

Congratulations to accurate diagnosticians at UCANR! This is indeed phophate deficiency. Damage is not localized as in the previous images.

Lack of sufficient phosphate causes overall leaf reddening among other symptoms.

Here are some other underlying causes behind leaf reddening.

This Cornus kousa (dogwood) is sitting in a perched water table. Poor soil drainage is causing anthocyanins to accumulate at the margins of the leaves.
Leaf reddening on a Cornus spp. (dogwood) suffering from anthracnose

If you’re interested in learning more about how and why leaves turn read, be sure to download my most recent factsheet, appropriately titled “Why do leaves turn red?” ] It’s peer-reviewed and relevant to any part of the world.

Enjoy this Halloween treat!

Published by

Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

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