Tuesday, May 27, 2008

Taproot Myths Revealed


This is a photograph of a young tan-oak seedling, sometimes called tanbark trees as their bark was stripped off and used to tan animal hides. These trees used to be classified as a species of Quercus (oak), now reclassified by botanists with time on their hands as Lithocarpus densiflorus. Don’t ask me why. This seedling has a stem with a few leaves five inches above ground and seven inches of a taproot, all I could dig out. (Click on the photo to see a much larger image.)

In my book, Roots Demystified, change your gardening habits to help roots thrive, I talk about how few trees actually grow with taproots. Oaks are an exception, for awhile.

Some Californian and western oak trees (including the tanbark oak), begin growing with a taproot, which then naturally atrophies. The loss of the taproot can begin as early as the first or second season. When the young seedling of a blue oak is a mere three inches high the taproot can already extend 40 inches into the soil. After a number of years, the taproot withers, to be replaced by heart roots (which angle down from the base of the tree) and many laterals, with vertical sinker roots. In Spruce (Picea spp.), Hemlock (Tsuga spp.) and Cedar (Cedrus spp.) trees, at less than eight years, the lateral and oblique roots take over the role of support and the taproot declines. (From: “Natural Root Forms of Western Conifers”, S. Eis; From: Proceedings of the Root Form of Planted Trees Symposium, page 24, 1978.) After the taproot atrophies, the new root system grows more horizontal and oblique roots and resembles a fibrous root system.

In my photograph the roots are about as long as the stem and leaves. However, much of the tiny taproot was left in the ground judging by the thickness of the bottom of this seedling as it was dug with a spading fork. The seedling sprouted in deep shade which probably accounts for the extended length of the stem.

Any oak planted from any container or balled-and-burlapped stock has effectively had its taproot destroyed and forms a fibrous (heart roots) root system.

I think the sturdiest oaks are grown like nature, from seed placed where you want a specimen for your grandchildren to climb on.


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NOTE: The comments section at the bottom of the post has disappeared. Click on the "___ Comments" button or the title under the "Blog Archives". Thanks, Robert

2 comments:

Martha said...

Thank you, I'm attempting to write a chidren's book on the mighty oak, and had Quercus douglasii in mind as that's what we have in our front yard. Even though I have a BS in Ornamental Horticulture, I was not aware that the tap root withered. Thanks for some good info!

Jeanine said...

thank you... buying trees for my yard and learning more about roots.. good information.