Creating a raised bed around a mature Western Red Cedar - Ask Extension
I would like to create a raised bed, approximately 6 to 8 inches deep with four-way soil, around an existing mature and seemingly healthy Western Red ...
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Creating a raised bed around a mature Western Red Cedar #619006
Asked March 26, 2020, 4:27 PM EDT
I would like to create a raised bed, approximately 6 to 8 inches deep with four-way soil, around an existing mature and seemingly healthy Western Red Cedar. I am concerned, of course, about the potential bark damage from moisture and whatever other problem that may lurk as an unintended consequence. Your comments will be greatly appreciated. Thank-you.
Whatcom County Washington
Expert Response
Thank you for your question. You are wise to think about unintended consequences--both for your tree and the raised bed garden plants--in planning this project. In addition to increasing the potential for insects and pathogens (fungi, bacteria and viruses, for example) of getting into the bark, you may also be risking interference with one of the most important (and unseen) characteristics of these amazing trees--the roots!
Shallow roots absorb water that drips off the trees from winter rain and summer fog. In regions without summer fog, redwoods need irrigation. Shallow roots absorb necessary oxygen from the top layers of soil. The top layers of the soil are more oxygen-rich than the deeper layers. oxygen from the top layers of soil. Extensive shallow roots form a dense mat that helps keep redwoods from falling in storms and floods. (https://arboretum.ucdavis.edu/sites/g/files/dgvnsk1546/files/inline-files/redwood_exhibits_0.pdf)
Adding additional soil near the trunk will change the depth of the roots, the amount of water getting through to them, and decrease soil oxygen essential to the tree. In addition, the 'new' plants will use up water and nutrients, and potentially interfere with the tree's root structure.
Another potential factor (but subject to some debate in the research community) is the degree to which the tree's roots may contain chemicals that impeded plant growth in other species (called alleleopathy). This is best known in walnut trees. It is believed that this characteristic emanates from the roots, so the very plant whose appearance you wanted to improve may kill your new plants. And, finally, you undoubtedly know that these trees produce an emormous amount of shade throughout all seasons. So, even if the other factors weren't enough, very few plants (and virtually no flowering ones) will bloom. This is why redwood forests have very few other species than ferns, rhododendrons and various berry plants near them.
So, you might want to consider acquiring some moss to plant around the tree. It has virtually no root system, so won't compete with the trees'. Good luck!
Shallow roots absorb water that drips off the trees from winter rain and summer fog. In regions without summer fog, redwoods need irrigation. Shallow roots absorb necessary oxygen from the top layers of soil. The top layers of the soil are more oxygen-rich than the deeper layers. oxygen from the top layers of soil. Extensive shallow roots form a dense mat that helps keep redwoods from falling in storms and floods. (https://arboretum.ucdavis.edu/sites/g/files/dgvnsk1546/files/inline-files/redwood_exhibits_0.pdf)
Adding additional soil near the trunk will change the depth of the roots, the amount of water getting through to them, and decrease soil oxygen essential to the tree. In addition, the 'new' plants will use up water and nutrients, and potentially interfere with the tree's root structure.
Another potential factor (but subject to some debate in the research community) is the degree to which the tree's roots may contain chemicals that impeded plant growth in other species (called alleleopathy). This is best known in walnut trees. It is believed that this characteristic emanates from the roots, so the very plant whose appearance you wanted to improve may kill your new plants. And, finally, you undoubtedly know that these trees produce an emormous amount of shade throughout all seasons. So, even if the other factors weren't enough, very few plants (and virtually no flowering ones) will bloom. This is why redwood forests have very few other species than ferns, rhododendrons and various berry plants near them.
So, you might want to consider acquiring some moss to plant around the tree. It has virtually no root system, so won't compete with the trees'. Good luck!
