Sadly, few people still realize how a tree's roots actually grow. The color illustration was to advertise a local garden tour in 2009. Notice the roots don't extend beyond the dripline of the foliage. No way. As seen in the illustrations below roots extend far beyond the foliage. (The other 2 B&W illustrations come from my book - Roots Demystified. The one on the left shows the dripline as a dotted line and the roots beyond..)
When I had a landscape maintenance company, I soon discovered that in a good soil, a tree’s roots will often grow to occupy an underground area wider than its dripline. If led by available moisture and nutrition, a tree may tunnel its roots through soil space ranging from an area one-half wider than the dripline to as much as three times further. In special cases, tree roots may ramify much more than anyone would imagine. If you add a subsoil barrier such as rock, bedrock, or caliche (hardpan), a tree’s roots will wander even further beyond the canopy area in search of food. A deep sandy soil offers little resistance to growing roots and allows for root exploration of three or more times the width of the tree. And, like a gardener struggling to dig heavy clay soil, roots don’t like clay either and don’t make much headway through it, perhaps only one-half the width of the dripline.
Some more examples include:
- Poplar (Populus generosa) can ramify 77% of its roots beyond the dripline.
- Another study found that 35% of poplar trees grew roots greater than two times the distance from the trunk to the edge of the foliage.
- Colorado blue spruce (Picea pungens ‘Glauca’) grow 60% of their feeding roots beyond the dripline.
- White green ash (Fraxinus pennsylvanica) grew roots which were 1.68 times the radius of the dripline.
- In one study, the glorious magnolia (Magnolia grandiflora), had grown roots 3.77 times wider than the dripline.
- Sugar maples (Acer saccharum) produced roots that have been found spreading underground 30 feet beyond branch tips.
- The roots of honey locusts (Gleditsia triacanthos) can reach nearly three times beyond the dripline of the foliage.
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Visit my web site to learn about my new book on drip irrigation and other gardening books.
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
