Feeding Trees - The Root of the Matter
The trick to feeding trees lies in their roots
In a good soil, roots often grow wider than the canopy. From one-half wider than the dripline (the edge of the foliage) to as much as three times further — and in special cases, much more than anyone would imagine. If you add a barrier (as shown here) such as rock, bedrock or caliche (hardpan); the roots wander even further from the canopy looking for food.
A deep sandy soil has little resistance to growing roots and allows for root exploration of three or more times the width of the tree. Whereas, like a gardener trying to dig heavy clay soils, roots don’t like clay either and don’t make much headway — maybe growing only one-half the width of the foliage. The canopy of a walnut tree with a radius of about ten-to-15 feet had roots that extended for 51 feet away from the trunk before the researchers finely gave up digging - and the root was still one-half inch in diameter.
Some more examples include:
- Popular (Populus generosa) can have 77% of its roots beyond the dripline. Another study found that 35% of popular trees grew roots greater than two times the distance from the trunk to the edge of the foliage.
- Colorado Blue Spruce (Picea pungens ‘Glauca’) have 60% of their feeding roots beyond the dripline.
- With Green Ash (Fraxinus pennsylvanica) the roots were 1.68 times the radius of the dripline.
- The glorious Magnolia (Magnolia grandiflora) has roots 3.77 times away from the dripline.
- Sugar maples (Acer saccharum) roots have been found 30 feet from branch tips.
- Honeylocusts (Gleditsia triacanthos) reach nearly three times beyond the foliage. So, place you fertilizer and mulch at and beyond the dripline for the best effect. Also water beyond the foliage to keep the tree even happier.
BIO: Robert Kourik's books, blogs, and articles bring science to gardening. He has designed gardens for three decades and is a pioneer of edible landscaping, the art of growing food plants among ornamental plants. He works throughout California and the country. Visit Robert's blog Garden Roots or go here to buy his books.
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Comments (2)
The root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial (growing above the ground) or aerating (growing up above the ground or especially above water).The major functions of roots are absorption of water and inorganic nutrients, anchoring of the plant body to the ground and storage of food and nutrients and to prevent soil erosion.
Roots are the principal water-absorbing organs of a plant. There are three primary functions of roots: (1) to anchor the plant to a substrate, (2) to absorb water and dissolved minerals, and (3) to store food reserves. Typically we see roots in soil, but there are specialized types of aerial roots (air roots) that enable climbing plants and epiphytes to become attached to rocks, bark, and other nonsoil substrates.