Here’s a recent question that opens up a good subject:

Bill, When a tree (Shamel Ash) is cut down and the trunk is ground out, do the roots keep growing? — P.V.

The roots do not keep growing if the stump is ground out and if there are no sprouts above ground.

Why?  There are two reasons:

 1.  Leaves and green stems utilize sunlight in photosynthesis to feed all parts of the tree, including the roots. Without foliage  (or green stems) roots starve.

 2. Sprouts and leaves come from buds, which serve as backup survival mechanisms. If there are no buds on a branch, trunk, stump or the roots, there can be no sprouts.

 No buds: no sprouts. No sprouts: no leaves. No leaves: no food for the roots.

Some trees, like most pines, true cedars, cypress, junipers, and many other conifers lack buds at the base of the trunk, in the roots and even in the bare portion of the branches above ground. It is just a natural aspect of their anatomy.

Have you ever noticed how some trees and shrubs — especially the evergreen conifers mentioned above  —  lose inner foliage and branches as they age, and they just won’t sprout and fill in inside, no matter how hard you prune them back? It’s because there are no buds on the bare branches. The same goes for their roots. When you cut them down, there are no buds to sprout and form new shoots.

In contrast, many tree species — mostly the  broadleaf deciduous trees, broadleaf evergreens, and some evergreen conifers like coast redwood —  readily sprout when they are pruned back or broken off at bare wood or cut down to the ground. Many of our local coast live oaks, California bay laurels and coast redwoods are “second growth” trees; stump sprouts that became trees.

Those sprouts arise from “dormant” buds, which serve as backups that may lie waiting for many years to be released and grow when portions of the tree above them are lost.

A different kind of buds, “adventitious” buds, form irregularly on various parts of a tree. Root sprouts, also known as “suckers” arise from adventitious buds. These are common on crabapples, quaking aspens, Lombardy poplars, Liquidambars,Tree of Heaven and others. Again, they serve as backup survival mechanisms. Of those, the Tree of Heaven and Lombardy poplar are notorious locally for producing suckers far from the stump.

If the question is “How do I get rid of this tree and keep it from sprouting back?” you need to know a bit about the tree species and then plan accordingly.

When a  non-suckering tree, like the ash, is taken down and the stump is ground out, the roots eventually starve and become food for other organisms in the soil. That brings us to another question. What are the potential plant health effects of stumps left in place?

 At this time of year, with the onset of the rainy season,  we often see sudden flushes of mushrooms in a lawns where trees were removed. My own front lawn is an example. Roots of the birch trees we removed years ago are still feeding the the fungi that  generate mushrooms every fall. Mushrooms in lawns, often mistaken to be a lawn disease, are usually just  a sign of decomposing dead tree roots.

In some cases, a dead stump can become a disease center. For example, California native oaks are resistant to oak root fungus (Armillaria) until they begin to decline for any of various reasons,  environmental conditions favor the fungus, or the tree is cut down and the stump left in place.  Small lesions of Armillaria, which are generally present and inactive on healthy oaks, expand, slowly devour the stump and roots and attack susceptible tree and woody plant species nearby, especially if there is summertime moisture from irrigation in the area. It is a common challenge for homeowners and growers of grapevines and olive trees.

In cases like that, it is best to have the stump and roots excavated and removed, or to grind them out as much as possible. Otherwise, the fungus persists, for decades or more, in dead roots.

Analogous to dormant buds, oak root fungus patiently waits and then begins to grow when conditions are favorable.

Bill Pramuk is a registered consulting arborist. Visit his Web site, www.billpramuk.com,    e-mail questions to info@billpramuk.com , or call him at 226-2884.