Re: Walnut Confusion

Elle,

Lisa made a very good point.  The roots from the walnut tree will eventually 
grow up into your new raised bed.

Also, keep in mind that a tree's roots are not confined within the dripline.  
Usually the roots grow in an area two to two-and-a-half times the diameter of 
the dripline.  An average mature black walnut will have toxic effects for a 
radius of 50 to 80 feet.

However, since there are roses, hawthorns and holly growing under it,  it 
seems to me likely that yours is not a black walnut.   If these plants are 
healthy and have been there for a few years, I think you can be sure of it.  

But there is another problem to think about before you finalize your plans.  
You mentioned you were planning to backfill 4' from the tree.  Please be 
careful!  Contrary to popular belief, the majority of a tree's roots are 
within the top 12 inches or so of soil.  There they can get oxygen as well as 
nutrients and water.  Changing the grade level within the root zone of a tree 
is very dangerous.  Raising it can easily injure or kill the tree by 
suffocation.  If you do decide to do it, you should not add more than a few 
inches of soil.  I wouldn't raise the grade more than 4" if it were my tree.  
You can gradually raise it more, giving the tree a season to grow new roots 
with each increase.  But sudden, drastic changes are not recommended.  

I know many people routinely put high stacks of mulch under their trees with, 
seemingly, no ill effects.  But it often takes a mature tree many years to 
die.  It will put much energy into surviving in adverse conditions, but it 
will be stressed and will gradually decline, become vulnerable to diseases 
and pests, and ultimately die.  

Now that I am discussing tree care, I am getting off topic, but so many of us 
garden under trees that I though this was of interest.  --Janis


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