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Re: problem tree roots

As others have said, there's not a really grand way to discourage
tree roots.  I garden in soil that is nothing but an interwoven mat
of tree roots.  Different trees have different levels of tolerance to
having major portions of their roots removed.  For instance, you can
hack a maple's roots regularly and it does not seem to mind; just
quickly makes more.  However, if you hack off large roots from a
tulip poplar, it resents it a great deal and major branches will die
and fall off over a period of several years.  I don't know about ash,
as I don't have any.  You might keep an eye out for branch death over
the next couple three years and if a branch looks like it's not
leafing out properly, get it removed.  You'll want to prune this tree
up anyway if branches are lower than 10 or 15 feet off the ground so
what you plant under the tree gets adequate air and light.

I know a very fine gardener who has been making raised sand/peat beds
to grow some amazing plants.  He does this on the natural grade. 
Recently, he's been putting down 6 mil black plastic before he builds
the beds, to keep out tree roots.  He says in a few years, the trees
send roots up over the plastic!

I believe this - I've had them send them up through black plastic, in
fact, so I don't advocate putting it or geo fabric down - roots will
find a way through them and then you have a real mess if you want to
ever rebuild the bed or try to transplant a shrub or something.

If you raise or lower grade significantly around a mature tree, you
have to realize you are taking a chance on its dying at some point -
earlier than it might otherwise.  I have, however, built raised beds
around large trees - but NOT all the way around them.  If you leave
3/4 of the root system where it is at the current grade, most trees
do not object to a raised bed over the rest of their root system, if
it's not too deep and the infill soil is a light mix.  In fact, some
revel in it (maples).

You will find that within in one or two seasons, your lovely raised
bed is full of tree roots.  However, that one season is often enough
for any perennials or shrubs you plant to become established and they
will do just fine if they are not plants who can't handle tree root
competition in the first place.

You will also find that the soil in your raised bed will sink - as
much as 6" - in a season or two.  You can keep on adding organic
material as mulches; helps some but does not stop the soil compacting
down.  Periodically, I find I have to go into beds under trees and
dig up the perennials and add new soil to top them up.  I seldom do
an entire bed at one time, but every time I muck with a bit, I top it

Most tree feeder roots are in the top foot of soil.  They will extend
out at least 2.5 times the diameter of the crown.  About the only
thing that will really stop them, I think, is a concrete wall going
down at least 18".  Support roots will go down further than that for
a large tree, but feeder roots, which are the ones that get into
stuff, are generally in the top layer of soil.  This is why trees die
if the grade is raised over their roots - the feeder roots suffocate.

So, IMO, just build your wall and your bed and don't worry about the
tree roots; they are just something you will have to live with:-)

Marge Talt, zone 7 Maryland
Editor:  Gardening in Shade
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> From: Theresa <tchessie@comcast.net>
> HI all-
> I am wondering if anyone knows tricks to prevent tree roots from
> in unwelcome places (but without actually killing the tree).  There
> several roots in the way of my retaining wall around the front
yard, which I
> will chop off, but am worried a million more smaller roots may
sprout from
> where I cut them off.  I was thinking the filling in around them
with gravel
> mix (so there are low nutrients available- thus making it
inhospitable for
> regrowth).  What do you all think?  Any experience with this.
> Theresa

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