On 9/17/2008 8:54 AM, Henry VIII wrote:
We have just moved to a new home that has two fifty-foot eucalyptus trees in
the back yard about 20 feet from the house. The area where the trees are is
plain dirt that has never been planted/irrigated. The tree roots do not
appear above ground.

We'd like to pour concrete in the back yard area to make a patio. Any
suggestions on what to do or not do when laying out the concrete forms such
as minimum distance to the trunks?

The trees have been here a long time and we don't want to do anything that
will injure them. This is in Los Angeles.

Thanks.




Paving in the root zone of a tree -- even when the roots are deep -- is
NEVER a good idea. There are alternative ways to make a patio in that
area that do not involve poured concrete.

I suggest you frame the area with a composition board (not wood) or a
concrete curb. Then level it by pouring pea gravel within the frame.
You don't want to add so much gravel that it comes to the top of the
frame, just enough to make a level base.

Then, you have some choices.

You can lay unmortared brick on top of the gravel. Use a broom to brush
dry sand between the bricks to lock them in place.

You can lay concrete blocks. Use the thinner blocks that are only 4
inches high with the holes up (not the standard 8 inches). Fill the
holes 3/4 to the top with more pea gravel and then finish with
decomposed granite (DG). Rinse the DG into the gravel and add some
more. Repeate until you have a level surface.

Top the gravel with DG. Rinse, tamp, rinse, tamp, etc. Add more DG to
bring the whole thing to the height you want. Eventually, you will get
a surface that is firm enough to hold a table and chairs (choose
furniture with broad feet); you will even be able to rake it. You might
want framing within the patio, which will provide both decoration and
stability.

Lay field stone or irregular broken pieces of concrete with DG between.
Again, you will have to rinse, tamp, etc.

All of these will permit rain to penetrate the patio to irrigate the
tree roots below. They will also allow oxygen into the soil.

--
David E. Ross
Climate: California Mediterranean
Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean
influence (USDA 10a, very close to Sunset Zone 19)
Gardening pages at http://www.rossde.com/garden/