Jay wrote:

I have a big oak tree in my backyard. The lawn(bermuda) around the tree is
struggling though I have been making extra effeort on that area in the last
years. So I am having this idea of get rid of the grass abound the tree root
and create a raised bed there to plant some shade-like plants. After some
internet search, I found that it is not recommended because it may do harm
to the tree. It is suggested just put mulch lightly around the tree root.
But that looks a little dull and I really want to make it nice-looking. Any
good suggestions? Thanks.

Jay

If this is a native oak (growing naturally, not planted) and you
are in the western U.S., you can kill the tree by gardening under
it.

First of all, the tree should not be watered at all in the summer.
In the winter, you can give it one or two soakings BUT ONLY IF
there is a draught. Otherwise, native western oaks should be
allowed to go dry except for winter rains.

The best mulch for a western oak is the leaves it drops. Other
leaves can be added. Don't pack them down. To keep them in place,
you can sprinkle them very lightly with water. Eventually, the
leafs will decompose into leafmold. Western oaks thrive on this.
It keeps the soil cool in the summer and helps retain winter
moisture through the year.

If you must really plant under the tree, start with very small
plants that don't need much digging when you plant them. These
should be natives that will survive with a lack of summer water.
Watering around a naturally growing western oak will cause the tree
to rot and die. Also, the plants should be able to thrive without
added nutrients. Fertilizers (especially high-nitrogen) will also
kill western oaks.

However, if the tree was planted from a nursery container, it
should be able to withstand summer water and some fertilizer. It
should still be mulched with its own leaves. The soil within its
drip zone (the area under its branches) should be disturbed only
infrequently and not more than the top 6 inches. Plants around
such a tree should be suitable for the tree's environment: tall
enough to grow through the mulch, need only a little water in
summer, need only light feeding.

You can indeed have a lawn up to the trunk of a planted western
oak, but you need a grass that will do well in shade and part-shade
(not Bermuda). A lawn will substitute for mulch.

The major difference between a native oak and a planted oak is that
the former has a taproot while the latter generally has had the
taproot cut while being moved from a seedling container into a
larger container. Western oaks growing naturally require that
their natural environment prevail: lean soil and dry summers. This
is not true for planted oaks whose taproots were removed while
still young.

--
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 URL:http://www.rossde.com/garden/