An analysis of your situation/ the no-till system

As much as I admire, and in some situations use, the so called no-till
or lasagna system of growing, I don't think it will in and of itself solve 
your problem.

If I correctly understand your situation, you have a retaining wall
which creates a raised bed area which is in full sun and occupied
in significant part by an oak ( You did not say what kind or how large.)

Your complaint is that it is laborious to keep watered and impossible
to keep in good tilth.

I don't know what you are trying to grow in this spot, but it sounds like 
part of the problem might be what you are choosing as plant
material  or your expectations of what this area should be/ how this
area should look.

Generally, areas and beds occupied by large trees are some of the most
difficult to garden successfully.  While you don't apparently have the
problem of shade in your situation, you still have the competition
from the roots of what I assume is a native oak of enough stature that
you want to keep it and therein lies the problem.

If you have been reading this message board long enough, you have no doubt 
heard warnings about watering oaks here in California in the
summertime.  Eventually such trees succumb to one or more root pathogens
that are encouraged by soil moisture in warm temperature soils.

Now layering well composted organic material topped with a bark or wood chip 
mulch will keep the soil cooler and retain some of the winter
moisture from rainfall, as well as providing a more open soil surface
and protection from compaction (therefore better aeration and overall
plant health), but if you continue to water this you will eventually
lose the tree unless it is one of the import oaks that are adapted
to summer water. Even in this case, such a tree transpires at a phenomenal 
rate in summer, and you will be hard pressed to replace the
moisture by hand watering.

In addition you need to think about choosing plants that will grow in
competition with roots and need little (preferably no) summer water.
This seems an ideal situation for a great many geophytic plants (bulbs).
You have sunlight, obviously excellent drainage, and the raising of the
wall puts the flowers up at eye level.

A great many of the Narcissus (the tazetta in particular) would do well in 
such a spot, but there are a host of other bulbs which also will do well for 
you in Marin and will extend the flowering season, just don't pick anything 
with much of a chilling requirement like tulips.  A great many of the Iris 
will also do quite well for you in this place.

You will probably also want to fill in spots along the top of the wall
with evergreen mainstays like prostrate rosemary cascading down or
one of the drought tolerant vines, to hide the dying bulb foliage
and give some visual relief for the rest of the season.  I have also
seen lantana used to good effect in a similar situation.

Having selected such plant material, the no-till methods so ably described 
by many others will help you to grow them with a minimum of
fuss after the first year or so of establishment(always a touchy time).

At any rate, this is the approach I would take in such a case. For further 
inspiration consult any of Sidney Mitchell's books (From a
Sunset Garden, Gardening in California, Your California Garden and Mine)
which, though out of print, are well represented in the libraries and
used booksellers inventories. He gardened and wrote not all that far from 
you, in Berkeley and Oakland, in the days before automatic watering systems 
were in vogue.


Yours most respectfully,
Michael Larmer

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