It's time to dead wood those oak trees

Quercus agrifolia, California's glorious live oak, should only be trimmed in the late summer.  There is currently a fashion for lacing these trees.  Don't do it.  It is bad for the tree and can cause disease.  The only reason to prune an oak tree heavily (or any tree for that matter) is if it presents a danger for instance by overhanging a roof.   It is OK to cut limbs of less than 1" in diameter and dead wood of course, provided it's done in the dormant period in late summer/early autumn.

Use a licensed arborist to trim your valuable trees.

Trees

I don't know why it is but the sun seems more dazzling these days and my plants scorch in summertime unless they are at least lightly shaded.  Quercus agrifolia, California live oak, is the most practical shade tree in California.   Although this species has a reputation for slow growth, after the first ten years they take off like rockets and become enormous eventually.   If you plant one, choose a tree with all of its lower twigs and branches intact.  This will encourage the trunk to grow strong.  The lower branches can be trimmed off later on. The grand Valley oak grows even larger, and is deciduous (a winter advantage) but it is susceptible to oak root rot fungus and it is probably unwise to grow this beauty in a city garden.

Platanas racemosa, California sycamore is a beautiful deciduous tree with large hand shaped leaves.  It naturally grows near streams and is not drought tolerant.  Grow it if you have a spring or creek.  If this tree is stressed by drought it will suffer from blight and drop leaves at any time.  The Arizona cultivar is not as susceptible to the blight and you can recognize it because it does not have the characteristic mottled trunk of the California native.

Dry shade schemes

aloe_marlothii

winter_shady_garden

These pictures show two plantings under oak trees, the one on the left receives morning sun all year round, whereas the one on the right only gets morning sun in winter when the neighboring sycamore loses its leaves.

The characterful plants on the left never need maintenance and, after a couple of years, will virtually never need water. These are fire safe plants.

Bromeliads and many succulents (shown on the right) do well planted under California live oaks, and because they are drought tolerant and very shallow rooted they do not affect the soil negatively.

Oak Trees: plants for dry shade

It is always difficult to find plants to grow under oak trees where irrigation cannot be used.  The best plan is to stick to native plants.   However,  following is a short list of appropriate drought tolerant plants that will look good together.   Achmaeas and Bromeliads will need a sprinkle into their cups in the summer and fall from time to time, but it does not require damp soil.  

Achmaeas and Bromeliads

Aloes, various

Cycads

Dudleya lanceolata (California native)

Gasteria Mahonia repens (California native)

Rosa banksiae

Salvia Spathacea (California native)

Symphoricarpos, any (California native)

rosa_banksiae_inoaktree

Here is a California live oak with a climbing rose, Rosa banksiae lutea, weaving through its branches.  It’s wonderful to behold in springtime, and in summer the rose lies dormant and does not impact the oak at all.  The rose is quite old and grows with no irrigation at all, its roots shaded by the sheltering oak.

Careful plant choices prove that you can mix native and non-native plants with great success.  Patience is important as drought tolerant plants such as this rose must grow slowly because the root system must plunge deep into the ground in order to survive the long dry summers.

This particular rose requires no pruning as all of the growth is up in the tree.  As the rose grows slowly, without irrigation, economy of branches  is built in.

Below, on the left you will see Salvia spathacea which has a nice lush look for a dry shade garden.  Although slow in its first year, this salvia spreads laterally from roots and will make a pretty ground cover in time.

Salvia spathacea

Symphoricarpos mollis  can be found in California as well as all over the western states and its form and color varies slightly in all the different microclimates it enjoys.  In Malibu it is very green and lush under oaks in winter.

Symphoricarpus