Ask Mr. Smarty Plants

Let's address the acacias first, as you may be making the decision to remove some of them. There are two acacias native to California; most of them are native to Texas only, or Texas and New Mexico. The reason for this is that we are already used to having vicious thorns, sometimes hooked spines, that tear at clothes and person. Acacia farnesiana (sweet acacia) can grow to 15', and Acacia greggii (catclaw acacia) is usually a mounded shrub to about 5' tall, with the worst thorns, which are blamed for making it the most despised shrub in the Southwest.  So, while we are glad some of the ones you have are doing well, we certainly wouldn't recommend planting any more, unless you're landscaping Sleeping Beauty's castle.

On to the soil which does not drain well. We are going to suggest shrubs or small trees that will tolerate a clay soil, which is usually the culprit in poor drainage. However, since you really shouldn't attempt to plant your hedge until after the last freeze date for your area in Winter, that will give you time to amend that soil a bit. Digging a long trench where the "fence" is going to go and mixing in compost, leaf mold or some other organic material with the native soil will not only go a long way toward improving the drainage, but should make digging the holes for the plants easier when the time comes. Add more organic material as you plant, and mulch with a shredded hardwood mulch, to shelter the roots from cold and heat, and help hold moisture in. The mulch will continue to decompose and add to the improved texture of the soil. 

We are going to go to our section on Recommended Species, click the map on Southern California and Narrow Our Search on Habit of Shrub and Tree, although we only found one tree of acceptable height, and look for appropriate plants that are adaptable to clay soils. We are a little puzzled about your temperatures going below freezing every Winter, since you are almost on the Pacific Coast and pretty far south, unless you actually are located in some of the mountains above Ojai Valley. We'll take your word for it. We chose only evergreen plants, since you are looking for privacy, summer and winter, and also looked for plants that could take lots of sun but tolerate some shade and not very good, dry soil. Read the webpage that is linked to the plant name, and for more information, you can go down to the bottom of that webpage, and click on a link that will take you to a Google search on that plant. You will then be prepared to make your own decision based on habit, projected height, etc. 

SHRUBS

Arctostaphylos manzanita (whiteleaf manzanita) - 6 to 12', generally branch or fork near ground, pictures

Carpenteria californica (tree anemone) - 4 to 8' 

Ceanothus impressus (Santa Barbara ceanothus) - 6 to 8'

Heteromeles arbutifolia (toyon) - can grow 15 to 20', bright red berries

Juniperus californica (California juniper) - 10 to 15, pictures

Morella californica (California wax myrtle) - densely bushy, 10-25', aromatic leaves, attracts birds, pictures

TREE

Cercocarpus montanus var. glaber (birchleaf mountain mahogany)

When you have made some selections, you can go to our Native Plant Suppliers section, type your town and state in the Enter Search Location box, and you will get a list of native plant nurseries, seed companies and landscape consultants in your general area. 

Carpenteria californica

Ceanothus impressus

Heteromeles arbutifolia

Cercocarpus montanus var. glaber