Inpreparing for a consultation for another site under native oak trees at risk for SOD I found the latest host list published by the Sudden Oak DeathTask Force . The new list updated March 2008 also lists plants naturally infected and lots of information re. spreading the fungus as well as tips on sanitation. The latest information on prevention and keeping the immune system of your trees up if also available. I did find that a few of the plants that I was going to recommend for homeowners with oaks on their property have now been listed as vectors. They are coffeeberry, toyon, berberis aquifolium, manzanita and some varieties of ceanothus. This is important information for all of us to know.
We are all interested in unthirsty plants these days. When I design gardens under our native oaks there are several principles that I follow that I want to share with you. Drought tolerant plants are a must in this situation. Evergreen oaks even have special needs requiring a different plant palette than deciduous oaks like blue and valley oaks.
Most oak roots are in the upper 3 ft of the soil. The roots which take up water and nutrients are in the upper 12". The critical root disease zone for an oak is within 6-10 ft of the trunk. Do not irrigate plants or disturb the soil in this area. Outside this zone but within the drip line one deep watering per month is allowable for your plantings.
The leaf mulch that accumulates under a large coast live oak increases soil moisture and available nutrients, improves soil structure and moderates soil temperature. It’s a valuable resource that can be used in other parts of the garden. Never remove the entire insulating layer of leaves from under a trees canopy and don’t allow leaf mulch to cover the trunk.
One of the showiest California natives for planting under a coast live oak is carpenteria californica or Bush anemone. This evergreen shrub is resistant to oak root fungus and grows in sun or shade. Although this plant can get by with no summer water after becoming established, occasional summer water will help maintain a fresher look. The compact variety ‘Elizabeth’ produces a profuse display of white flowers with as many as 20 flowers per cluster. Cut back the top 1/3 to 1/2 of the stems after flowering to keep it compact.
Another deer resistant plant I like to use under oaks is Centennial ceanothus. This gopher resistant low spreading groundcover grows 12" high and 8 ft wide. Cobalt blue flower clusters cover the plant each spring. They also attract birds.
Western redbud can be grown as an accent shrub or small tree under coast live oaks. Large bluish grey rounded leaves have heart-shaped base making quite a show among smaller leafed plants. The magenta sweet-pea shaped flowers cover the branches in spring. Scattered flowers may also appear in late summer and fall. Flattened seedpods rustle in the wind in late summer and fall. And if that’s not enough to love about western redbuds they brighten the landscape with a fall color display of yellow or red leaves. Western redbuds respond well to pruning. Thin the oldest trunks each year to keep them growing vigorously. You can also cut the entire clump to the ground to rejuvenate it. This is truly a four season plant.
Combine any of these plants with coffeeberry, native irises, pink-flowering currant, toyon, berberis aquifolium, snowberry, hummingbird sage or yerba buena to complete your woodland garden and keep your oaks happy too.
Visited a site yesterday under dozens of huge native oaks. The clients wants to plant a little landscaping here and there to enhance her property but not endanger her oaks. Naturally both deer and gophers abound. The deer trail goes right below her deck. I was able to give her some information about planting near oaks and will develop a plan for her installer to follow. There are several plants like mahonia ( now berberis ) that would require little water after becoming established and also I am considering ceanothus ‘Centennial’ for an area below the flagstone landing. I’ll add more to this post as I develop the planting plan for this beautiful property.
In writing one of my weekly columns for www.pressbanner.com/, I researched problems that occur with hedges and thought it would be interesting to share this info here:
To care for your hedge. Hedge plants should be pruned back by about a third when they are first set out. The second year, trim the hedge lightly to keep it dense as it grows. Don’t try to achieve the hedge height you want too quickly. Keep shearing lightly to keep the hedge thick without gaps as it grows to the desired height.
Once the hedge is as tall as you want it, your pruning technique should change.
Small leafed hedges should be sheared lightly whenever they look ragged. You can, if you want, simply allow the shrub to retain its natural shape. If you do shear, cut out farther than you cut last time to avoid bare spots and clusters of cut branches.
Large leafed hedges should be pruned one branch at a time with hand shears. Make your cuts inside the layer of foliage so that they will be hidden, leaving only fresh, uncut leaves on the surface. To avoid hedges with bare leafless bottoms shape your hedge so that the top is narrower than the bottom, letting light to the whole side. Leaves that do not get enough light will drop. Lack of water and nutrients can also cause this. This is especially important on the northern side or on any portion of the hedge that is in the shade of a tree. If your hedge has become bare at the bottom you can cut it back heavily in the spring to stimulate new growth at the bottom, then shape it properly as it regrows. Some shrubs,. however can be killed buy cutting them back too far. If you don’t know how a shrub will respond to a radical pruning, head one branch back to a leafless stub to see how it responds. If the stub sprouts new growth, the shrub can probably be safely cut back.
Hedges that have grown too tall and floppy have usually been allowed to grow too fast. Regular pruning encourages a sturdy structure and will strengthen a mass of wispy stems. Bare spots in a hedge are caused by old age and repeated shearing without allowing the hedge to grow. The problem can be alleviated by cutting away dead twigs, branch by branch and then shearing outside the last cut next time you prune.
I’m designing an open space for a HOA for their housing tract. I’m planning on a central sitting area connected by a series of paths and surrounded by large flat Sonoma fieldstone rocks for sitting. This will be a challenging project as the plants used will not only have to be drought tolerant but will receive no irrigation at all after they are established. The site is browsed by deer so the plants will also need to be deer resistant and gopher resistant. . I think the concept I’ve developed will work and be useful for the residents.