We live in Westlake Village where many white birch trees, including ours, have died. When we remove them, can we replace them with other birches or do we need to use a different tree? If so, what type do you suggest that is about the same size? Also, do we need to do anything with the soil before planting or wait a certain length of time before planting a new one? — Ken Erhard
As the drought persists, I have received an increasing number of laments regarding dying birch trees. For years, it was a convention of front yard Los Angeles landscaping to build a mound of earth upon which birch trees would be planted. To complete the effect, boulders would be placed in front of the mound. This was in the days when everyone had a lawn, which grew over the mound of earth, too, since the birch tree’s need for regular water matches that of a lawn.
No tree is less suited to water rationing than the birch. In Westlake Village, irrigation with conventional spray and rotary sprinkler is limited to two days a week, not enough to keep a birch tree alive in a heat wave. However, this limitation does not include drip irrigation. Therefore, you could replace your dying trees with other birches and not concern yourself with water rationing limitations as long as you installed a drip system prior to planting them.
Drip irrigation has come a long way since the early days when you had to punch holes in black polyethylene lines to accommodate emitters, spaghetti tubing, or mini-sprinklers. Today, brown Netafim drip tubing contains in-line emitters, spaced 12 or 18 inches apart, so all you need to do is roll out the tubing wherever you wish to plant — or where you have already planted. Just be sure that you separate valves and water lines according to plant type so that trees and annuals, for example, do not share the same irrigation line since their water requirements differ significantly. And, for further water savings, don’t forget to lay down at least three inches of mulch which will conveniently cover your drip tubing (if you find it unsightly), too.
While you can replace a birch with a birch, there are other trees you might consider. Medium-sized citrus trees such as ‘Eureka’ lemon, ‘Oroblanco’ grapefruit, and ‘Fremont’ tangerine have an evergreen growth habit and fragrant flowers, as well as providing fruit and juice for months on end. As a matter of fact, many fruit trees of modest stature, from ‘Anna’ and ‘Dorsett Golden’ apple to many varieties of guava and fig to Chinese date (Zizyphus jujube) and other exotic species would grow well in Westlake Village. There is a wide assortment of fruit trees available through growers such as Papaya Tree Nursery in Granada Hills, Otto & Sons Nursery in Fillmore, and La Verne Nursery in Piru.
For fragrant flowers on an evergreen ornamental tree, think about planting a dwarf magnolia such as ‘Little Gem’ which reaches only 20 feet in height. Champaca (Magnolia/Michelia champaca), a large shrub or small tree that is also 20 feet tall at maturity, has intensely fragrant yellow-orange flowers. There are several species of Melaleuca trees, drought tolerant and showing off unusual flowers and exfoliating bark, that would also be appropriate choices, as would Arbutus ‘Marina,’ with pink urn-shaped flowers and cinnamon bark. Catalina ironwood (Lyonothamnus floribundus), with distinctively toothed foliage and peeling bronze bark, is a widely admired California native selection.
As far as soil preparation for planting is concerned, you would want to remove the remnants of your birch trees, including all roots, since you want the ground to be free of debris that could interfere with the root balls of your new trees. Select trees growing in 15 gallon size containers or larger and you will not have to amend the soil. Studies have shown that trees in such large containers, at a minimum height of 6 feet, will more readily adapt or acclimate to their new surroundings when the existing soil is left as is. Amending the soil could delay the acclimation process and permanently stunt the growth of the tree. No wait time between removal of dead trees and planting of new ones is necessary.
Speaking of drip irrigation, Rain Bird Corporation has developed a subsurface drip irrigation (SDI) system that makes it possible to have a lawn while conserving water . With this system, there is a 70% savings in water use as compared to above ground lawn irrigation. The biggest obstacle to subsurface irrigation has been emitters clogging due to growth of grass roots that block the emitters. An initial solution to this problem, utilized by Toro Corporation, was provided by mixing a pre-emergent weed control chemical together with the plastic polymers specified in manufacture of the emitters. Roots simply do not grow into herbicide laden plastic emitters. With the Rain Bird SDI system, a copper band inside the tubing releases ions that bind to grass root tips (positive copper ions or cations bind with negative ions or anions that naturally cover roots), blunting the root tips and halting their growth.
SDI has been used in commercial crop production, inclduing sugar cane, corn, tomato, and lettuce acreages, and is especially attractive where water supply and water quality are problematic. Water savings are huge since water lost through wind and, especially, evaporation from the soil surface are no longer an issue. In addition, recycled sewage water can be applied without safety concerns when delivered below the soil surface. SDI is not only appropriate for lawns and vegetable beds but for drought tolerant gardens, too. Close to home, the city of Sierra Madre installed SDI when it relandscaped City Hall with California native and drought tolerant plants. Just as drone delivered packages and driverless cars may soon be the norm, so too, perhaps, will subsurface irrigation become the standard technology when it comes to watering your garden.