January Tree of the Month: Winter-Blooming Acacia Trees
By David Gress
In January and February in Santa Barbara, the first trees to present amazing canopies of color are the Acacias. The most remarkable of these are three species that seem to explode with bright-yellow flowers: Bailey Acacia; Silver Wattle Acacia; and Green Wattle Acacia.
Out of the dozens of other Acacia species in our area, these three stand out as the earliest of winter bloomers - and the ones that bear the most profuse floral displays. Besides flowering beautifully, they are evergreen and well suited to our Mediterranean climate.
All three have similar, small (¼ inch), rounded, yellow flowers, which occur in racemes or panicles that develop at the ends of the branches and contain 25 to 30 flowers. The flowers have a delightfully sweet scent, something like fresh cotton candy. Fair warning: Some people develop allergic hay fever to the voluminous pollen that drifts off in the wind.
The most ornamental is Bailey Acacia, which has been a popular tree here since it was first introduced in 1903 by the pioneering horticulturist, Dr. Francesco Franceschi. In our area, it grows rapidly to form a small-scale tree (20- to 30-feet tall and 20- to 35-feet wide) with a broad, rounded crown.
Its gracefully weeping branches are covered with silvery blue-gray foliage. The bipinnately compound leaves are comprised of 2 to 6 pairs of pinnae each bearing 12 to 30 pairs of pinnules (3/16-inches long), which create a delicate fern-like appearance. After pollination, the flowers produce bean-like seed pods (2- to 4-inches long and ¼- to ½-inches wide). Its bark is light gray; smooth when young but developing furrows with age.
It grows naturally as either a multiple-trunked tree or a large shrub. It can be trained as a single-trunked tree, good to plant as an individual specimen or in mass plantings for a screen. It does best in full sun and will thrive in any type of soil, provided it is well-drained. It is fairly drought-tolerant and is cold-hardy to 20 degrees F. It can survive with our normal rainfall but, understandably, does better with some additional irrigation during the dry season.
The Bailey Acacia is also known by other common names: “Fernleaf Acacia”; “Golden Mimosa”; and, “Cootamundra Wattle”. Its botanical name is Acacia baileyana. The genus name, “Acacia”, is Latin but was derived from the Greek word, “akakia”, meaning “Egyptian thorn acacia”. The specific epithet, “baileyana”, honors the Australian botanist, Frederick Mason Bailey (1827-1915).
It is native to a limited area of the Cootamundra region of New South Wales, Australia, where it is known as Cootamundra Wattle. The word “wattle” comes from an old English word for the branches and twigs that were used in weaving lattice for sheep fences and other structures. In Australia, early European settlers made huts and shelters of wattle, using the long flexible branches of Acacias mixed with mud. On that continent, the term became synonymous with Acacia trees and the name stuck, well, like mud.
There is a purple-leafed cultivar, Acacia baileyana ‘Purpurea’. Its leaves emerge with a distinctive lavender to almost purple color that turns silver-gray with age. It is a shorter tree, with a maximum height of 20-feet.
The other two species, the Silver Wattle Acacia and Green Wattle Acacia, are quite similar to each other, differing primarily in their leaf colors. They both differ from Bailey Acacia in their taller upright growth habit (up to 50-feet tall with a spread of 40-feet) and in their relatively larger leaves. Their bipinnately compound leaves have 20 to 50 pairs of pinnules on rachis up to 4-inches long, with 10 to 26 pairs of pinnae. These species occur naturally in southeastern Australia, with the Silver Wattle’s range extending further into Tasmania. They naturally hybridize together and also naturally hybridize with the Black Wattle (Acacia mearnsii), making their exact identification rather difficult.
The Silver Wattle, also known by the common names “Blue Wattle” and “Mimosa”, has the botanical name, Acacia dealbata. The specific epithet, “dealbata”, is from the Latin word, “dealbatus”, meaning “whitewashed”.
The Green Wattle has the botanical name, Acacia decurrens. The specific epithet, “decurrens”, is derived from a combination of the Latin words, “de” and “curro”, meaning “running down the stems”. The Green Wattle also differs from the other two species in that it has dark gray bark that frequently develops warts along the trunk.
In Australia, Acacias are used in numerous ways: for their wood - to make furniture, tools, and fine carpentry; for their flowers - to make dyes, food additives, and floral arrangements; and, for their sap - to formulate chemicals for medicines.
Unfortunately, these Acacias, like many other Acacias, are short-lived, having an expected life span of 30 to 40 years. Fortunately, they are easy to grow and appear to be free of pests and diseases. They are known to be invasive in some Mediterranean regions; locally, they do not appear to be a pest tree problem. As a precaution, planting should be limited to managed urban landscapes. These trees are essentially maintenance-free; however, periodic pruning to lighten the load of branches is well advised, since their wood is brittle and can break in winds and rain.
In the right location, any of these lovely Acacias will make a stunning addition to a residential, commercial, or park landscape. Soon enough, their spectacular yellow blooms will be easy to spot around town!
Bailey Acacias are seen on the 2200 block of Alameda Padre Serra, on the 1800 block of Eucalyptus Hill Road, at 1 S. Los Carneros Road, and on the 101 Freeway at the State Street/ Highway 154 overpass, as well as scattered around in the Mission Canyon neighborhood. Silver Wattle Acacias and Green Wattle Acacias are seen on Old Coast Highway (between Park Place and Hot Springs Road), on the 100 to 200 Blocks of Hot Springs Road (along with Black Wattles), and on the 600 Block of Cold Spring Road.
Tree-of-the-Month articles are sponsored by Santa Barbara Beautiful, whose many missions include the increase of public awareness and appreciation of Santa Barbara’s many outstanding trees and, in a long-time partnership with the City Parks & Recreation Department, the funding and planting of trees along the City’s streets.
Those who wish to honor a special someone can do so with an attractive commemorative marker that will be installed at the base of an existing street tree in the City of Santa Barbara. Because Santa Barbara Beautiful has participated in the planting to date of over 13,000 street trees, there are plenty of trees from which to choose! Application forms are available on the Santa Barbara Beautiful website, www.sbbeautiful.org.
Article and Photos by David Gress