One of the earliest trees to bloom here in the Santa Clara Valley is the acacia. Actually, I should be more specific, as there are hundreds of trees and shrubs in the
Acacia genus, and not all of them closely resemble one another. Specifically, we have the Bailey acacia (
Acacia baileyana), also called Cootamundra Wattle or Golden Mimosa Tree.

The Bailey acacias start producing fragrant cascades of little yellow "pompom" flowers in January, and this year was no different. However,
this year, I was determined to get a good photo of one in bloom! And I did -- in
Los Gatos, where they seem to be especially common. (Click the photo above for an up-close-and-personal view of the foliage and flowers.)
I remember someone once called the Bailey acacia "an outlaw tree" because it grows so fast, both from seeds and from suckers, that a few trees can overrun an area. Between that, and the fact that acacias grow well even under rather poor conditions, the complainer probably thought the behavior was too similar to that of
weeds! I think he/she also found the trees unattractive except when in bloom.
I don't agree with any of this. There are plenty of dry, exposed embankments, hillsides and abandoned areas that would be ugly and barren -- not to mention subject to erosion -- without trees like the acacia, which can also grow as large multi-trunked "shrub-trees." They grow fast, are drought tolerant and are rarely bothered by pests; sounds good to me! (These attributes also describe
Tree of Heaven,
Ailanthus altissima, which truly is considered an invasive "weed tree," although even it is not without its merits. It's also the title character of Betty Smith's classic 1943 novel,
A Tree Grows in Brooklyn.)
At any rate, Bailey acacia blossoms are one of the most cheerful shades of yellow I've seen, and I generally don't even care for yellow. You can spot an acacia from far away when it's blooming, not only from the bright color but also from the profuse, cascading nature of the "puffballs." Even when it's done blooming, it's interesting: the foliage is a blue-gray-green color and has a delicate feathery shape like that of the
mimosa or silk tree,
Albizia julibrissin. (It's no surprise, as the two trees are in the same family:
Fabaceae, formerly called
Leguminosae. Some people say the trees are in the
Mimosaceae family, but I use the most current
Sunset Western Garden Book as my authority.)
It's unfortunate that most members of the
Acacia genus live only 20 to 40 years on average, but their fast growth, hardy nature and beautiful blossoms are the trade-off. I would even go as far as to consider the acacia something of a "nurse tree." This term is typically used for fast-growing, short-lived trees planted near or around the sapling trees you actually desire.
The "nurses" help stabilize the soil, control weeds and reduce wind. Some nurse trees, strategically planted, can also provide just the right amount of shade on the foliage and trunks of tender young saplings that might otherwise suffer from sunscald or burn. Acacias have another nurse-like benefit: as with many leguminous trees, their root nodules contain nitrogen-fixing bacteria that actually help enrich the soil.
Alders, incidentally, also make good nurse trees, for all of the reasons above. (
White alder,
alnus rhombifolia, is among the most common and fastest growing, and is very tolerant of heat and wind). Alders also have the nitrogen-fixing effect, although they are not in the legume family. They do require significantly more water than most nurse trees, however; when alders are used in landscaping, they need good irrigation!
And now the acacia attribute everyone has been waiting for me to address:
the allergy issue! Yes, I do agree with the tree's detractors about that. Apparently the pollen causes nasal allergy symptoms and asthma flare-ups in more than a few people. For some, it even causes a skin rash.
I have mild asthma and allergies myself, so I empathize with what it's like to be uncomfortable and irritated by an allergen. However, I have no problem with acacias. But you probably already figured that out, seeing as I was surrounded by them when taking my photos!