Saturday, November 7, 2015

Palo blanco: in love with another desert tree

Many of you are familiar with the palo verde, not least because of my obsession with it a few years ago (I did plant three in the front yard). Now I have another “palo” on my mind, this time palo blanco.

While the common names of these two trees are similar—palo verde means “green stick” in Spanish and palo blanco means “white stick”—and both are in the pea family (Fabaceae), they’re not all that closely related. In addition, the common name palo verde is used for several species of Parkinsonia, while palo blanco refers to just one tree: Mariosousa willardiana, an acacia from the Mexican state of Sonora (*).

The first palo blanco I ever saw was at the Desert Botanical Garden in Phoenix, AZ. They have dozens of them throughout the garden. The photo below shows the small cluster in the Ottosen Entry Garden:

141229_Phoenix_DBG_Acacia-willardiana_0001

These are about 12 ft. tall and have a little more to go. The adult size is 15-20 ft.; growth is fairly slow although supplemental water in the summer and fall is said to speed it up.

Here are more photos of the same group. In the bottom two you can clearly see the peeling bark, a hallmark of the palo blanco and for me one of its most striking characteristics.

141229_Phoenix_DBG_Acacia-willardiana_0008  141229_Phoenix_DBG_Acacia-willardiana_0010

141229_Phoenix_DBG_Acacia-willardiana_0006  141229_Phoenix_DBG_Acacia-willardiana_0007

In Northern California, the palo blanco is virtually unknown. Conflicting information about its cold hardiness (and an almost total lack of availability) may have something to with it. Some sources still say the palo blanco is only hardy to 28°F but anecdotal evidence from folks who actually grow it suggests that it’s probably hardy to below 25°F, which is good enough for where we live.

Landscape designers in Southern California and Arizona, on the other hand, are beginning to use the palo blanco more and more. As the design and architecture community Houzz says, “The wispy beauty of the palo blanco tree belies its ability to handle the tough growing conditions of the desert, including areas with reflected heat. [it] is the perfect tree for small, narrow spaces, such as a side yard.”

Here are some more photos of palo blancos from the Desert Botanical Garden:

141229_Phoenix_DBG_Acacia-willardiana_0017

This specimen has reached is mature height.

141229_Phoenix_DBG_Acacia-willardiana_0015  141229_Phoenix_DBG_Acacia-willardiana_0014

It has a striking presence without overwhelming the setting.

141229_Phoenix_DBG_Acacia-willardiana_0016

When I was in Arizona last winter I was looking for a small palo blanco that would fit in my car but all I could find were large boxed specimens. Admittedly I didn’t have a clear idea where I put it in our garden, but I knew I wanted one. But I had to let the idea go—until last month.

That’s when I received one of those droolworthy “Just In” emails from the Ruth Bancroft Garden Nursery:

2015-11-06_14-55-02

There is was, my willowy palo blanco! And with our front yard conversion just around the corner, I knew exactly where it would go: in the middle of what is currently the front lawn. That would also make our project eligible for a Turf Replacement Rebate from the California Department of Water Resources, which requires a tree to planted as part of the turf removal.

This morning I went to the Ruth Bancroft Garden to pick up my palo blanco, and I noticed they had a very nice specimen planted out:

151107_Mariosousa_willardiana_RBG_001

It’s obviously doing well there, which gives me hope that mine will thrive in my front yard.

Here is my specimen:

151107_Mariosousa_willardiana_home_002

It’s dropped some of its leaves, probably because of the time spent in transport (it came from Mountain States Wholesale Nursery in Glendale, Arizona), but they will regrow quickly.

As you can see, the leaves are tiny and they grow at the ends of long phyllodes, essentially modified petioles. They are able to photosynthesize even when there are no leaves on the tree, allowing it to survive long periods of drought.

151107_Mariosousa_willardiana_home_001

It’ll be another month or two before the front lawn is gone and the succulent mound that will replace it has been built, so for now my palo blanco will stay in its nursery container.

divider* For 150 years, the botanical name of the palo blanco was Acacia willardiana. However, in the wake of the 17th International Botanical Congress held in Vienna, Austria in 2005, the genus Acacia underwent a fiercely contested split that is still a hot-button topic in botanical circles. The 1,000+ Australian species (usually referred to as “wattles”) retained the genus name Acacia while the approx. 160 thorny species from Africa, Asia and Latin America became the genus Vachellia, and the remaining 200 species from Africa, Asia and Latin America were split into the genera Senegalia, Mariosousa and Acaciella. For a detailed accounting of these developments, see Kull, C.A. and Rangan, H. (2012). Science, sentiment and territorial chauvinism in the acacia name change debate. In Haberle, S.G. et David, B., Peopled Landscapes: Archaeological and Biogeographic Approaches to Landscapes. Canberra : ANU E-Press. 197-219 (PDF here).

15 comments:

  1. Thank you for the introduction to such a new and interesting plant and giving the details for growing it. However, the best thing in this post are the two photos at the bottom of the quartet near the top. I thought they were watercolors at first and had to enlarge them to check. Superb photography.

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    1. Thank you so much! As you can tell, I'm as passionate about photography as I am about plants and gardening, so this means a lot.

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  2. It's a great looking tree, Gerhard. I wonder if I could get avoid my neighbor's complaints tied to our city's foolish view conservation ordinance if I planted something with wispy foliage like that? I love the peeling bark.

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    1. The palo blanco is the very definition of wispiness. It might work very well for the purposes of your view conservation ordinance. In your climate hardiness would not be an issue.

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  3. I fell in love with the same trees at the desert botanical garden twenty years ago, and scoured sources for them. I finally found a small one gallon (I think I brought it back from Arizona), but it never took off and finally rotted out during winter. I suggest you protect it from frost the first winter, and be sure to plant it on a mound of something well draining, like decomposed granite. Please keep us informed of how your's does, I would love to try it again. Sue

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    1. I think it's harder for a small tree to survive its first winter in a new home than a larger one. At least that's what I'm hoping. The front lawn will be replaced with a succulent mound (or several smaller ones) and I'm planning on planting the palo blanco on top of the mound. In addition, our front yard slopes gently toward the street so drainage shouldn't be an issue.

      If the contorted filbert near your front door ever needs replacing, I think a palo blanco would look awesome there.

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  4. Here you go again, planting a favorite! I'm glad you're giving it a go...the next best thing to having one in my garden is knowing there's one in a friends garden.

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  5. So many drab, narrow, urban spaces could be enlivened by this beautiful tree. Glad you nabbed yours!

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    1. I agree! Do you ever see palo blanco in L.A. area nurseries?

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  6. Loved this tree when I first saw it years ago in Phoenix too! But I'm very sure it wouldn't really like our cooler summers here in the Bay Area. I didn't know they had one at the Bancroft Garden, I suspect they have to protect it from freezes in winter.

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    1. It may need more heat that the Bay Area has to offer, esp. near the water.

      I don't think the specimen at the RBG gets protected. It looks too big for that. If kept reasonably dry, I think it can easily handle 25°F. Typically, frost never lasts for more than, say, 12 hours at a time in Walnut Creek (or here in Davis).

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  7. What a great tree. If we convert our other lawn area I will consider adding this beauty.

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  8. What a great tree. If we convert our other lawn area I will consider adding this beauty.

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  9. I love that tree and am so happy you're planting one. That bark...!

    "Science, sentiment and territorial chauvinism": LOL. It's just as bad with birds, even among us birding peons. I was ready to start a fistfight when the American Ornithologists' Union proposed a split of the Mountain Chickadee into two new species. Sentiment and territorial chauvinism 4EVR ;~)

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