Palo blanco is a unique desert tree with white bark and draping willow-like leaves. It’s perfect for protected, narrow spaces in your garden. Here’s everything you need to know about planting and caring for this Sonoran Desert native.
Palo blanco (Mariosousa willardiana) is a medium size shade tree. Its name means “white stick” — its papery white bark is one of this tree’s most arresting features. Palo blanco has long, narrow, shoestring-like leaves, and when mature, the overall effect is graceful and draping, reminiscent of a small weeping willow.
But this tree is nothing like a typical water-thirsty willow. It’s a tough Sonoran Desert plant that survives in hot sun and with little water.
It’s not terribly cold-tolerant and usually loses its leaves during the winter in much of the desert southwest.
Since this tree only gets about 10 feet wide, it’s the perfect size for small yards or narrow spaces.
Palo blanco is an excellent tree for attracting hummingbirds and butterflies. Hummingbirds love to perch in the branches and often use small strips of bark for building their nests.
In the spring, cream-colored flowers that resemble fuzzy caterpillars provide a nectar source for butterflies. The leaves are a larval host for several species of butterflies and moths.
Why I Like This Plant
- Narrow profile makes it a good tree for small spaces
- Eye-catching white, papery bark
- Provides pleasant dappled shade
- Is a magnet for hummingbirds and butterflies
Things to Watch Out For
This is not a tree if you are looking for instant gratification — it takes about 10 years to go from a spindly sapling to a mature, graceful tree.
In many areas, it’s borderline cold tolerant. It almost always loses its leaves in the fall and sheds bark, so it can be messy.
Optimal Growing Conditions
If you’re thinking of adding a palo blanco to your garden, you need to find a suitable place that will keep your plant healthy and looking good… while minimizing maintenance for you.
Here are the key factors to keep in mind.
Temperature
Palo blanco should be grown in USDA Hardiness Zones 9 – 11. It has no problem handling extreme heat, but cold can be a limiting factor.
According to the Arizona-Sonora Desert Museum, it can survive down to 15℉, but mature trees will suffer damage at 20℉ and young trees at 26℉.
In case of a severe cold snap, they recommend protecting the trunk with a hot water heater blanket or some other kind of protective wrap. Clearly, this is not something everyone will be willing or able to do!
Sun Exposure
Palo blanco thrives in full sun and doesn’t mind reflected heat. This makes it a good choice for small spaces with walls such as courtyards or patios.
Size and Growth Rate
Palo Blancos grow slowly and are taller than wide, ultimately reaching a height of 20 feet and a width of 10 to 15 feet.
Soil
Palo blanco grows well in poor, rocky, or sandy desert soil that is well-drained.
Other Location Considerations
Since it’s non-toxic and unarmed (no thorns, spikes, or prickers), you can feel comfortable placing it near a sidewalk, patio, or anywhere it might come in contact with pets and people.
But don’t plant near a pool or anywhere else you mind some plant debris.
Palo Blanco:
The Essentials
| Common Names | Palo blanco, white bark acacia |
| Scientific Name | Mariosousa willardiana |
| Southwest Native | Mexico |
| Plant Type | Semi-deciduous tree |
| USDA Zones | Zones 9 – 11 |
| Cold Hardiness | To 25℉ |
| Flower Color | Cream |
| Flower Season | Spring |
| Growth Rate | Slow to moderate |
| Mature Size | 20’ high x 15’ wide |
| Sun Tolerance | Full, reflected sun |
| Water Needs | Low |
| Pests & Diseases | None |
| Garden Friendly | No thorns, non-toxic |
| Wildlife | Attracts butterflies, hummingbirds |
How to Plant
The rule of thumb when planting any shrub or tree in the desert is to dig a hole three times as wide as the root ball but no deeper. Amending the soil is not recommended. Counterintuitively, backfilling with the same native soil you just dug up helps your plant develop a stronger root system.
When to Plant
The best time to plant palo blanco is in the fall. This gives your tree three seasons to grow roots and get established before the following summer.
The second best time is in spring, the earlier the better. This still gives your plant time to get established before the intense heat of June arrives.
How to Care for Palo Blanco
Whether you’ve recently planted a new palo blanco or have an existing one in your yard, here’s how to take care of it to keep it healthy and looking its best.
How to Water New Plants
Once you’ve got your palo blanco in the ground, watering is your most immediate concern. Here is the recommended watering schedule for new trees planted in the spring or fall.
| Weeks 1 & 2 | Every 3 – 4 days |
| Weeks 3 & 4 | Every 6 – 7 days |
| Weeks 5 & 6 | Every 7 – 10 days |
| Weeks 7 & 8 | Every 10 -14 days |
After week 8, gradually extend the time between waterings.
How to Water Established Plants
As your tree becomes established, there are two watering factors to consider.
- First is how often to water. This will vary with the seasons.
- Second is how much water to give your tree with each watering. This depends on its current size.
To determine the ideal watering schedule for any desert tree, you’ll find everything you need to know, including easy-to-use charts, at How to Water Desert Trees: How Often? How Much?
Note that palo blanco needs little to no water once established, although supplemental water in summer and early fall will encourage growth and canopy density.
Should You Fertilize?
There is no need to fertilize palo blanco. They get all the nutrients they need from desert native soil. And since they are a member of the legume family (Fabaceae) they fix nitrogen which naturally improves their surrounding soil.
How to Prune
Like most desert trees, palo blanco ‘s natural shape is a multi-trunk tree. However, it is usually grown as a single-trunk tree with a weeping willow-like look. To achieve this, you’ll need to train the tree while young.
If you are at all unsure about how to go about this, I strongly urge you to hire a professional. Hiring an arborist (not a so-called “landscaper”) to get your tree off to the right start is an excellent investment that will result in a beautiful tree that will grace your yard for decades to come.
Once mature, it needs little or no pruning.
Don’t Confuse Palo Blanco With…
There are a few other trees that go by the common name palo blanco.
Sugar Hackberry (Celtis laevigata) is a common tree in Texas that goes by many names, including palo blanco. Once you’ve seen one you should have little difficulty telling them apart. While it does have white papery bark, it’s a huge tree — up to 80 feet — and has broad green leaves.
Lysiloma candida is another tree that’s called palo blanco. It grows only on Mexico’s Baja Peninsula. I’ve never seen one for sale, so there’s little chance you’ll pick one up by mistake.
Plant Lover Facts
Palo blanco is native to northwestern Mexico but has naturalized in Arizona.
Palo blanco wood was often used by the Seri Indians for building material because of its characteristically straight and minimally branched trunk. Traditionally, it was used to make baskets and bows.
The Acacia genus has been in flux due to new DNA evidence. Now it is more narrowly defined to plants found in Australia. Acacias native to the desert southwest have been reclassified as belonging to the Mariosousa genus, a small group of only 13 species.
Palo blanco’s most current botanical name is Mariosousa willardiana but it is still often referred to as Acacia willardiana.
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for 15 years.
