Mulga is an attractive Australian outback native that’s completely at home in the desert southwest. Here’s how to plant and care for this resilient tree.
Mulga (Acacia aneura), also called mulga acacia, is an evergreen ornamental tree. It has thin silver-gray leaves that almost look like they’re coated with frost. When in bloom, it is blanketed with fuzzy yellow flowers (catkins). The peak bloom time is in the spring, but it also blooms on and off throughout the summer.
This tree is native to the harsh, dry Australian outback, and it’s as tough as you’d expect. Here it thrives in the harshest conditions, such as parking lots and median strips.
But it also makes an attractive addition to any landscape. This low-litter tree is a good choice to put near a pool or patio.
Why I Like This Plant
- Extremely resilient and low maintenance
- Evergreen silver-gray foliage
- Fuzzy yellow flowers throughout spring and summer
- Attracts birds, butterflies, bees
- No thorns, non-toxic
Things to Watch Out For
Mulga wood is hard and brittle. I learned this lesson a few years ago when we had measurable snow in Tucson. The weight of the snow snapped my tree’s trunk. (I loved that tree, and still haven’t gotten over it. 🥹)
Optimal Growing Conditions
If you’re thinking of adding a mulga acacia to your garden, you need to find a suitable place that will keep your tree healthy and looking good… while minimizing maintenance for you.
Here are the key factors to keep in mind.
Temperature
Mulga should be grown in USDA Hardiness Zones 8 – 11. It thrives in extreme heat and survives temperatures down to 15℉.
Sun Exposure
Mulgas are sun-loving and thrive in full sun and even reflected sun, but they can tolerate some light shade.
Size and Growth Rate
Mulga acacia is a slow-to-moderate grower that reaches a mature size of 25’ high by 15’ wide. Unlike many acacias, which only live 20 to 40 years, mulga is relatively long-lived, with a lifespan of around 50 years.
Soil
Mulga ideally prefers acidic-to-neutral soil, but it tolerates our alkaline desert soil provided it’s well-draining. (See Should You Fertilize? below.)
Mulga is so prevalent in parts of Australia
that those regions are known as Mulga Lands.
Mulga Acacia:
The Essentials
| Common Names | Mulga, mulga acacia |
| Scientific Name | Acacia aneura |
| Origin | Australia |
| Plant Type | Evergreen tree |
| USDA Zones | Zones 8 – 11 |
| Cold Hardiness | To 15℉ |
| Flower Color | Yellow |
| Flower Season | Spring, summer |
| Mature Size | 20’ high x 15’ wide |
| Growth Rate | Slow to moderate |
| Sun Tolerance | Full sun, part shade, reflected sun |
| Water Needs | Low |
| Pests & Diseases | Iron chlorosis, root rot |
| Garden Friendly | No thorns, non-toxic |
| Wildlife | Attracts butterflies, hummingbirds, bees Rabbit resistant |
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. As tempting as it is to add amended soil, this is not recommended. Counterintuitively, backfilling with only native soil helps your plant develop a better root system.
When to Plant
The best time to plant mulga 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 Mulga
Whether you’ve recently planted a new mulga 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
As a native of the hot, dry Australian outback, mulgas’ water needs are low, but they still need watering, especially while getting established.
There are two factors to consider when watering any desert tree.
- 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?
Should You Fertilize?
Mulgas generally don’t need fertilizer. But because our desert soils are more alkaline than they prefer, trees can sometimes show signs of iron chlorosis. (Our high pH soil makes iron less available to plants.) If you notice your tree’s leaves turning yellow, feed it iron chelate in the spring.
How to Prune
Mulgas naturally grow as a large shrub or a small multi-trunk tree. Once mature, these trees rarely need pruning.
With the right pruning, a mulga can be trained to grow as a more conventional single-trunk “lollipop” tree. You may need the help of an arborist for this. Note that this will make it more prone to storm damage. (The one I lost to snow was growing this way.)
Plant Lover Facts
Mulgas don’t have leaves — they have phyllodes which are flattened leaf stalks that look and function like leaves. Phyllodes are common in acacias, especially the Australian species.
If you’ve wondered where the name “mulga” comes from, it’s the Aboriginal word “dream seed.” The Indigenous people of Australia put mulga to good use. They used parts of the tree for medicine and food, and used its hard wood to make everyday items including bowls, spears, digging tools, and boomerangs.
Impressively, mulga seedlings 4 inches tall have tap roots nearly 10 feet deep! This is one reason they thrive in the outback. However, don’t expect the same results at home — your nursery-grown mulga will not have a tap root.
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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.
