Ironwood is a tree that’s as tough as its name implies. It’s an important Sonoran Desert “keystone species” that also makes a beautiful landscape tree, especially when in bloom. Learn how to grow and care for this low-maintenance tree here.
Ironwood (Olneya tesota) is a mostly evergreen tree that has small gray-green leaves and interesting gray bark. It’s two-tone, pea-like flowers range from pink to lavender. When in bloom, this tree is smothered in flowers, giving the ethereal appearance of a smoky pink cloud. Flowers are followed by seed pods that are an important food source for wildlife.
Ironwood makes a beautiful, low-maintenance, long-lived landscape tree. As a Sonoran Desert native, it’s as resilient as you would expect. It’s drought-resistant once established and takes extreme heat and blazing sun in its stride.
It is an important Sonoran Desert keystone species. Amazingly, over 500 species (both plants and animals) find protection under it. It provides food and shelter for wildlife of all kinds, from birds and small mammals to big horn sheep. When in bloom, hummingbirds, butterflies, moths, bees, and other pollinators are attracted to its nectar.
As the largest evergreen tree in the Sonoran Desert, it provides shade for other plants. Here’s a picture of an ironwood acting as a nurse tree to a saguaro cactus. Saguaros often grow in the shade of trees that protect them from intense sun, temperature extremes, and from getting trampled when they are small.
Why I Like This Plant
- Lovely pastel flowers
- Low-maintenance, low litter
- Long-lived keystone species
- Beneficial to wildlife of all kinds
Things to Watch Out For
These trees naturally grow slowly, so they aren’t going to provide you with shade fast. You can speed up their growth with irrigation, but be aware that trees that are irrigated produce copious numbers of suckers that need to be pruned.
Unlike most flowering trees, ironwood does not reliably bloom every year. It only blooms when the right conditions have been met. Its blooms usually coincide with mild, wet winters.
It’s semi-deciduous, meaning it’s largely evergreen, but will lose its leaves during either extreme cold or drought.
The bark of young ironwood trees is lined with pairs of sharp thorns. As trees mature, these go away.
Optimal Growing Conditions
If you’re thinking of adding an ironwood 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
Ironwood should be grown in USDA Hardiness Zones 9 – 11. It thrives in extreme heat, but is not equally tolerant of cold. Mature plants are hardy down to around 20℉ while young trees are hardy to 25℉. Trees lose their leaves during extreme cold. It’s generally recommended that young trees be protected from frost.
Sun Exposure
Ironwood is perfectly happy in full sun or reflected heat.
Size and Growth Rate
In the wild, ironwood is a slow growing tree, but you can speed up its growth with supplemental water. A typical mature specimen is 25 to 30 feet tall and wide.
Soil
Ironwood will grow in almost any desert soil, provided it’s well-draining. In its native habitat, it grows along sandy dry washes or on rocky slopes
Ironwood:
The Essentials
| Common Name | Ironwood |
| Scientific Name | Olneya tesota |
| Origin | Sonoran Desert |
| Plant Type | Semi-deciduous tree |
| USDA Zones | 9 – 11 |
| Cold Hardiness | To 20℉ |
| Flower Color | Pink, lavender |
| Flower Season | Spring |
| Mature Size | 30’ high x 30’ wide |
| Growth Rate | Slow |
| Sun Tolerance | Full, reflected sun |
| Water Needs | Low |
| Pests/Diseases | Desert mistletoe |
| Cautions | Thorns |
| Wildlife | Attracts pollinators, birds, mammals |
How to Plant
The rule of thumb when planting any 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 ironwood 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 Ironwood
Whether you’ve recently planted a new ironwood 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 ironwood in the ground, watering is your most immediate concern. Here is a 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
Trees can survive on as little as 3 inches of rain per year, but don’t expect much growth if you try to grow yours on rainfall alone.
Once your tree is established, water once or twice per month during summer and not at all during the winter.
Trees will lose their leaves during drought, as a survival mechanism. Don’t freak out if this happens to yours, but consider it a sign that it could use more water.
Should You Fertilize?
There is no need to fertilize ironwood which evolved to grow in desert soil. And as a member of the legume family (Fabaceae), it fixes nitrogen, which naturally improves the surrounding soil.
How to Prune
Ironwood typically is naturally a multi-trunk tree and should be grown as such. It should be minimally pruned, this is not a tree to turn into a lollipop. If your tree needs shaping, I urge you to hire a certified arborist (NOT a landscaper) to prune it.
Trees that are irrigated produce lots of suckers. You should remove those as soon as you notice them. Pinch them with your fingers to prevent scarring of the trunk.
Plant Lover Facts
Ironwood (Olneya tesota) also goes by the common names desert ironwood and tesota. It is the only member of its genus. There are over 200 plants that go by the common name “ironwood” (or a variation of). That’s why knowing a plant’s scientific name can be important!
Its native range includes Arizona, California, and northwest Mexico, including the Baja Peninsula.
Ironwood has had many traditional uses. The wood is extremely hard and is so heavy, it sinks. It was used as firewood and to make tools and building materials. Its roasted pods and seeds were consumed as porridge, flour, or cakes.
Now ironwood wood is prized for its woodworking qualities. You may have seen (or own) ironwood carvings which are usually of animals found in the southwest.
Did you enjoy this article?
Sign up for our weekly newsletter
where you’ll find more great info on creating &
maintaining a beautiful, carefree desert landscape.
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 over 15 years.
Photo Credits
Matt Lavin, CC BY-SA 2.0, Wikimedia Commons