Desert milkweed is an attractive, succulent-looking native perennial that’s an important host plant for butterflies. Here’s everything you need to know about planting and taking care of this southwest desert native.
If you live in the desert southwest and want to attract butterflies, desert milkweed (Asclepias subulata) is a “must have” native plant.
It is a striking plant that looks more like a succulent than a typical perennial. Its thin, upright, leafless gray-green stems are topped with clusters of creamy yellow flowers from spring through fall.
This plant may look delicate but it’s a tough desert native that thrives in full sun and reflected heat. In its native environment, these plants survive on as little as 3 inches of annual rainfall. It’s unfazed by extreme drought, heat, or cold.
Desert milkweed is about as low-maintenance as a plant can be. Once established it needs only monthly watering. It requires no pruning or fertilizing and produces no litter.
While desert milkweed is undoubtedly an attractive plant, most gardeners plant it to attract and help out our butterflies.
Milkweed leaves are a crucial food source for the larval stage of the queen and monarch butterflies. Milkweed flower nectar is an important food source for butterflies and many other insect pollinators including bees, wasps, and moths.
Why I Like This Plant
- Food source for monarch and queen butterflies
- Extremely low-maintenance
- Long bloom season
- Provides architectural interest all year
Things to Watch Out For
While many people love the idea of planting desert milkweed because it is a butterfly-friendly plant, be aware that it attracts insects of all kinds, including some you might not want to see in your yard, especially aphids and tarantula hawk wasps.
Aphids rarely harm a milkweed plant and they, in turn, attract beneficial insects such as ladybugs and green lacewings.
You may have heard that you can remove aphids naturally by shooting them with a jet spray of water from your hose. But this will not solve your aphid problem because you’ll also blast away the good bugs that keep them under control. The aphids will come back faster than the beneficial bugs. The end result will be more, not fewer, aphids.
Tarantula hawk wasps are also attracted to desert milkweed. While this wasp is not aggressive, its sting is considered one of the most painful of all insect stings.
If the thought of co-existing with either of these insects freaks you out, desert milkweed is not a good choice for you.
Like all milkweeds, desert milkweed is toxic to dogs, cats, horses, and livestock.
Milkweed is potentially dangerous to humans as well. The sap can cause skin and eye irritation. If ingested, it can cause serious digestive and cardiac issues.
Optimal Growing Conditions
If you’re thinking of adding a desert milkweed 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
Desert milkweed should be grown in USDA Hardiness Zones 9 – 11. It’s tolerant of desert heat and is cold-hardy down to 20℉.
Since it has inconspicuous leaves and the stems remain evergreen during the winter, it’s one perennial that appears unchanged during the winter.
Sun Exposure
Desert milkweed tolerates partial shade, but it prefers full sun or even the reflected heat from a nearby wall.
Size and Growth Rate
Desert milkweed is considered a moderate grower which will grow faster with more water. A typical specimen will reach a size of 4’ wide by 4’ tall when mature.
Soil
Desert milkweed is not at all picky about soil provided it’s well-draining. In fact, it performs best when grown in poor rocky, alkaline desert soil.
Other Location Considerations
Desert milkweed should be kept away from children and pets due to its toxicity. It should not be planted where it can easily be brushed against due to its irritating sap.
Some websites recommend using its poolside since it’s virtually litter-free but only if you never have kids over for a swim.
Desert Milkweed:
The Essentials
| Common Name | Desert milkweed |
| Scientific Name | Asclepias subulata |
| Origin | Sonoran, Mojave Deserts |
| Plant Type | Evergreen perennial |
| USDA Zones | Zones 9 – 11 |
| Cold Hardy | To 20℉ |
| Flower Color | Creamy yellow |
| Flower Season | Spring, summer, fall |
| Mature Size | 4′ high x 4’ wide |
| Growth Rate | Moderate |
| Sun Tolerance | Full, part, reflected sun |
| Water Needs | Low |
| Pests & Diseases | Aphids, root rot if overwatered |
| Toxicity | Toxic to people, pets, livestock |
| Wildlife | Nectar attracts butterflies, bees, hummingbirds Food source for butterfly larva Deer, rabbit resistant |
How to Plant
The rule of thumb when planting any milkweed in the desert is to dig a hole twice as wide as the root ball but no deeper. Plant slightly higher than ground level, allowing room for some settling and mulch.
Desert milkweed does not appreciate amended soil. 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 desert milkweed is in the fall. This gives it 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 Desert Milkweed
Whether you’ve recently planted a desert millkweed 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
Once you’ve got your milkweed planted, watering is your most immediate concern.
The Desert Botanical Garden in Phoenix recommends watering milkweeds deeply every day for the first week to help the roots get established. Then water every 4-5 days after that.
Once your desert milkweed is established, water it no more than once per month. If you have typical winter rains, there’s no need to water.
Too much water can cause your desert milkweed to get floppy, develop root rot, and increase its tendency to attract aphids.
Should You Fertilize?
Do not fertilize desert milkweed. Fertilizing will cause this plant to flower less, not more, and will cause the stems to get leggy.
How to Prune
Desert milkweed maintains a naturally attractive form and doesn’t need pruning. However, it’s recommended that you give it a hard “rejuvenating” pruning once every 3 to 5 years. This is best done in the late fall. Your plant should rebound with abundant growth in the spring.
Don’t trim it like a shrub or hedge. This is likely to kill the pruned branches rather than invigorate the plant.
If your desert milkweed gets leggy, it’s either getting too much water, not getting enough sun, or it’s been fertilized.
Don’t Confuse Desert Milkweed With…
Asclepias subulata is not the only plant called “desert milkweed”. Another milkweed, Asclepias erosa, also goes by the same common name. It is a smaller plant (2’ x 2’), has obvious gray-green leaves, and is not as commonly sold as a landscape plant.
Desert Milkweed Cultivar
When you go plant shopping, you may come across a cultivar called ‘Butterfly Magic‘ (Asclepias subulata ‘Butterfly Magic’). This is a natural hybrid discovered by Civano Growers in Tucson. It’s a cross between desert milkweed and whitestem milkweed (Asclepias albicans), which can grow to be 10 feet tall!
As the name implies, this plant attracts butterflies “like magic” but has slightly fuller, sturdier stems than the parent plant.
Fun Fact!
Desert milkweed seeds, which are attached to silky fibers for wind dispersal,
are so incredibly small, it takes over 88,000 seeds to make one pound.
Plant Lover Facts
Desert milkweed (Asclepias subulata) is native to parts of California, Arizona, Nevada, and Baja California, Mexico.
The Native Americans considered desert milkweed a panacea and used it to treat swelling and rashes, and eye, digestive, and respiratory issues. It was also used as a laxative and to induce vomiting.
Desert milkweed uses two interesting adaptations to survive in the desert. Its ephemeral leaves only appear after rainfall. (Ocotillo uses this same strategy.) And since it rarely has leaves, it relies on stems to do the job of photosynthesis. (Palo verde trunk and branches photosynthesize as well.)
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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 over 15 years.
Photo Credit
Stan Shebs, CC BY-SA 3.0, Wikimedia Commons