Arizona milkweed is an attractive, native perennial with pine-like leaves that’s an important host plant for queen and monarch butterflies. Here’s everything you need to know about planting and taking care of this Arizona native, including a few important warnings.
Arizona milkweed (Asclepias angustifolia) is a perennial flowering plant that has slender bright green leaves and an overall wispy appearance that makes it a lovely addition to any butterfly garden.
Stems are topped with clusters of white flowers tinged with pink or purple spring through summer. Flowers are followed by seed pods that open to release milkweed floss that disperses the seeds by wind.
This Arizona native is not found in the desert but rather in riparian woodlands, mountains, and canyons. Consequently, it needs more shade and water than many cultivated native plants.
I’ve always found it to be evergreen in Tucson, but it can lose its leaves when grown at higher elevations.
It reseeds readily but not aggressively.
While Arizona milkweed is undoubtedly an attractive plant, it’s mainly grown for being butterfly-friendly.
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. Incredibly, native Arizona milkweed populations in the Huachuca Mountains have been visited by over 500 pollinator species.
Tucson’s native plant nursery, Spadefoot Nursery, says that Arizona milkweed is their #1 selling plant.
Why I Like This Plant
- Attractive pine-like foliage
- Delicately beautiful white and pink-tinged blossoms
- Low-maintenance plant that looks good all year
- Important food source for butterflies and their larvae
Things to Watch Out For
Arizona milkweed is a native riparian species that needs significantly more water than desert-adapted plants. Be prepared to water this plant every 3 days or so.
While many people love the idea of planting milkweed because it’s butterfly-friendly, be aware that milkweeds attract insects of all kinds, including some you might not want to see in your yard, especially aphids and tarantula hawk wasps. While this wasp is not aggressive, its sting is considered one of the most painful of all insect stings.
But if the thought of co-existing with these insects freaks you out, Arizona milkweed is not a good choice for you.
Like all milkweeds, Arizona milkweed is toxic to dogs, cats, horses, and livestock.
Milkweed is potentially dangerous to humans as well as animals. 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 an Arizona 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
Arizona milkweed should be grown in USDA Hardiness Zones 8 to 10. It is tolerant of heat and cold-hardy down to 10℉.
Sun Exposure
Arizona milkweed tolerates full sun, but since it naturally grows in canyons, it prefers part shade. Ideally, plant it where it will be sheltered from the hottest afternoon sun such as on the east side of your house or in the dappled shade under a tree.
Size and Growth Rate
Arizona milkweed is considered a moderately fast grower that will grow faster with more water. It typically reaches a size of 3 feet wide by 2 to 3 feet tall.
Soil
Arizona milkweed prefers clay or silty soils but will grow in any native desert soil, provided it’s well-draining.
Other Location Considerations
Arizona 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.
Arizona Milkweed:
The Essentials
| Common Name | Arizona milkweed |
| Scientific Name | Asclepias angustifolia |
| Origin | Arizona, Mexico |
| Plant Type | Semi-deciduous perennial |
| USDA Zones | Zones 8 – 10 |
| Cold Hardy | To 10℉ |
| Flower Color | White |
| Flower Season | Spring, summer |
| Mature Size | 2-3′ high x 3’ wide |
| Growth Rate | Moderate |
| Sun Tolerance | Part shade |
| Water Needs | Moderate |
| Pests & Diseases | Aphids, root rot |
| Cautions! | Toxic to people, pets, livestock |
| Wildlife | Supports pollinators, especially butterflies 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.
Amending the soil is not recommended. 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 Arizona 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 Arizona Milkweed
Whether you’ve recently planted an Arizona milkweed 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 recommends watering all milkweeds deeply every day for the first week to help the roots get established.
After that, they recommend watering Arizona milkweed every 2 to 3 days.
Should You Fertilize?
The Arizona-Sonora Desert Museum recommends fertilizing Arizona milkweed twice per year during its growing season.
How to Prune
Arizona milkweed maintains a naturally attractive form and doesn’t need pruning. However, if it’s getting leggy or too big for its spot, you can trim in the late fall. But wait until seed pods have formed and released their seeds to give them a chance to reseed.
Insect Pests
When you plant Arizona milkweed, you should expect it to attract insects — that’s the main reason gardeners plant it. But many gardeners are dismayed when their milkweed attracts more aphids than butterflies.
Aphids rarely harm a milkweed plant and, in turn, they attract beneficial insects such as ladybugs and green lacewings.
While you can remove aphids naturally by shooting them with a jet spray of water from your hose, 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 insects and the end result will be more, not fewer, aphids.
Never spray milkweeds with any insecticide (including soap, neem, or Bt).
Spraying can harm butterfly larvae along with insect pests.
Plant Lover Facts
The common name Arizona milkweed suggests that it is found mainly (or only) in Arizona. Ironically, it actually has limited distribution in Arizona, and is only found growing canyons in southeastern Arizona. The majority of native populations are found in Mexico.
Arizona milkweed is not the only native milkweed to grow in Arizona — the general consensus is that at least 29 native species grow in Arizona. And of the 76 native milkweeds that grow in the continental US, 41 can be found in the southwest.
If you live in the desert southwest and want to diversify your butterfly garden, a few other native milkweed species that are commercially available include desert milkweed (Asclepias subulata) and pineleaf milkweed (Asclepias linaria).
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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.
