Newsletter Articles
Butterfly Weed and Milkweed for California Monarchs
By Richard Flowers, ACCNP, Green Thumb Nursery Ventura
Butterfly weed is a milkweed, and milkweed is the one plant monarch caterpillars must have to survive. It is an easy, drought-tolerant plant with bright orange flowers, but for a Southern California monarch garden the best choice is a California-native milkweed such as narrowleaf or showy milkweed, and you should avoid planting tropical milkweed near the coast.
Quick answer: Butterfly weed (Asclepias tuberosa) is a milkweed with orange flowers that hosts monarch caterpillars; it grows in California but is native to the central and eastern United States, not California. For a local monarch garden, plant California natives like narrowleaf milkweed (Asclepias fascicularis) or showy milkweed (Asclepias speciosa), grow them in full sun with well-drained soil, add nectar flowers for the adult butterflies, skip the pesticides, and do not plant tropical milkweed.
| Milkweed | California native? | Notes for a SoCal monarch garden |
|---|---|---|
| Narrowleaf milkweed (A. fascicularis) | Yes | Top native pick; grows in the widest range of conditions |
| Showy milkweed (A. speciosa) | Yes | Native; full sun and well-drained soil |
| Butterfly weed (A. tuberosa) | No (central and eastern US) | A true milkweed that grows here; orange flowers, drought-tolerant |
| Tropical milkweed (A. curassavica) | No | Avoid near the coast; does not die back, can raise parasite levels and disrupt migration |
What Is Butterfly Weed?
Butterfly weed (Asclepias tuberosa) is a species of milkweed and a larval host plant for monarch butterflies, known for its showy clusters of bright orange to yellow-orange flowers.[1] It is easy to grow in average, dry-to-medium, well-drained soil in full sun, and it is drought-tolerant and even does well in poor, dry soils.[1] One honest caveat for local gardeners: butterfly weed is native to the central and eastern United States, not to California, so while it will grow here, it is not a California-native plant.[2]
Milkweed Is the Monarch’s Only Host Plant
Milkweeds are the required host plants for monarch caterpillars, which cannot develop without them. As the conservation groups put it, no milkweed means no monarchs.[3][4] That is why planting milkweed is the single most useful thing a home gardener can do for monarchs. Just remember that the caterpillars eat milkweed while the adult butterflies drink flower nectar to fuel flight, mating, and egg-laying, so a good monarch garden needs both milkweed and a variety of nectar flowers.[3]
The Best Milkweed for Southern California
For a California garden, the best milkweeds are California-native species. The Xerces Society lists 15 milkweeds native to California but recommends narrowleaf milkweed (Asclepias fascicularis) and showy milkweed (Asclepias speciosa) as the top two to plant, because they grow in the widest range of conditions.[4] Both are true California natives: narrowleaf milkweed is native across much of the state,[5] and showy milkweed is native to California and beyond.[6] Butterfly weed will also grow in a SoCal garden and feeds monarchs, but if your goal is to support the local population, start with a native. For more ideas, see our guide to native flowering plants for your SoCal garden.
Avoid Tropical Milkweed Near the Coast
This is the one mistake worth going out of your way to avoid. Tropical milkweed (Asclepias curassavica) is a non-native milkweed that, in mild coastal California, does not die back in winter and can stay green and bloom year-round.[3] That year-round foliage causes two problems: the protozoan parasite OE (Ophryocystis elektroscirrha) builds up to high levels on plants that never die back, exposing each new generation of caterpillars, and the constant presence of milkweed can prompt monarchs to keep breeding instead of migrating and overwintering as they normally would.[7] UC likewise notes that tropical milkweed confuses normal monarch migration patterns.[4] The simple fix is to plant locally native milkweed instead.[3] If you already have tropical milkweed in the ground, cut it down to the ground as winter approaches.[4]
How to Grow Milkweed and Support Monarchs
Milkweed is undemanding. Butterfly weed and the California natives all thrive in full sun, tolerate part shade, and grow in sandy or clay soils as long as the drainage is good, and they are drought-tolerant once established.[1][4] Beyond the milkweed itself, plant a mix of nectar flowers that welcome pollinators so adult monarchs have food through the seasons, and avoid using pesticides on or near your milkweed, since they kill the very caterpillars you are trying to raise.[4] One safety note: milkweed sap can irritate skin and eyes and is toxic if eaten in quantity, so wear gloves when handling it and keep children and pets from nibbling it.[1][8] For more ways to help, see our guide to helping monarch butterflies and other pollinators.
Want to build a monarch garden? Visit any Green Thumb Nursery location and our team can help you find California-native milkweed and the nectar plants that go with it for your part of Southern California.
Butterfly Weed and Milkweed FAQ
What is butterfly weed?
Butterfly weed (Asclepias tuberosa) is a species of milkweed with bright orange flowers that serves as a host plant for monarch caterpillars. It is easy to grow, drought-tolerant, and happiest in full sun with well-drained soil.[1]
Is butterfly weed the same as milkweed?
Butterfly weed is one kind of milkweed. Milkweed is the whole group (genus Asclepias) that monarch caterpillars depend on, and butterfly weed is one species within it.[1]
What milkweed is native to Southern California?
Narrowleaf milkweed (Asclepias fascicularis) and showy milkweed (Asclepias speciosa) are California natives and the two most recommended species for California gardens. Butterfly weed is a milkweed too, but it is native to the central and eastern US, not California.[4]
Is tropical milkweed bad?
In mild coastal California it can be. Tropical milkweed does not die back in winter, which lets the OE parasite build up and can disrupt monarch migration. Plant native milkweed instead, and cut back any tropical milkweed you already have as winter approaches.[7]
How do you grow butterfly weed?
Plant it in full sun in well-drained soil, water to establish it, and then let it be, since it is drought-tolerant. Avoid pesticides, and pair it with nectar flowers for the adult butterflies.[4]
Sources
- [1] NC State Extension, Asclepias tuberosa (Butterfly Weed): plants.ces.ncsu.edu
- [2] Calflora, Asclepias tuberosa: calflora.org
- [3] Xerces Society, Milkweed FAQs: xerces.org
- [4] UC ANR, Save the Monarch Butterfly: Grow California Native Milkweeds: ucanr.edu
- [5] Calflora, Asclepias fascicularis (Narrowleaf Milkweed): calflora.org
- [6] Calflora, Asclepias speciosa (Showy Milkweed): calflora.org
- [7] Xerces Society, Tropical Milkweed: a No-Grow: xerces.org
- [8] ASPCA, Milkweed (Toxic to Pets): aspca.org
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