Growing Milkweeds in SF for The Monarch Butterfly

Today many people are concerned about our butterfly populations and particularly the western Monarch.   Overwhelming use of herbicides has decimated the milkweed, the Monarch butterfly sole food source.  Once in the millions, now down in the thousands.  

I was asked to plant some milkweed in my Noe Valley garden to help support the Monarch butterfly.  I recalled reading that some species of milkweed are not appropriate to plant in our area.  So I had to do some research and here's what I found.  I was looking for milkweeds that grow here and are easily available from local nurseries.

Asclepias incarnata (Swamp Weed), two cultivars available at Digging Dog Nursery in Mendocino. 

Going by its common name, this plant likes moisture.  Something that is not readily available in our California climate.  Only for the very few moist areas in San Francisco.

Asclepius curassavica (Tropical Milkweed) - Available at Annie’s.  I have read not to plant the tropical milkweed due to a parasite that may reside on the milkweed and cause disease in the larvae that chew on it.   A protozoan parasite of monarch butterflies should be controlled by cutting back in fall to remove the protozoan from infecting next year’s butterfly. Cut back your Asclepias currasavica in late Fall.  I'm all for coppicing perennials in my gardens.

Lady Beetle on Tropical Milkweed

Asclepius tuberosa (Butterfly Weed), available at Diiging Dog nursery although it is currently sold out for 2022. 

I have also seen this available at Flowercraft in San Francisco on Bay Shore Blvd.  This seems to be the one.  Pictured below in my Potrero Hill garden a few years ago.  Unfortunately I never once saw a butterfly or larvae on the plants.  

Asclepias speciosa (Showy Milkweed), available at Annie’s in Richmond.

Seeds available at Larner Seeds  

Seeds also available at American Meadows.

And Select Seeds.

Showy Milkweed is by far the most interesting and beautiful.  Pictured below from a community garden near my Eureka Valley garden.  I collected seeds and will try to germinate them for the fall.

Other interesting options and will try a few over the next year or so.  

Asclepias physocarpa, “Family Jewels Tree”, available at Annie’s 

Asclepius eriocarpa (Indian Milkweed) - Seeds available at Larner Seeds  

Coastal gardeners should think twice before planting milkweeds, which may not have grown there historically. It can create problems to draw migratory species out of their regular patterns. For example, some species may not have resistance to the fungi stimulated by fog. The caterpillars that will develop on that plant may not survive, thereby "wasting" the eggs of that species. Though monarchs may overwinter along the coast, they breed inland, and it is here that restoring milkweed can be most effective. - From Larner Seeds website.

Asclepia fasicularis (Narrow-leaf Milkweed), available at Annie’s. 

Asclepia fruticosus (Gomphocarpus) Emersia grows this in Sonoma County  

Asclepia vestita (Woolly Milkweed)

Asclepias californica - look for seed source.

Asclepia subulata (Ajamete, Rush Milkweed, Desert Milkweed)

Read more about milkweeds at Pacific Horticulture -->