What is Milkweed and How Do You Care for It?

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What is Milkweed and How Do You Care for It?

Milkweed is the host plant for the monarch butterfly. As a host plant, it provides the monarch larvae and adult butterflies with a food source. Milkweed belongs to the genus Asclepias, which has many different species spread out through America and Mexico. Asclepias line the migration path for these butterflies as they travel back and forth from Mexico to the northern states. It takes multiple generations to make the trip up north and only one generation to make the trip back to Mexico. A trip of that distance is going to require a lot of fuel!

Milkweed can be found in many different variations depending on where it is found. There are many different species native to California such as Narrow-Leaf Milkweed (Asclepias fascicularis), Showy Milkweed (Asclepias speciosa) and Indian Milkweed (Asclepias eriocarpa). There are also many non-native varieties of milkweed that grow well here in southern California. Tropical Milkweed (Asclepias currasavica) has many variations, but is commonly found in red/yellow or yellow.


The parent butterfly will lay its egg on the underside of a milkweed leaf. The egg looks like a little green ball of slime, about the size of a pinhead. The caterpillar emerges immediately hungry. This larvae will eat only the sappy leaves of milkweed. The white milky sap of milkweed contains alkaloids, which cause it to be toxic when ingested.  But Monarch caterpillars are able to ingest this toxin and use it to its advantage.  The alkaloids become present in the body of the caterpillar, making it toxic to predators. Monarch larvae are strikingly colored with yellow, black, and white. The adult is also strongly colored with vibrant orange wings on dark black lines. Larvae or adult, they always present a clear colorful warning to predators. After the caterpillar eats its fill of milkweed leaves, it will wander a short distance to find a safe place to start its chrysalis.


Milkweed is also known to get a few other insect visitors in addition to the butterflies. They will get visited by a true bug called Milkweed Bug. This black and orange bug is relatively harmless to the plant. Milkweed bugs feed on the seed pods, and might hinder your seed production at most. You will probably also encounter orange Oleander aphids on your milkweed and they are also relatively harmless to the plant and caterpillars.

Caring for Milkweed is easy. If you are gardening here in southern California, I’d recommend planting Narrow-Leaf Milkweed (Asclepias fascicularis). It has supported butterflies in our area long before we got here and has the proper alkaloids to keep the caterpillars toxic to predators, while the tropical milkweeds do not provide the same alkaloids. Narrow-leaf Milkweed is drought tolerant, and thrives here. It reseeds itself easily and requires little to no care after the initial planting. Every winter this species will go dormant, and so will the butterflies.


By |2016-08-18T15:31:42+00:00August 18th, 2016|California Friendly Garden Solutions, Gardening|2 Comments

About the Author:

Ron Vanderhoff is a lifelong Southern California gardener and the General Manager and Vice President of Roger’s Gardens. He is a local director of the California Native Plant Society and serves on a number of state and local advisory committees involving horticultural education and natural resource protection. He was a principal contributor to The Butterflies of Orange County and The Wildflowers of Orange County and the Santa Ana Mountains, as well as a special contributor to The Sunset Western Garden Book.


  1. Linda Lee January 31, 2017 at 8:33 pm - Reply

    I live in San Diego with a small backyard.
    1) can I plant milkweed in pots? If so, how big a pot do I need? Or do they need to be planted in the ground?
    2) I purchased 5 tropical milkweed plants from a nursery near me late last year. 3 of them are looking well while the other 2 are not. One of the 2 is actually looking near death. Is this plant going dormant? is this normal? I treat all 5 of them the same.
    3) any recommendation I should buy my milkweed plants next?
    4) I harvested a lot of seeds from those plants. Any germination tips?
    5) how to grow milkweed from cutting?

    • Roger's Gardens February 3, 2017 at 4:43 pm - Reply

      Hi Linda,

      Certainly you can grow milkweed in containers, both the CA native species as well as the South American varieties. The container size should be appropriate for the size and age of the plant. Much like buying new clothes for growing children, in much the same way the container should also be upsized as the milkweed plants grow.
      Yes, tropical milkweeds will look pretty sloppy in the cool winter months. Each plant will behave a bit differently, but I would expect them to lose many of their leaves and essentially stop growing altogether for the next couple of months. Winter is also the time of year when tropical milkweeds should be trimmed down, which will allow them to push out new, fresh growth this coming spring. Trimming your tropical milkweeds down every winter also helps to protect the monarch larvae from contracting harmful diseases that can transfer to the adult butterfly and reduce their vigor.
      Both native and tropical milkweeds grow best in warm weather. I would wait to purchase any additional plants until mid to late spring, when the soil is warm and the days are long. Milkweed is quite difficult to grow from cuttings, which I do not suggest. However, seed is a bit more straightforward and pretty simple. The best time to do this would be about March or even April. Sow the seed in a tray of very fast draining, gritty soil. Cactus Mix blended with an additional 30-50% coarse, gritty sand would be a good mix. The coarsest silica sand that you can find would be good for this. Spread the feathery milkweed seed over the soil surface, then very lightly cover it with no more than 1/4 inch of the same soil mix, 1/8” would be even better. Place this tray in a mostly sunny location, but if the weather is warm and sunny, a bit of very light shade will keep the soil from drying out as quickly and make watering less frequent. It is critical to keep the seeded tray moist during the entire germination period. Depending upon the weather at the time, this watering could certainly be every day, but perhaps less. Germination can be unpredictable, but should take place between one and four weeks from sowing.

      Good luck.


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