San Diego Native Milkweed Project
Milkweed is the host plant for monarchs. Female butterflies lay their eggs on milkweed leaves, and it is the sole food source of monarch caterpillars. The number of monarch butterflies counted at overwintering sites in California and Mexico has decreased by about 95% since the 1980s! We also are experiencing a major loss of milkweed plants in monarchs’ spring and summer breeding areas, due to factors like urban and agricultural development and the use of herbicides in farming, pastures, and along roadways.
To help conserve this iconic species, we suggest including milkweed in any pollinator habitat planting, and we strongly encourage planting native milkweed instead of tropical or other non-native milkweeds. By native, we mean milkweeds that are found in our region – and San Diego County has several types of native milkweed.
This San Diego Native Milkweed Project is our effort to propagate milkweed native to our area and make it available for purchase at local nurseries or to give away seeds to the public. Local native milkweed was not widely available before we started this project, and most “native” milkweed that was available was from seeds collected mostly from northern California.
We think that seed from the local area will thrive better and be more appropriate for habitat restoration, so we set out in partnership with Partners for Fish & Wildlife and many others to collect seed from wild sources and farm them in our San Diego soil.
We began in fall of 2019, with Narrowleaf Milkweed (Asclepias fascicularis) seed collected from six sites across San Diego County. That seed was planted in late 2019 / early 2020 at four different sites with support from Earth Discovery Institute, Butterfly Farms, Endangered Habitats Conservancy, and Moosa Creek. In year 2, we added Wooly Pod milkweed to the project and seeds for this and Narrowleaf Milkweed were collected from multiple sites in fall of 2020. We also sent seeds to S&S Seeds to be grown at their native seed farm. We are now in year 3 of the San Diego Native Milkweed Project, and have begun to distribute seeds and plants of local native milkweed to the public that have been grown by our partners at S&S Seed, Native West, Moosa Creek, and Anderson’s Seed Co. Special thanks to Eric Anderson of Anderson’s Seed Co. and volunteers at the San Diego Audubon Society for preparing the individual seed packets!
In Fall of 2021, one of our growing partners, S&S Seed Co., harvested 18lbs of Narrowleaf Milkweed seed! These seeds were originally collected from Marine Corps Base Camp Pendleton. This amount is far beyond what we expected, and we are so excited to share it with the public. If you are a backyard enthusiast looking to plant some monarch habitat, we are happy to offer a free packet of seeds. If you are working on a larger scale restoration project, we are happy to discuss larger quantities of seed.
Contact us at pollinators@rcdsandiego.org to get started!
We are so happy that you would like to grow native milkweed for monarch butterflies! This plant can take a little special care and attention to get growing, but once it is established it is a perennial that returns year after year. You will also be rewarded by monarchs visiting throughout the spring and summer. Additionally, you will be one of the people who are helping to make a real conservation difference in the work to keep this butterfly part of our natural world.
Germination Methods
- Cold Stratification: This means that to mimic the cool winter weather, you will chill your seeds in moist soil before planting. To cold stratify seeds, place the seeds into a plastic bag with dampened media such as sand, perlite, vermiculite, paper towel or other media. Make sure media is moist but not too wet, it shouldn’t drip when squeezed. Seal the plastic bag and store it in a standard refrigerator for 4-6 weeks. Seeds should be sown immediately after removing from the fridge. Soil should be kept moist throughout germination period for best results. It's best to get seeds in the ground before end of June for best results.
- Warm Water and Clipping the Seeds: This method takes more equipment and modification of the seed. It uses a warm environment to get the seeds started germinating. To heat shock the seeds, soak them in warm water for 12-24 hours, then drain and repeat this process three times. After the third warm water treatment, place the seeds in a plastic bag wrapped in a warm, damp paper towel for 24 hours before placing into moist soil.
- Direct Sow: Plant the seeds directly into your garden or the place you want them to grow. This method takes less work, but it will be harder to spot the seedlings as they emerge. It might allow the first roots of the seedlings to get better established because you won’t need to transplant them. For direct sowing, prepare the area by removing weeds and amending soil if needed. Seeds can then be scattered onto the soil surface by hand. After scattering, press the seeds 1/4″ into the soil surface with a garden trowel or the soles of your shoes. Seeds can be direct-sown preceding anticipated rainfall in fall to early spring if temperatures are lower and the soil is still moist.
Soil Type
Milkweed generally likes well-drained soil. The Narrowleaf (Asclepias fascicularis) variety can be planted in a native plant soil mix, or even a cactus mix.
General Care of Milkweed
Our native milkweeds are drought tolerant so watering every 1-2 weeks is good for establishing plants but watering requirements are minimal for mature plants. Using a top mulch is recommended to conserve moisture and reduce weed competition.
The plants will go dormant for the winter. Keep the soil cool and moist over the months of December, January, and February. Don’t water them necessarily, but don’t let the soil dry out. Then at the end of February or the beginning of March the plants will reemerge from the soil, re-sprouting from the underground roots. At this time you can begin watering the plants as normal.
You may also see golden aphids on your plants. You will want to remove these aphids by squashing them with your fingers or wetting your fingers with water and washing them off. The main negative thing that the aphids can do is cover your plants with a black residue, which is a dust mixed with the honeydew that the aphids produce.
What if I still have tropical (Asclepias curassavica) milkweed?
In the Fall, at the end of October or beginning of November, please cut the tropical milkweed plants down about 1 inch above the ground.
Monarch Interaction
- When to Expect Them: You can expect to see monarchs on your milkweed plants throughout their breeding season during spring, summer, and early fall.
- What to Expect: Monarch’s rely on milkweeds as their host plant; they are the only plant that adults will lay their eggs on and the only plant that caterpillars can eat. You may see an adult butterfly drinking nectar from flowers or laying their eggs on the bottom of milkweed leaves. Tiny white eggs can be visible on the underside of milkweed leaves. Caterpillars will spend about 2 weeks on milkweed, feeding and growing until they’re ready to form their chrysalis.
- Where Do They Go After Eating Your Plant: Once caterpillars are ready to form their chrysalis, they won’t venture too far from their host plant. Rather, they will seek out a nearby stable structure to hang from and form their chrysalis. This may be a nearby plant or branch but caterpillars might also find themselves on something like an outdoor bench, a fence, pole, or awning.
Monarch Migration
Here in Southern California, we may encounter 2 populations of monarchs. Monarchs born in summer and late fall will migrate south to overwinter in central Mexico or along the California coast. Tens of millions of monarchs overwinter in Mexico’s forest habitats (eastern population) while hundreds of thousands monarchs overwinter in southern California (western population). See here for a map from Monarch Joint Venture showing their amazing trek!
Additional Resources
- Milkweed Care: our leaflet on how to sow and care for milkweed seeds.
- Planting Milkweed: a quick guide on how to plant milkweed.
- Antonio Sanchez of the Santa Monica Mountains Fund made these helpful videos for sowing directly into the ground, or into pots.
- Theodory Payne Foundation's - How to Plant Milkweed
Butterfly Farms: Education and conservation organization and nursery all on one site. Come visit their butterfly free flight house and buy pollinator plants for your garden.
Monarch Joint Venture: A national partnership of federal and state agencies, non-governmental organizations, businesses, and academic programs working together to conserve the monarch butterfly migration.
Monarch Watch: A wealth of information about monarchs – creating habitat, citizen science, migration, biology, and more.
Xerces Society: An organization dedicated to the protection of wildlife through supporting invertebrates. They offer information and resources about issues affecting pollinators and what you can do to help these vital insects, and their website has a section dedicated to conserving the Western Monarch.
- A country-wide monarch monitoring program. Report your monarch sightings and check out their interactive map of sightings so far this year!
- Offers two citizen science opportunities. Help collect data to monitor the status of overwintering monarchs along the California coast by participating in the Western Monarch Count that takes place October - January. You can also contribute to efforts to better understand the breeding habitat of monarchs by entering your monarch and milkweed sightings through the Western Monarch Milkweed Mapper.
RCD Milkweed for Monarchs iNaturalist project:
- Join this project and contribute observations of monarchs in your gardens.
- Check out this overview of monarch citizen science programs.