Monarchs & Milkweed: Support Butterflies in San Leandro

Learn how to attract Monarch butterflies to your San Leandro garden with native milkweed, local overwintering sites, volunteer opportunities, and expert planting tips.

How to Support Monarch Butterflies in Your San Leandro Garden

Monarch butterflies are one of nature's most remarkable creatures, traveling thousands of miles each year on wings thinner than a sheet of paper. Right here in San Leandro, you can play a direct role in their survival. The single most powerful thing you can do is plant native milkweed in your garden. Monarchs cannot complete their life cycle without it: it's the only plant their caterpillars will eat, and the only place females will lay their eggs.

This guide covers everything you need to know about attracting Monarch butterflies to your San Leandro garden, from choosing the right milkweed species to discovering local overwintering sites and community resources that make conservation easy and rewarding.

Why San Leandro Is Special for Western Monarchs

San Leandro sits in the heart of the Western Monarch migration corridor. While Eastern Monarchs famously travel to Mexico, Western Monarchs fly to California's coast each fall to overwinter in groves of eucalyptus and Monterey pine. Our city is home to one of the Bay Area's most significant overwintering sites: the eucalyptus grove at Monarch Bay Golf Course, where thousands of butterflies cluster in the trees from late October through February.

When conditions are warm enough, the butterflies spread their wings wide to soak up the sun. On cool days, they hang motionless and look almost like dead leaves. It's an extraordinary sight that very few places in the country can offer. Unfortunately, the Western Monarch population has faced dramatic declines, dropping as low as 2,000 counted butterflies in 2020 before rebounding. The U.S. Fish and Wildlife Service has documented a long-term decline since 2000, making local conservation efforts more urgent than ever.

The good news: your garden genuinely matters. Every patch of native milkweed adds critical breeding habitat along the migration route.

Which Milkweed to Plant in the East Bay

Not all milkweed is created equal. The most important rule for East Bay gardeners: avoid Tropical Milkweed (Asclepias curassavica). It's widely sold at big-box garden centers and looks pretty, but it can disrupt the Monarch migration cycle and increase the risk of a parasitic protozoan that weakens butterflies. Native milkweed goes dormant in fall, which is a natural signal that helps Monarchs know it's time to start migrating. Tropical milkweed doesn't do this.

The two native species recommended for San Leandro and the broader East Bay are:

1. Narrow Leaf Milkweed (Asclepias fascicularis): The most widely available California native milkweed and probably the single most important host plant for Monarchs in the state. It grows 2-3 feet tall with slender, grass-like leaves and clusters of small pinkish-white flowers. It's drought-tolerant, sun-loving, and well-suited to our Mediterranean climate. Plant it in full sun, water well for the first month, then let it largely fend for itself.
2. Showy Milkweed (Asclepias speciosa): Taller and more robust, growing up to 4-5 feet. It has broader leaves and larger, showier flower clusters that are extremely attractive to pollinators. Both species are perennials that die back to the ground in winter and re-emerge in early spring. Don't pull them up thinking they're dead.

You can find both species at Evergreen Nursery in San Leandro and other independent garden centers in the area. One important note from milkweed planting guides: don't plant milkweed within 5 miles of the coast north of Santa Barbara, as these areas are outside milkweed's historical range, and planting too close to overwintering sites can interfere with migration behavior.

Browse ourCalifornia Native Plants collection to find Narrow Leaf and Showy Milkweed in stock.

How to Plant and Care for Native Milkweed

Milkweed has a reputation for being tricky to establish, but once it's in the ground and settled, it's genuinely low-maintenance. Here's what works:

1. Choose a sunny spot. Both Narrow Leaf and Showy Milkweed need full sun for best performance. Part shade works but results in fewer flowers.
2. Plant in well-drained soil. Neither species likes soggy conditions. Amend clay soils with compost before planting if needed.
3. Water regularly for the first 4-6 weeks. After that, both species are quite drought-tolerant. Deep, infrequent watering is better than frequent shallow watering.
4. Leave dead stems standing through winter. Dormant milkweed looks dead, but it isn't. The roots are alive underground. Removing stems too early can disturb overwintering insects and lose valuable nesting material for birds. Orioles are known to use the fibrous stalks for nests.
5. Let it self-seed. If you don't remove the seed pods, Narrow Leaf Milkweed will naturalize and spread gradually. This is a good thing in a butterfly garden.

A newly planted patch of milkweed may not attract Monarchs in its first season, but persistence pays off. Once your plants are established and visible in the local environment, you're far more likely to find eggs and caterpillars the following year.

Check out ourpollinator-friendly plant selection for companion plants that will make your butterfly garden even more welcoming.

Explore Monarch Overwintering Sites Near You

Seeing Monarchs in their overwintering clusters is something people travel across the country for, and it's happening right in our backyard. Here are the key East Bay sites to visit:

1. Monarch Bay Golf Course, San Leandro: The eucalyptus grove here is our local overwintering site. Thousands of Monarchs spend the winter months clustered in the canopy. Best viewed on sunny winter mornings when the butterflies spread their wings to warm up.
2. Ardenwood Historic Farm, Fremont: This East Bay Regional Park regularly hosts overwintering Monarchs in its eucalyptus grove near the historic train tracks. Park staff can point you in the right direction.
3. Albany Hill: A lesser-known but reliable site where Monarchs cluster on the western side of the hill's ridge trail, with documented counts of 400 to 3,000 butterflies.

The Xerces Society's Western Monarch Count project maintains an interactive digital map of overwintering sites across California. It's a great resource for planning a visit and for reporting sightings of your own.

Get Involved: Local Volunteer and Community Opportunities

Planting milkweed in your own garden is a great start, but the San Leandro area has an unusually active community of Monarch butterfly advocates. Getting involved amplifies your impact and connects you with people who share your passion.

San Leandro Butterfly Garden

Located along San Leandro Blvd across from the BART station, beneath the iconic Monarch butterfly mural, this native plant garden serves as a rest stop for migrating Monarchs in spring and fall. Volunteer work parties are held on the first Saturday of every month from 10 am to 12 pm. No experience needed; tools and guidance are provided. You'll learn about native plants firsthand and meet fellow butterfly enthusiasts.

Homegrown Habitats San Leandro (HHSL)

HHSL is a neighborhood-based group working with the City of San Leandro to promote native plant gardening across both private and public landscapes. They maintain a container demo garden at the Manor Branch Library and host free local events throughout the year. Joining their email list is the easiest way to stay connected with what's happening in the local native plant community.

What to Avoid: Common Mistakes That Hurt Monarch Populations

As more gardeners get excited about supporting Monarchs, a few well-intentioned mistakes keep coming up. Here's what to watch out for:

1. Planting Tropical Milkweed (Asclepias curassavica): Widely available and attractive, but it doesn't go dormant, which can confuse Monarchs and prolong their stay in areas where they shouldn't overwinter. It also harbors higher rates of a debilitating parasite called OE. If you already have it growing, cut it back hard in late fall.
2. Using pesticides in your butterfly garden: Even products labeled as 'natural' can harm caterpillars and eggs. If you're growing milkweed for Monarchs, avoid all insecticides in the area, including those targeting aphids. Aphids on milkweed are common but rarely harm established plants, and the insects that eat them (like ladybugs and parasitic wasps) are part of a healthy garden ecosystem.
3. Planting milkweed too close to the coast: As noted above, milkweed planted within overwintering zones can disrupt migration behavior. Follow the Xerces Society guidelines for your specific location.
4. Removing dormant plants in winter: A milkweed plant that looks dead in December is almost certainly just dormant. Mark the spot and leave it alone.

Start Your Monarch Butterfly Garden This Season

San Leandro is genuinely one of the better places in California to support Monarch butterflies. We're close to key overwintering sites, we have an active network of native plant advocates, and our Mediterranean climate suits native milkweed well. You don't need a large garden. Even a single container of Narrow Leaf Milkweed on a patio has been known to attract Monarch eggs.

Start with one or two plants, place them in the sunniest spot you have, and give them time to establish. Once they're settled in, you may find you've become a butterfly person almost by accident.

Visit Evergreen Nursery at 350 San Leandro Blvd to pick upNarrow Leaf Milkweed and get advice from our team. We're open daily 9:30 am to 5:30 pm.

Frequently Asked Questions

1. What is the best milkweed to plant in the Bay Area for Monarch butterflies?

Narrow-leaf milkweed (Asclepias fascicularis) is the top recommendation for the Bay Area. It's a California native, drought-tolerant, and widely considered the most important host plant for Western Monarchs in the state. Showy Milkweed (Asclepias speciosa) is also excellent and grows larger. Avoid non-native Tropical Milkweed, which can disrupt migration and harbor disease.

2. When does milkweed go dormant in California?

Native milkweed in California typically goes dormant in the fall, usually by October or November. The above-ground stems die back, but the root system remains alive underground. New growth emerges again in early spring. This dormancy cycle is actually important for Monarch migration, as it signals butterflies that it's time to head to overwintering sites.

3. Where can I see Monarch butterflies overwintering near San Leandro?

The eucalyptus grove at Monarch Bay Golf Course in San Leandro is the most local overwintering site. Other East Bay options include Ardenwood Historic Farm in Fremont and Albany Hill. The Xerces Society's Western Monarch Count maintains an interactive map of all known overwintering sites in California at westernmonarchcount.org.

4. Can I grow milkweed in a container in San Leandro?

Yes, and it works well. Narrow-leaf milkweed does particularly well in large containers with good drainage and full sun. Use a quality potting mix amended with perlite for drainage. Container plants may need slightly more frequent watering than in-ground plants, especially in summer. A pot of milkweed on a sunny patio can absolutely attract Monarch eggs and caterpillars.

5. Is Tropical Milkweed really harmful to Monarchs?

Conservation organizations, including the Xerces Society and Monarch Joint Venture, recommend against planting it, particularly in California. Because Tropical Milkweed doesn't die back in our mild winters, it can encourage Monarchs to stay in areas where they shouldn't overwinter, disrupting migration. It also tends to harbor higher rates of a parasitic protozoan called Ophryocystis elektroscirrha (OE) that weakens butterflies. Native milkweed is always the better choice.

6. How do I attract Monarchs to my garden besides milkweed?

Adult Monarchs feed on nectar, so pairing milkweed with nectar-rich flowers extends their time in your garden. Good companions include native buckwheat, coyote mint, Mexican sage, and milkweed's frequent companion, goldenrod. Avoiding pesticides entirely in your butterfly garden is also critical, as even organic sprays can harm caterpillars and eggs.

7. How long does it take for Monarch eggs to become butterflies?

The full life cycle from egg to adult butterfly takes roughly 30 days in warm conditions. Eggs hatch in 3-5 days into tiny caterpillars that feed exclusively on milkweed leaves. The caterpillar stage lasts about 2 weeks, followed by a 10-14 day chrysalis stage before the adult butterfly emerges.

8. Where can I volunteer to help Monarch butterflies in San Leandro?

The San Leandro Butterfly Garden holds volunteer work parties on the first Saturday of every month from 10 am to 12 pm. Located along San Leandro Blvd across from the BART station, it's a welcoming spot for anyone interested in native plants and butterfly conservation. Homegrown Habitats San Leandro also organizes free community events throughout the year.

9. Are Monarch butterflies endangered?

The Western Monarch population has been listed as a candidate for Endangered Species protection by the U.S. Fish and Wildlife Service. While counts dropped to alarming lows around 2020, there has been some rebound since. Conservation scientists stress that long-term recovery depends on restoring breeding habitat along migration corridors, which is why backyard milkweed planting matters.

10. Can I grow Showy Milkweed and Narrow Leaf Milkweed together?

Absolutely. Planting both species is actually a good strategy. They bloom at slightly different times and vary in height, which extends the season and adds visual interest. Narrow-leaf milkweed is typically the easier of the two to establish and is more widely available. Showy Milkweed takes a bit more space, but its larger flowers are a magnet for pollinators beyond just Monarchs.