6 minute read
Planting for Monarchs: A Garden Guide to Recovery
By Sarah Cusser, Ph.D., Terrestrial Invertebrate Conservation Ecologist, and Stephanie Clark, Ph.D., Applied Ecologist
Each fall, the arrival of western monarch butterflies (Danaus plexippus) back to California’s coast from their migration marks a moment of quiet wonder. Clusters of orange and black wings cling to cypress (Family Cupressaceae), pine (Family Pinaceae), and other coastal trees, where the butterflies will rest and conserve energy for winter. These overwintering gatherings, once numbering in the hundreds of thousands, have declined in recent decades, and with them, a part of our region’s ecological and cultural heritage.
The Status of Monarchs in Central California
Western monarch populations peaked in the late 20th century, particularly in the 1980s. At that time, over four million monarch butterflies overwintered at hundreds of coastal sites from Mendocino to San Diego. Today, their numbers have plummeted. The annual Western Monarch Thanksgiving Count, coordinated by the Xerces Society and partners, documented fewer than 2,000 individuals in 2020, a decline of 99.4% since the 1980s. Since then, the population has rebounded modestly, reaching nearly 230,000 butterflies in 2023. While this increase is encouraging, monarch populations remain dangerously unstable and vulnerable to extreme weather, habitat loss, and disrupted migratory cues linked to climate change.
Central California, including Santa Barbara County, remains critical to the monarch’s overwintering strategy. Sites like the Goleta Butterfly Grove at Ellwood Mesa Open Space, the Monarch Butterfly Grove at Pismo State Beach, and scattered groves along the Gaviota Coast serve as essential refuges. Yet many of these habitats are threatened by tree senescence*, development pressure, climate change, insecticide use, and altered microclimates.
*Senescence is just a fancy word for aging. It describes the gradual process where living things, like animals, plants, or even single cells, wear out and become less functional over time.
Planting the Right Milkweed at the Right Time
Monarchs depend exclusively on milkweed (Asclepias spp.) as the host plant for their caterpillars. However, not all milkweed is equally beneficial, particularly in California’s Mediterranean climate. A common yet problematic choice is nonnative tropical milkweed (A. curassavica), often found in garden centers and local hardware stores. Unlike native species, tropical milkweed can remain green and flower all year, disrupting the monarch’s natural life cycle by encouraging them to breed late into the season when they should be migrating. Even more concerning, a year-round milkweed such as this can constantly harbor spores of Ophryocystis elektroscirrha (OE), a protozoan parasite that weakens monarchs, reduces their lifespan, and impairs their ability to fly.
In Santa Barbara County, native species like narrowleaf milkweed (A. fascicularis) and woollypod milkweed (A. eriocarpa) are best suited to support healthy monarch populations. These perennials are adapted to our local climate and go dormant in the fall, helping to signal the end of the breeding season and prompting monarch migration. Gardeners can support this natural cycle by cutting back native milkweed stems to 2 to 4 inches (5 to 10 centimeters) above the ground in October. This practice not only simulates natural senescence but also helps eliminate any OE spores that may be lingering on the foliage, reducing the risk of parasite transmission the following year. It’s also important to avoid overwatering or fertilizing milkweed late in the growing season, as this can prevent it from going dormant. Letting the plant follow its natural rhythm is essential for maintaining the delicate timing of monarch migration.
Beyond choosing the right species and supporting it properly, when planting milkweed, a good strategy is to establish it in small, connected patches rather than scattering individual plants. Monarchs are more likely to find and use clusters, so planting at least 10 to 20 milkweed plants together in a patch increases visibility and availability. Ideally, each patch should cover approximately 10 to 15 square feet (.9 to 1.3 square meters), with multiple patches spaced throughout a garden, park, or open space to create a “stepping-stone network” for monarchs. Grouping plants also helps support healthier growth by maintaining soil moisture and providing shade to young seedlings, while ensuring there are enough stems to sustain monarch caterpillars once eggs are laid.
Supporting Adults With Nectar Plants
While milkweed is essential for larvae, adult monarchs need diverse nectar sources to fuel their journey and reproduction. In Santa Barbara County, native plants blooming late into the summer can provide critical nourishment. Here are great options:
• California aster (Symphyotrichum chilense)
• Seaside daisy (Erigeron glaucus)
• Goldenrod (Solidago californica ssp. californica)
• California buckwheat (Eriogonum fasciculatum)
• Liveforever (Dudleya spp.) for dry slopes
Incorporating these species into your garden not only supports monarchs but also benefits a wide array of native pollinators, from bumblebees to hummingbirds. Even small gardens and patios can serve as refuges in supporting monarchs.
A Community Effort
Saving the western monarch is not a single-solution story; it is a network of connected actions across gardens, wildlands, and communities. At home, planting and caring for native milkweed and a variety of nectar plants creates vital breeding and feeding habitat. Observing monarchs and recording sightings of caterpillars, chrysalises, and adults on community science platforms like iNaturalist or Journey North helps researchers track population health and migration patterns. Community members can also join efforts such as the Western Monarch Thanksgiving Count each November, when volunteers survey overwintering sites up and down the California coast. Collectively, these actions — gardening with purpose, sharing observations, and contributing to long-term monitoring — form the backbone of monarch conservation in our region.
CITATION
Chrone, E. E., & Schultz, C. B. (2021, June 10). Resilience or Catastrophe? A possible state change for monarch butterflies in western North America. Ecology Letters, 24(8), 1533-1538. https://doi.org/10.1111/ele.13816
