Phoenix residents are being asked to make space for monarchs in a city where native plants can provide both food and shelter during migration. Mayor Kate Gallego joined that effort Monday by planting milkweed outside Phoenix City Hall; milkweed is the only plant monarch caterpillars can eat. Monarchs passing through Arizona are migrating south from Canada and the northern United States, with some traveling nearly 3,000 miles to their wintering grounds.
Phoenix lies along a monarch migration route, according to KJZZ, and the city is asking residents to plant milkweed and other habitat plants. Gallego signed the National Wildlife Federation's Mayors' Monarch Pledge in April 2021, and the city later proclaimed September Planting for Monarchs Month, according to 12News. The City Hall effort builds on an existing 300-square-foot monarch demonstration garden near the City Hall Council Chambers.
The city's larger plantings have been concentrated at mountain parks and along the riverfront, while Phoenix plans to expand monarch habitat downtown, according to KJZZ. Residents can also contribute by growing milkweed in their yards, giving monarch caterpillars the host plant they need to develop before migration.
Timing the Plantings for Peak Migration
Milkweed sowing should account for seasonal conditions. Regional observational data show monarch activity in the Phoenix area climbing late in the month and peaking around November 1, but MyWild says that sightings peak is influenced by resident monarchs and is not the best measure of migration timing; Monarch Watch places the migration midpoint near Arizona's latitude around October 7. MyWild recommends sowing milkweed seed around November 15, using autumn's cold, moist conditions to support germination.
The City of Phoenix also distributes free milkweed seed packets through its public libraries, and annual events like NatureFest PHX include monarch-tagging activities. Desert milkweed and Arizona milkweed are among the region's native milkweed species. Officials steer growers away from tropical milkweed varieties, which can disrupt monarchs' migration timing and spread parasites, the same report notes.
How Phoenix gardens fit together
The City Hall demonstration garden is part of a broader network of projects rather than the city's only monarch planting. According to the City of Phoenix, a separate pollinator garden was completed at the Phoenix Convention Center at Washington and 3rd Streets on Nov. 6, 2024, with another planned for the North Building. A Jan. 22, 2026, Phoenix Parks and Recreation Board packet also described a proposed monarch and pollinator garden at Barrios Unidos Park. The records distinguish these projects by location and planning history; they do not establish that their plantings, irrigation or maintenance are identical to those at City Hall. For residents establishing native milkweed and nectar plants in Phoenix's heat, the city's Water Services Department recommends watering between sundown and sunrise to reduce evaporation and adjusting watering to weather and plant needs, according to Phoenix Water Services.
A Steep Decline Behind the Urgency
The push comes as western monarch numbers hit alarming lows. The Xerces Society's annual Western Monarch Thanksgiving Count tallied only 12,260 overwintering butterflies across 249 California sites in January 2026, according to the National Wildlife Federation — a second straight year of critically low counts and part of a population decline exceeding 99% since the 1990s. Monarch Joint Venture reports that more than 4.5 million monarchs wintered in California in the 1980s and cites research suggesting that at least 30,000 may be needed to sustain the western migration, while cautioning that the precise threshold is unknown. Eastern monarchs, which winter in Mexico rather than California, aren't faring much better: that population occupied just 7.24 acres of overwintering forest during the 2025–2026 season, well below the 15-acre threshold scientists say is needed to avoid migratory collapse, according to the Center for Biological Diversity.
Federal protection for the species remains stalled. The U.S. Fish and Wildlife Service proposed listing the monarch butterfly as threatened under the Endangered Species Act in December 2024, but officials delayed a final ruling in late 2025 by classifying it as a long-term action, pushing any decision to late 2026 at the earliest, according to the Xerces Society. That regulatory limbo is part of why city-level efforts like Phoenix's have taken on outsized importance for conservationists.
Arizona's Unique Spot on the Migration Map
Arizona is part of the monarchs' migration route. Statewide, Arizona wildlife officials and conservation partners have also launched milkweed restoration projects at sites like the Whitewater Draw Wildlife Area, part of a 50-year Western Monarch Butterfly Conservation Plan targeting a 74% monarch decline across seven western states, according to Cronkite News.
Phoenix's Desert Botanical Garden backs the city's pledge through its Great Milkweed Grow Out program, offering scientific guidance and promoting native nectar plants such as Goodding verbena, flattop buckwheat and mistflower. Those plants supply energy for adult monarchs, while milkweed hosts their caterpillars, making a mix of host and nectar plants important to the city's habitat efforts.
