CREATING A CALSCAPE PLANT LIST FOR MONARCH HABITAT By Carrie Strohl

This article originally appeared in the Summer 2026 Napa Valley Chapter CNPS newsletter.

In 2015, I had 17 monarch butterfly caterpillars in my Napa backyard in part because I had planted a single narrow leaf milkweed plant that had spread across the yard. I’ve heard people say, “I planted milkweed but no monarchs have come” and while milkweed is the obligate host of this symbolic butterfly, milkweed alone is not sufficient. A habitat also needs enough nectar resources to support the adult butterflies that emerge from their chrysalides. Solano Resource Conservation District recommends starting with at least 10 native milkweed plants and a 2:1 nectar:milkweed ratio. More recently I embarked on the task of making a plant list for planting monarch habitats in school gardens.

First, I consulted three reports from leading conservation organizations: the Environmental Defense Fund, Solano County Resource Conservation District and Xerces Society. Then I turned to the CNPS online resource Calscape. I created a list and added monarch-specific recommended plants from the reports I read. Calscape has a feature that allows you to export data from the list to an Excel spreadsheet with the option to include key characteristics such as the total number of butterflies and moths supported. To narrow down the list, I sorted the list by that number: most = Ribes aureum (84) to least = Baccharis pilularis ‘Pigeon Point (0). It’s important to note that these are numbers of supported organisms documented. Zero may just mean the plant hasn’t been studied closely enough. For example, the Calscape entry for Baccharis pilularis ‘Pigeon Point’ indicates that it supports bats, caterpillars, and moths.

The final selection was also based on several other factors. The ultimate goal was to create a list with a realistic number of plants (36) that were: affordable (<$500 total), easily accessible (or easy enough to make accessible through propagation efforts), the right size for a 200 sq. ft. installation, and offered a range of bloom times. Plants had to be suitable for school garden settings (size, safety, maintenance, etc.); varieties were omitted if too big (common Manzanita can get up to 10 x 20ft.!), too difficult to get (Arcto. stanfordiana, carried by only 4 nurseries), or too sharp (e.g., Cobweb Thistle).

To date, this plant list has worked at four school sites in Napa County. At each site, 5-6 different nectar plants (in multiples) were planted, plus at least 1 milkweed plant for every 2 nectar plants. Many of these plants were propagated by our own local team or procured at our fall plant sale. View the Monarch Habitat Plant List or create your own Calscape list, visit calscape.org.