Monarch butterflies are in trouble: over the past few decades, scientists have seen substantial declines in populations of these iconic orange and black butterflies. But there are things we can do to help support monarch butterflies right now.  

Did you know that there are two main populations of monarch butterflies? The large population of monarchs found east of the Rocky Mountains is referred to as the Eastern Monarch population. This group makes the iconic and remarkable migration to Mexico each fall.

If you live in San Diego or anywhere west of the Rocky Mountains, the monarchs you see are part of the Western Monarch population. These butterflies do not migrate to Mexico, but overwinter along the California coast during the fall and winter months. During overwintering, monarchs roost in trees. They typically stop breeding until temperatures warm up in early spring and the native milkweeds begin to sprout, providing the habitat the monarch caterpillars need to survive.

Here are three simple ways you can help monarchs during fall and winter in order to welcome them into gardens this spring.

Prepare for spring: plant native.

Restoring native plant habitat is vital to preserving biodiversity. And now is the time to do so—seasonal rains during the cooler months of fall and winter will help the plants become established. It’s important to purchase plants from nurseries that do not use pesticides, especially systemic pesticides. These get into the plants’ tissues and contaminate nectar, pollen, and foliage, which has devastating effects on the insects that feed on those plants.

• Plant a variety of native flowering plants / nectar sources. Milkweed and flowering plants are needed for monarch habitat; adult monarchs feed on the nectar of many flowers, and they breed only where milkweed is found. Choose plants with varying bloom times so nectar is available to monarchs and other pollinators throughout the year. The California Native Plant Society – San Diego Chapter website has lots of information about where to buy native plants.

• Plant native milkweed seeds. Milkweed planted from seed appears to do best when the seed has been given some time in cold conditions. Seeds can be ‘cold stratified’ in a refrigerator, but if you plant during the cool months, this occurs naturally. If you already have native milkweed in your garden and it looks dead, don’t worry. It goes dormant over the winter, but will re-sprout in the spring. If you’ve planted milkweed seeds but they haven’t germinated, don’t give up—they will sprout when the weather warms up in the spring.

• Looking for native milkweed to add to your garden? Narrowleaf milkweed, the most commonly found native milkweed in San Diego County, as well as a few other native species are available at several local nurseries including:
• Butterfly Farms in Encinitas
• Nurseries that sell Moosa Creek plants
• Native West’s seasonal plant sales

Cut back tropical milkweed.

Tropical milkweed (which has red or yellow flowers) does not go dormant in the winter like native milkweeds do. As a result, it provides breeding habitat all year long. This may sound like a good thing, but it’s not. Scientists believe the presence of tropical milkweed can interfere with the monarch’s overwintering pattern and increase diseases like Ophryocystis elektroscirrha (OE), which causes deformed wings and shortens lifespans.

Growing native milkweed is always preferable, but if you have tropical milkweed in your garden, it’s best to cut it back in the fall to a few inches above ground. Keep cutting it back when new growth appears until early spring.

Monitor overwintering: get involved with community science.

The overwintering monarch population is assessed through an incredible community science effort called the Thanksgiving and New Year Count, where all known overwintering sites across the state are monitored by volunteers. This is how scientists measure the health of and fluctuations in the Western monarch population, and how they know it has declined by 99% since the 1980s. In 2022, these monitoring events run from November 12–December 4 and then December 24–January 8. Learn more. 

The San Diego Pollinator Alliance is a network of organizations and agencies working on monarch and pollinator health issues. Members include the Resource Conservation District of Greater San Diego County, Butterfly Farms, Sky Mountain Permaculture, the California Native Plant Society–San Diego Chapter, U.S. Fish & Wildlife Partners for Fish & Wildlife Program, the Natural Resources Conservation Service, and the San Diego Natural History Museum. The Alliance is in the process of developing a seed and plant source of locally collected native milkweed, which will be available for home gardens and restoration projects starting in spring 2021. Join the Pollinator Alliance’s mailing list to keep up to date.

Western Monarchs roost in trees as they overwinter along the California coast. Photo courtesy of U.S. Fish & Wildlife Service.

The Western Monarch population has decreased by 99%, with less than 30,000 butterflies remaining. Photo courtesy of U.S. Fish & Wildlife Service.

Posted by guest blogger Ann Baldridge, community programs director at the Resource Conservation District of Greater San Diego County and member of the San Diego Pollinator Alliance on November 30, 2020