Milkweed and Monarchs

Monarch Caterpillar on Milkweed

A Monarch caterpillar on its host plant, milkweed.
Image by Sara Codair

Milkweed (Asclepias) is perhaps best known as being the only plant that the endangered Monarch butterfly uses to lay its eggs and the only plant that Monarch caterpillars (larva) can eat. As the name implies, milkweed exudes a toxic white latex when the plant cells are damaged. Despite being toxic to many other insects and mammals, Monarch caterpillars have evolved to feed exclusively on the poisonous leaves, which has the added benefit of rendering them distasteful to predators!

Although milkweed is critical to the survival of the Monarch butterfly and its other close butterfly relatives (Danaus spp.), these plants also support other pollinators. Often the flower umbels are abuzz with wasps, bees and other insects feeding on the nectar. You can find two native milkweed species in the gardens here at Heaps Peak Arboretum (HPA). 

Studies suggest that mixing your plantings of milkweed with other native wildflowers can help Monarchs lay up to 20% more eggs on your plot. It’s great news for the many gardeners who don’t find milkweed particularly beautiful by itself, but view it as quite attractive mixed among other blooming plants. It might not come as a surprise that mimicking nature with a diverse variety of native plantings in your garden provides the greatest benefit to many species. Butterflies require lots of nectar for flight and reproduction, so having the support of other native wildflowers would seem to make a lot of sense.

Unfortunately, increases in herbicide use, habitat loss and other environmental changes have caused milkweed populations to dramatically decline. The loss of milkweed is a major reason that a dramatic 97% of California’s monarch butterflies have disappeared since the 1980s. At HPA we don’t use herbicides or other pesticides and hope to inspire our local community to reduce their use as well. Nationally, efforts are underway to protect milkweed habitats, which are vital to the survival of Monarch butterflies. You can help by acting locally in your own garden no matter the size.

Help Monarchs and other pollinators by…

  • Using fewer pesticides and herbicides in your gardens.
  • Propagating your own plants from seeds or cuttings to avoid pesticide use.  
  • Asking for plants and seeds that are USDA certified organic, and shop at nurseries that use “Pollinator-Friendly Pest Management” when buying retail.
  • Being marketing savvy. At retail shops, plants that attract pollinators may be labeled as “pollinator friendly,” but that doesn’t necessarily mean they are free of pesticides harmful to pollinators. Terms like these are not regulated or formally defined. 
  • Using organic gardening options when deciding to use any pesticides or herbicides.
  • Planting native milkweed species!
  • Planting other native nectar plants like local wildflowers.

Gardening FAQs

When should I plant milkweed?
In our local area, we find that fall is best. Some species depend on the change in temperature for germination, and the cooler weather helps the plants establish. Milkweed may also be planted in the spring.

Where can I get milkweed?
We usually sell milkweed plants at our spring and fall native plant sales. Some nurseries offer our local varieties, such as Tree of Life and Theodore Payne.

Which species of milkweed should I plant?
Varieties you find at garden centers may not be native to your area and ideal for Monarchs. You can find what milkweed species is local to your area with this milkweed range map

How should I handle milkweed?
When handling milkweed and other plants with irritating milky sap, use gloves and avoid contact with eyes and skin.

Should I grow milkweed from seed?
It’s often difficult to sow the seeds on the ground. We usually recommend using plants, especially because pollinators need them now.

What should I plant with milkweed?
Many wildflowers are great companion plants for milkweed! Butterflies tend to visit flowers that are easy to land on including yarrow, wallflower, phacelia, buckwheat and golden yarrow. 

Is milkweed safe for my pets?
Pets typically do not eat milkweed, but it can be toxic when ingested in large quantities. This is usually only an issue for grazing animals when other food is scarce. 

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