Thank you for reaching out with your questions regarding milkweed in your area.
Your area of Oregon is not part of the natural range where milkweeds grow. They occur more inland/east. We do not recommend planting milkweeds outside of their native range as a conservation strategy for monarchs because it is unlikely to be visited by the butterflies. Monarchs only pass through your area of the Pacific Northwest in small numbers or in some years–if at all. The best thing you can do is plant native nectar plants that support the monarchs and other pollinators, as well as host plants for other butterflies more commonly found in your area.
For example, here are some other butterflies (with their host plants in parentheses) found in the Pacific Northwest that you can help support in your area:
- Western tiger swallowtail (willow, cottonwood, other trees)
- Silvery blue (lupines)
- Woodland skipper (grasses)
- Green comma (willow, birch)
- Ochre ringlet (grasses, rushes)
- Painted lady (thistles, mallow, legumes)
Here is a list of suggested nectar plants for monarchs in the maritime Pacific Northwest. This list contains plants which have documented monarch visitation, bloom during the times of the year when monarchs are present, are commercially available as seeds or transplants, and are known to be hardy. These species are well-suited for small wildflower gardens, have a diversity of bloom time, and the list includes water requirements for each of the plants so you can match plants to your soil conditions (or find plants for growing in containers). And here is a list of other good pollinator plants, for more than just monarchs.
For more inland areas of the Pacific Northwest, east of the Cascades, you can use our Milkweed Seed Finder tool to search for vendors in your area who supply seeds/plants of native milkweed species and here is a list of suggested nectar plants for the inland Northwest.
We do not recommend the planting of tropical milkweed (Asclepias curassavica) ANYWHERE in the U.S. as it is not native and research has shown that tropical milkweed encourages monarchs to lay eggs outside of their regular breeding season, disrupts their migratory cycle, and increases the prevalence of monarch infection by the protozoan parasite Ophryocystis elektroscirrha, commonly referred to as “OE” at levels that may harm the population (Batalden & Oberhauser 2015; Satterfield et al. 2015; Majewska et al. 2019; Majewska and Altizer 2019).
These negative impacts of tropical milkweed on monarchs stem from the fact that this milkweed species’ keeps its foliage year-round when it grows in areas where winters are mild and adequate moisture is available (particularly in the Gulf States and coastal & southern California). In contrast, the majority of native U.S. milkweeds are summer or fall-deciduous and do not have leaves during late fall and winter. If you already have tropical milkweed, we recommend removing it and replacing it with native milkweed (if appropriate) and nectar plants.
Want to find other ways to help western monarchs? Check out Xerces’ Western Monarch Call to Action and This Is How You Can Help resources to learn more. You can also explore and contribute observations of milkweeds and monarchs (when the butterflies are not overwintering) through the community science project the Western Monarch Milkweed Mapper: www.monarchmilkweedmapper.org. You can also explore our other community science project, the Western Monarch Thanksgiving Count here: www.westernmonarchcount.org which keeps track of monarchs during their overwintering phase.
For overall information and guidelines for western monarch conservation, check out Xerces’ Western Monarch Conservation page.
Please feel free to reach out if you have any additional questions.
Thank you for your efforts to support pollinator conservation in your community!
Stephanie Frischie, Ph.D.
Agronomist / Native Plant Materials Specialist, The Xerces Society
219 208 5879 (mobile)