URBANA, IL -- Most gardeners believe that monarch butterfly populations are declining due to the lack of milkweed in the summer breeding areas of our state. However, researchers Greg Spyreas and David Zaya with the Illinois Natural History Survey are proving there may be more to the monarch story than milkweed.
Illinois is home to 19 native milkweeds. In the last 20 years, milkweed has decreased by 95 percent in agricultural fields, Zaya says. “However, natural areas are buffering that loss, enabling the monarchs to build up their normal population numbers throughout the summer.”
Plant ecologists like Spyreas and Zaya now believe the decline in the monarch population may also be due to a lack of floral resources during the butterflies’ journey back to Mexico. To provide resources to monarchs on their long voyage, scientists are urging gardeners to create a monarch corridor, also known as a floral highway.
Creating floral highways requires planting fall-blooming perennials in gardens in addition to milkweed. “Keep planting milkweed, of course. It’s a larval food source for caterpillars and a highly sought-after nectar resource for adult monarchs,” Zaya says..
If you plan to add new plants to your garden or to begin building a new landscape, Spyreas has several plant recommendations. “Fall-blooming perennials like liatris, joe pye weed, blackeyed Susan, bee balm, aster, coneflower, and helianthus would be excellent additions to your gardens for the late feeding of monarch butterflies,” he says.
Liatris pycnostachya (prairie blazingstar) blooms in mid to late summer on large upright spikes in pink or purple. This plant requires full sun, and is not drought tolerant when young.
Eutrochium purpureum (joe pye weed) blooms in mid-summer to early fall with a pink or purplish-pink panicle of compound flowers. It requires light shade to partial sun.
Rudbeckia hirta (blackeyed Susan) blooms in early to mid-summer with a dark brown central cone and yellow petal-like rays. It requires full sun and is an easy-to-grow but short-lived biennial.
Monarda spp. (bee balm) blooms in summer for up to two months with a 3 to 4 inch ring of tubular flowers ranging from pink to red. This plant requires partial sun and moist conditions.
Symphyotrichum shortii (smooth blue aster) blooms in late summer to fall with flowers featuring blue-violet petal-like rays and a yellow center which last one to two months. It requires partial to full sun and regular pinching to keep compact.
Echinacea purpurea (purple coneflower) blooms mid to late summer with a central brown cone with purple or pink petal-like ray flowers. The plant requires full to partial sun and prefers well-drained soil and is drought tolerant once established.
Helianthus mollis (downy sunflower) blooms in late summer to early fall with a large bright yellow composite flower. It requires full sun, tolerates drought, and forms dense colonies.
Additional gardening practices like adding a water source, planting multiples of one plant type in groups, avoiding pesticide use, allowing herbs to flower, and planting annuals like Mexican sunflower, zinnias, and cosmos can be of great benefit to the traveling monarchs.
University of Illinois Extension horticulture educator Kelly Allsup says, “By creating a floral highway to help the monarchs, you will also help a host of other pollinators and wildlife by creating habitat they need to survive.”