Gardening with Native Plants: Supporting Monarch Populations

Monarch on sweet black-eyed Susan (Photo: Susan Carpenter)

Monarch on sweet black-eyed Susan (Photo: Susan Carpenter)

This month’s long days bring the transition from spring into summer. Our native plant garden activities include planting, weeding, edging, mulching, and mowing. We are also monitoring bumble bees and other pollinators in the garden.

Woodland spring ephemerals have set seed and many species have died back for the year. Later spring flowers wild geranium (Geranium maculatum) and Virginia waterleaf (Hydrophyllum virginianum) finish blooming, leaving a leafy green understory beneath the tree canopy. Early prairie blooms like prairie smoke (Geum triflorum), shooting star (Dodecatheon meadia), and wood betony (Pedicularis canadensis) also set seed in June, and late spring species like spiderwort (Tradescantia ohioensis), wild white indigo (Baptisia alba), and downy wood mint (Blephilia ciliata) continue to flower.

We usually see the first monarch butterflies of the season at the Arboretum in late May. These adult butterflies are not the ones that migrated south last September. Rather, they are the offspring of those butterflies who migrated north this spring (from the overwintering area in Mexico) to the southern U.S. and reproduced. In Wisconsin, there are 2 or 3 successive summer generations, which ideally build population numbers to counter losses from the population during migration, overwintering, or losses due to other stressors.

The spring migrating adults and following summer generations require healthy and abundant milkweed on which to lay eggs. Milkweed plants are the only food source for larvae. The population also depends on healthy and abundant nectar sources—flowers—which provide nutrition for the adult butterflies from May through September.  Does your garden have both of those food sources?

Monarch adults nectar on milkweed, but they are not significant pollinators for it. Milkweed has a very specialized system for pollen transfer, and large bees must visit the flowers to successfully pollinate flowers to initiate pod and seed production. From the many clustered flowers on each milkweed plant, only a small number of pods will develop. Each pod contains hundreds of wind-dispersed seeds, which need to reach suitable habitat to produce new plants.

How can your gardening practices support monarchs? Grow native milkweeds, matching the habitat needs of each species with your garden conditions. Encourage and monitor milkweed reproduction in your garden. Plant and nurture a wide diversity of native wildflowers blooming throughout the season in prairie and savanna gardens. These nectar sources will support monarch adults and bee pollinators that are an essential part of the system.

Besides providing abundant milkweed and nectar sources, you can support monarchs by eliminating the use of pesticides, especially systemic insecticides (e.g., neonicotinoids). Check nursery plants you purchase to make sure they were not pre-treated with insecticides when they were being grown.

Include trees and shrubs in the landscape, as these taller spots are often where the chrysalis stage is found, and where the adult butterfly emerges and expands its wings.

Learn more about monarchs and monitoring projects at Monarch Joint Venture and at the lecture Conserving Monarch Butterflies: All Hands on Deck, on Thursday, June 22, at 7p.m., in the Arboretum Visitor Center. The speakers are monarch researchers Laura Lukens and Kyle Kasten of the University of Minnesota. This event is free, but registration is required. Please join us!

—Susan Carpenter, Arboretum native plant gardener