The Monarch Butterfly Part II. Conservation Gardens in the Northern Plains
(E2236, May 2024)This publication helps home gardeners create attractive and functional garden habitat for monarch caterpillars and adults.
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Monarchs In Decline
The decline of monarch butterfly (Danaus plexippus) populations is a multifaceted problem driven by environmental challenges. The pervasive use of pesticides, persistent climate change, and abnormal or extreme weather events disrupt critical stages of their life cycle, including their arduous annual migration that spans up to 3,000 miles. However, amid this complex array of threats, one stands out as the primary catalyst for monarch decline: habitat destruction. The elimination of native milkweeds from agricultural, residential and urban landscapes, coupled with the illicit logging of trees in their overwintering sites in Mexico, poses an existential threat to monarch butterflies.
The steep reduction in milkweed populations emerges as a particularly alarming concern. As the sole host plant for monarch larvae, milkweeds are indispensable to the species’ survival. From 1999 to 2016, an estimated 850 million milkweed plants vanished from agricultural fields due to herbicide use, while the ongoing conversion of native prairie into cropland and urban sprawl continues to claim approximately 2 million milkweed plants annually. This decline deprives monarchs of essential breeding grounds and disrupts the delicate balance of their intricate ecosystem. As these vital plants rapidly disappear, the foundation of monarch survival hangs in the balance, underscoring the urgent need for decisive action to conserve their habitats.
This publication equips home gardeners with the knowledge necessary to create attractive and functional gardens that will serve as neighborhood oases for this important species. For more information on the monarch, see the companion publication, The Monarch Butterfly: Part I, Migration and Life Cycle at www.ndsu.edu/agriculture/extension/publications/monarch-butterfly-part-1-migration-and-life-cycle.
Planting Design
When designing the garden space, plant milkweeds in a border surrounding a patch of nectar-producing flowers and tall grasses. This configuration provides visual cues for flying monarchs seeking habitat in which to lay eggs. They are more likely to see milkweed plants on the perimeter of the garden than if they are in the middle of the planting. In a recent study, eggs and larvae were 2.5 to 4 times more abundant in conservation plots with this configuration than those with mixed or random patterns. Larvae developing on the milkweed will eventually form a chrysalis. When the adult butterfly emerges, it can easily find the nectar sources within the border. Consider the diagram below (Figure 1) to determine what strategies you can employ in your garden. If space in the garden is limited, an adjacent row of milkweed may serve in place of a border.
Flower Color of Nectar Plants
Research has shown that butterflies generally prefer white and warm colors such as yellow, orange, red, and pink, but monarch color preferences are more flexible. Monarchs make connections between the color of a blossom and the amount of nectar it provides. Such connections may aid adult monarchs in developing color preferences for nectar sources.
Monarchs respond to visual cues, and plants grouped by color act as highly visible beacons for migrating adults, more so than mixed plots. In the monarch conservation garden, it is more effective to organize plants in color blocks using multiple plants of the same species or cultivar together to increase their visibility from the air.
Plant Selection
Milkweed for Egg Laying and Larval Food
Milkweed is essential for monarch conservation; the species cannot exist without it. Therefore, milkweed should make up a majority of the plants in a monarch conservation garden. To attract monarchs to the garden, adult females must be able to detect those species that are best suited for oviposition. Egg-laying females make choices based on the height of the milkweed, preferring taller, more visually prominent plants near nectar sources. Adult females prefer laying eggs on swamp milkweed (Asclepias incarnata), which can range from 3- to 5-feet tall, over other species. Larvae in the same study developing on swamp milkweed experienced the highest survival rate and growth.
Swamp milkweed is an excellent choice for home gardens in eastern North Dakota because it thrives in moist loamy to clay soils and doesn’t spread via rhizomes like common milkweed (A. syriaca). Despite its name, swamp milkweed does not require wetland conditions and will thrive in a garden setting. However, the plants should be irrigated during times of drought to ensure survival.
Butterfly milkweed (A. tuberosa) is another well-behaved species that lacks rhizomes and does well in a compact gardening setting. This species is better adapted to the drier, sandier soils of central and western North Dakota and is short-lived on predominantly clay soils. The beautiful orange blossoms are produced earlier in summer than other milkweed species.
The nursery industry has released ornamental cultivars of the native species of both swamp and butterfly milkweed. Early studies show that the cultivars are similar to the wild species in attracting monarchs.
Common milkweed may be too aggressive for small gardens because it spreads vigorously by rhizomes and it also reseeds. This is an unwelcome plant in farm fields and is labeled as a noxious weed in a small number of counties in North Dakota. However, it is not labeled as a state noxious weed.
Like swamp milkweed, common milkweed is a preferred species for egg-laying adults and is necessary for the long-term survival of monarchs. Common milkweed is frequently planted in larger, naturalized areas such as pollinator meadows where the plant has room to spread. Showy (A. speciosa) and prairie (A. sullivantii) milkweed have beautiful flowers and are considered less aggressive than common milkweed. However, both species still spread by rhizomes and may be better suited for naturalized areas.
Studies show that monarchs are drawn to plots with multiple species of milkweed so consider adding more than one of the species listed in Table 1. Milkweed looks its best from June through September in North Dakota, but monarchs are still migrating south through October. Therefore, consider leaving milkweed undisturbed in the garden long into fall, even after it passes its most attractive stage.
Table 1: Milkweed selections for the monarch conservation garden
| Common Name | Scientific Name | Bloom Time | Flower Color | Moisture Conditions | Height (feet) | Risk of Spread |
|---|---|---|---|---|---|---|
| Butterfly Milkweed | Asclepias tuberosa | June-July | Orange- yellow | Dry to Mesic | 1-3' | Low; does not spread by rhizomes |
| Swamp Milkweed | Asclepias incarnata | July- August | Pink | Mesic to Wet | 3-5' | Low; does not spread by rhizomes |
| Showy Milkweed | Asclepias speciosa | June- August | Pink | Dry to Mesic | 1.5-4' | Medium; has rhizomes but somewhat less aggressive than common milkweed |
| Prairie Milkweed | Asclepias sullivantii | June- August | Pink | Mesic to Wet | 3' | Medium; has rhizomes but somewhat less aggressive than common milkweed |
| Common Milkweed | Asclepias syriaca | June- August | White, purple | Dry to Wet | 3-5' | High; will spread aggressively by rhizomes |
| Whorled Milkweed | Asclepias verticillata | May- September | White, green | Dry to Mesic | 1' | High; will spread aggressively by rhizomes |
Nectar Plants for Adults
Adult monarchs are sustained by nectar from many flowering plants and do best with a diverse collection. Non-native plants can provide nectar to monarchs just as adequately as natives, and native plant sources often are limited to what is popular at local nurseries. However, native plants sustain not only monarch butterflies but also native bee populations that have coevolved for the most efficient symbiotic relationship. Native plants are generally better adapted to local soil and climate conditions.
When choosing plants for a monarch habitat, select an array of plants that will bloom and provide nutrients to keep monarchs fueled throughout their migration (May-October). Avoid cultivars with double blooms (such as the Echinacea series Double ScoopTM), as these variants lack adequate pollen and nectar sources. Additionally, maximize plant diversity to increase natural pest management and total health of the garden ecology. Consider any of the plants listed in Table 2 as reliable options for North Dakota.
Other Elements
- Migration is thirsty work so consider adding a water source to conservation gardens. This can be a small pond, fountain or birdbath, or as simple as a small dish with still water and stones or marbles to prevent drowning.
- Trees and shrubs are great additions to the landscape adjacent to conservation gardens as they are useful to adult monarchs as overnight shelter and protection from harsh weather and predators.
- Avoid using insecticides in the monarch garden.
- Once you’ve implemented these criteria, get your pollinator garden certified by NDSU Extension as an official Pollinator Garden. Apply for certification at https://tinyurl.com/3mmyxtjn
Table 2: Floral resources for monarch butterflies in North Dakota
| Common Name | Scientific Name | Bloom Time | Flower Color | Moisture Conditions | Height (feet) | Comments |
|---|---|---|---|---|---|---|
| Butterfly Milkweed | Asclepias tuberosa | June-July | Orange- yellow | Dry to Mesic | 1-3' | Milkweeds also produce nectar and will attract other butterflies and bees |
| Black-eyed Susan | Rudbeckia hirta | June-September | Yellow | Mesic | 2-3' | Heat and drought tolerant |
| Purple Coneflower | Echinacea Echinacea angustifolia/ Echinacea purpurea | July | Purple-pink | Dry to Mesic | 3-4' | E. angustifolia is native to North Dakota |
| Swamp Milkweed | Asclepias incarnata | July- August | Pink | Mesic to Wet | 3-5' | Milkweeds also produce nectar |
| Spotted Joe Pye Weed | Eutrochium maculatum | July- August | Pink | Mesic to Wet | 6' | Smaller ornamental cultivars can be found in garden centers |
| Wild Bergamot | Monarda fistulosa | July- August | Pink-purple | Dry | 2-5' | Monarda didyma cultivars are smaller and can be found in garden centers; the native wild bergamot may be too large and sprawling for a small garden |
| Prairie Blazingstar | Liastris pycnostachya | July- August | Pink-purple | Mesic to Wet | 2-4' | Does best in medium to wet soils |
| Meadow Blazingstar | Liatris lingulistylis | August | Pink-purple | Mesic to Wet | 3-5' | Pollinator magnet |
| Smooth Blue Aster | Symphyotrichum laeve | August-September | Blue-purple | Mesic | 6’ | Lovely blue flowers |
| New England Aster | Symphyotrichum novae-angliae | August- September | Pink-purple | Dry to Wet | 6' | Fuel for migrating monarchs; smaller ornamental cultivars may be found in garden centers |
| Showy Goldenrod | Solidago speciosa | September-November | Yellow | Mesic to Dry | 4-5' | Non-rhizomatous |
Pest Control in the Monarch Garden
In a thriving garden, diverse insect populations facilitate essential ecological processes such as pollination, natural pest control, nutrient cycling, and provide a primary food source for various other garden inhabitants including birds, small mammals and reptiles. Increased insect activity in such a garden not only signifies its vitality but also highlights the intricate web of life that sustains it, promoting resilience, productivity and sustainability. Therefore, when you cultivate a garden enriched with plant diversity, expect to host a flourishing community of insects.
Some insect pest populations may spike under rare conditions such as a lack of predator populations, an excess of foraging sources or an outbreak of plant disease. While the easiest and most natural approach is often to allow pests to be managed by nature itself, there are effective methods for controlling garden pests without jeopardizing the welfare of critical pollinator species. The oleander aphid (Aphis nerii), for instance, is a common milkweed pest that can be dislodged from affected plants by a strong jet of water. Use this method with discretion, as monarch eggs can be evicted from leaves as well.
