Habitat loss is one of the most significant contributors to declining Monarch butterfly populations. There are fewer milkweed stands than ever before due to increased land development for agricultural and other uses and increased efficiency of herbicides used to control non-crop plants.
Monarch butterflies depend on milkweeds as host plants, meaning they will only lay eggs on these plants because milkweed is all Monarch caterpillars eat. This specialized diet offers some protection from predators. Milkweeds contain poisons knowns as cardiac glycosides, which Monarchs have evolved to assimilate. These toxic compounds make them distasteful to many predators.
There are 13 species of milkweed native to Ohio that Monarchs will use as host plants:
- Butterfly weed
- Clasping-leaved Milkweed
- Common Milkweed
- Green Milkweed
- Green-flowered Milkweed
- Honey-vine
- Poke Milkweed
- Purple Milkweed
- Spider Milkweed
- Sullivant’s Milkweed
- Swamp Milkweed
- White Milkweed
- Whorled Milkweed
Butterfly weed, common milkweed, purple milkweed, Sullivant’s milkweed and swamp milkweed are preferred larval hosts. Of these, butterfly weed, common milkweed and swamp milkweed are the most readily available in seed packets and as live plants from a local nursery. You can narrow down what will work in your yard or garden based on the growing conditions that are present.
Butterfly weed
Height. Butterfly weed is the shortest variety of the three, growing to about 2-3 feet tall in a garden.
Conditions. Butterfly weed grows best in a dry, sunny location with alkaline soil.
Flowers. It takes a couple of growing seasons before butterfly weed will bloom when planted from seed. Once it reaches maturity, it will attract a number of pollinators and butterflies with its bright orange blooms throughout the summer. The bloom period can be extended by cutting butterfly weed flowers back to keep them from going to seed.
Planting. Milkweed seeds are best sown in the fall at a depth no deeper than ¼ inch. They can also be started indoors and transplanted during late spring, but the seeds must be stratified in the refrigerator for several weeks before planting to spur germination. If you buy live plants from a nursery, choose smaller ones as they will establish more easily.
Swamp milkweed
Height. Swamp milkweed grows to about 3-4 feet tall. Each plant usually has a single stem with branching near the top.
Conditions. This variety prefers to grow in damp to wet soil near ponds or bogs in full sun or partial shade. However, it can be grown in drier locations with supplemental watering. It grows naturally in abandoned fields and areas with disturbed soil. It does not like being crowded by other plants, can become unsightly in the fall and is a magnet for aphids. It works best when planted as a border rather than in a garden.
Flowers. Swamp milkweed gets flat pink to purple flower clusters at the top of its stems in July and August. Its flowers give off a faint cinnamon order.
Planting. Seeds are best sown in the fall at a depth of ¼ inch. They can also be planted in the spring after several weeks in the refrigerator. If you purchase swamp milkweed as a live plant, make sure it is in the ground before the end of spring and stick to smaller ones for easier establishment.
Common milkweed
Height. Common milkweed is the tallest of the three varieties, typically, growing to about 3 feet tall and, occasionally, reaching heights of up to 5 feet. Like swamp milkweed, it grows as a stalk with some branching at the top.
Conditions. Common milkweed grows best in sunny, dry locations but can survive in a variety of conditions. It’s probably better suited to a wildflower garden than a well-manicured garden because it spreads by rhizomes and can form large clumps.
Flowers. Common milkweed flowers grow in ball-shaped clusters that range in color from pink to light purple. The blooms give off a sweet scent that can be detected many feet away. This variety also gets large, comma-shaped seed pods that are thick and covered with spines.
Planting. Sow seeds during the fall at a depth of ¼ inch or in the spring after stratifying your seeds in the refrigerator. If you purchase and plant live plants, transplant them outdoors before the end of spring. Smaller live plants will transplant easier.
Tips
- Milkweed plants grow easily when planted from seed, so starting them that way in the fall is your best bet.
- Make sure the location you choose provides enough room for the varieties you chose to thrive and accommodates their growing needs. Milkweed plants have large taproots and do not transplant well.
- Have patience getting your milkweed stand established. Most varieties grown from seed will not flower until their second year.
- Milkweeds are important host plants and do provide some nectar to adult butterflies and other pollinators, however, you should consider adding some native wildflowers to the mix, too. Some preferred varieties include:
- Ashy Sunflower
- Black-eyed Susan
- Dense Blazing-Star
- New England Aster
- Ohio Goldenrod
- Ox-eye Sunflower
- Prairie-dock
- Purple Coneflower
- Rattlesnake-Master
- Shale-Barren Aster
- Smooth Aster
- Spotted Joe-Pye
- Stiff Goldenrod
- Tall Ironweed
- Narrow Leaved Mountain Mint
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