Monarchs pass through Missouri twice a year and raise families here in between. A garden can help with both: milkweed for the caterpillars, and flowers for the adults, especially in fall.
The monarch year in Missouri
- Spring: Monarchs fly north from their wintering grounds in Mexico and reproduce in Oklahoma and Texas. Their offspring continue north into Missouri.
- Summer and fall: Monarchs produce broods in Missouri in summer and fall (Missouri Department of Conservation).
- Fall migration: Monarchs head to Mexico in late summer and fall. Peak numbers pass through Missouri in mid-September.
MDC describes the monarch as declining throughout North America, and adds that everyone can do something to help. Planting milkweed is one of the most direct ways.
Why milkweed
Monarch caterpillars feed only on milkweed leaves (USDA Forest Service). Adult monarchs drink nectar from many flowers, but they breed only where milkweeds are found. The caterpillars store the milkweed’s bitter cardiac glycosides in their bodies, which makes them distasteful to predators.
The Missouri Department of Conservation counts 22 species of milkweeds in Missouri. Our series includes three that grow from seed and suit three different kinds of ground.
Which milkweed goes where
| Butterfly Milkweed (No. 4) | Swamp Milkweed (No. 5) | Common Milkweed (No. 6) | |
|---|---|---|---|
| Botanical name | Asclepias tuberosa | Asclepias incarnata | Asclepias syriaca |
| Flowers | Bright orange, June–August | Rose-pink, vanilla-scented, June–September | Dusty pink, fragrant, May–August |
| Height | 1½–2 ft | 3–5 ft | 3–5 ft |
| Light | Full sun | Full sun to light shade | Full sun |
| Soil | Dry to average, well-drained | Average to wet; thrives in clay | Dry to average; adaptable |
| Habit | Deep taproot; not weedy | Upright; seeds float off on the wind | Spreads by roots into colonies |
| Best for | Hot, dry beds and slopes | Rain gardens, low spots, clay | Meadows and big open spaces |
Plant all three if you have the room, or start with the one that fits your yard. The Monarch Milkweed Trio has all three in one sleeve.
Growing milkweed from seed
All three need about 30 days of cold, moist conditions before they’ll sprout (Prairie Moon code C(30)).
- Sow between November and February outdoors, on bare ground or in winter-sowing jugs, about 1/8 to 1/4 inch deep. See our winter sowing guide.
- Or chill the seed in the fridge for 30 days in damp sand and sow after the last frost. See the fridge method.
- Sow Butterfly Milkweed where it will stay. Its long taproot makes moving it risky once it’s established.
- Mark the spot. Butterfly Milkweed is slow to emerge each spring.
- Be patient. Prairie Moon says Butterfly Milkweed can take one to three years to bloom from seed. Common Milkweed is one of the easiest and fastest milkweeds to establish.
Feed the adults too
Caterpillars need milkweed; adults need nectar from spring through fall. Migrating monarchs especially need plenty of nectar to build fat reserves for the trip south (USDA Forest Service). In September, look for them on New England Aster (No. 10), which MDC names as a fall monarch flower. Rough Blazing Star (No. 9) feeds them in late summer.
Let the caterpillars eat
Chewed, even bare, milkweed leaves are the point. Grow Native! notes that Butterfly Milkweed’s foliage may be stripped bare by caterpillar feeding. That’s the plant doing its job. A few more tips:
- Skip insecticides on and around milkweed. Caterpillars are insects too.
- Aphids are common on milkweed. The Lady Bird Johnson Wildflower Center suggests leaving them for ladybugs, or rinsing them off with a strong spray of water or soapy water if the plant looks stressed.
Milkweed safety
- Toxic if eaten. The ASPCA lists milkweeds as toxic to dogs, cats and horses.
- Sap can irritate. NC State Extension notes the sap can cause skin and eye irritation. Wear gloves if you’re sensitive, and wash your hands after handling.
- Livestock. USDA researchers report milkweed poisoning in sheep and cattle and occasionally horses, usually when other forage is scarce or milkweed ends up in hay. Don’t plant it in pastures or hay fields.
What about tropical milkweed?
We don’t recommend it. The Xerces Society advises against planting tropical milkweed (Asclepias curassavica) in the US: where it stays green through winter, a monarch parasite called OE can build up on it, and it may cause monarchs to breed instead of migrating. Xerces suggests native milkweeds, such as butterfly weed, instead.
Sources: Missouri Department of Conservation Field Guide (Monarch; Milkweeds; Butterfly Weed; Swamp Milkweed; Common Milkweed) and Xplor (Sept. 2022); USDA Forest Service, “Monarch Butterfly Habitat Needs”; Grow Native!; Prairie Moon Nursery; Lady Bird Johnson Wildflower Center; NC State Extension Gardener Plant Toolbox; ASPCA Animal Poison Control; USDA Agricultural Research Service Poisonous Plant Research Lab; Xerces Society, “Tropical Milkweed—a No-Grow” (2018). Full links in our sources list.