Swamp Milkweed

Here's a guide to planting Asclepias incarnata (Swamp Milkweed) seeds in the USA, covering both direct sowing and starting indoors:

Site Selection
Sunlight: Swamp milkweed thrives in full sun, needing at least 6-8 hours of direct sunlight daily.  
Soil: It prefers moist to wet, well-drained soils. It can tolerate some clay or sandy soils, but good drainage is essential.  
Location: Choose a spot that allows for their mature size (3-5 feet tall, 2-3 feet wide). They make a great addition to the back of borders, naturalized areas, or near ponds or streams.  

Direct Sowing Outdoors
Fall Planting: Sow seeds in the fall before the first frost. This allows for natural stratification over winter.
Spring Planting: Sow seeds in early spring as soon as the soil can be worked.
Soil Preparation:
Clear the area of weeds and debris.
Amend the soil with compost or other organic matter to improve drainage and fertility.  
Rake the soil to a fine tilth.
Planting Depth: Sow seeds no more than ¼ inch deep. They need light to germinate.
Spacing: Space seeds about 1-2 feet apart.
Watering: Keep the soil consistently moist until seeds germinate and seedlings are established.

Starting Seeds Indoors
Timing: Start seeds indoors 8-10 weeks before the last expected frost in your area.
Containers: Use seed starting trays or pots with drainage holes.
Soil: Use a sterile seed starting mix.
Planting Depth: Sow seeds ¼ inch deep.
Watering: Keep the soil consistently moist but not soggy.
Light: Provide ample light, either with grow lights or a sunny window.
Transplanting: Harden off seedlings by gradually exposing them to outdoor conditions for a week before transplanting. Transplant after the last frost, spacing plants 1-2 feet apart.

Stratification
Swamp milkweed seeds need cold stratification to germinate well. If sowing seeds in the spring, you can mimic this process by placing seeds in a sealed bag with moist sand or vermiculite in the refrigerator for 4-6 weeks before planting.  
Scarification
Scarification (scratching or nicking the seed coat) is not necessary for swamp milkweed.

Maintenance Tips
Watering: Water regularly, especially during dry periods. Swamp milkweed prefers consistently moist soil.  
Fertilizing: They generally don't need fertilizer, but a balanced fertilizer can be applied in early spring.
Staking: Taller plants may need staking to prevent them from flopping over, especially in windy areas.
Deadheading: Remove spent flowers to prevent self-seeding if desired.
Pest and Diseases: Watch for common milkweed pests like aphids and milkweed bugs. Diseases like powdery mildew can occur in humid conditions.

Invasiveness
Swamp milkweed is native to the eastern US and is not considered invasive in most areas. However, it can spread by rhizomes (underground stems) and self-seeding, so monitor its growth and remove unwanted seedlings if necessary.  

Additional Notes
Swamp milkweed is a crucial host plant for monarch butterflies.  
It blooms in summer, providing nectar for pollinators.

Native Plant Map

Dark Green indicates the plant is native within the state, yellow rare,
the lime green indicates where the plant is native and seen more within a
state.

Map Credits BONAP©2024