Joe Pye weed (Eupatoriadelphus fistulosus) is a wildflower native to the eastern half of the United States in USDA horticultural zones 3 to 9. It grows to 6 feet tall and has a hollow stem with large oblong leaves up to 10 inches long. The plants can form dense colonies if grown in the right conditions--damp or wet rich soils. The flowers are attractive to a number of butterflies, and the plant can produce flowers during most of the growing season if conditions are suitable. Several improved varieties are available with brighter or darker blooms than the wild version.
Collect Joe Pye weed seeds by finding flower heads that are faded and dry and you can plainly see the tiny thin seeds still attached to the base of the flower heads. Each seed has a tiny bit of fluff attached to it so the wind can carry it away from the mother plant. Carefully cut the stem below where the seeds are attached to the old flower head with hand shears and place the old flower head in a paper bag. Seeds are usually available for harvest in late summer and early fall.
Shake the seed from the flower heads and store the seeds in the paper bag in a cool (60 to 75 degrees F) location. Store for as long as four weeks without refrigeration if you are planning on planting the seeds in the fall. If you are planting the seeds in the spring and holding them over the winter, store in an open paper bag in the refrigerator for at least six weeks. The cold temperatures increase the sprouting or germination rate.
Locate an area of the garden that stays moist and receives up to six hours of sun each day. Good air circulation around the planting bed is encouraged as Joe Pye weed is susceptible to mildew diseases. Joe Pye weed does not like weed competition, so make your planting area no deeper than 2 feet if planting against a wall or fence or 4 feet wide if planting in beds that have access on both sides. The reason for this is so you can reach into the beds and pull the weeds with damaging the tall, spindly plants.
Remove all weeds and grasses from the planting area. Enrich the planting area with as much as a 3-inch layer of compost worked into the top 3 or 4 inches of soil. Rake the area smooth.
Spread the seeds over the planting area and slightly cover the seeds with a thin layer of soil. It is OK if some of the seeds can still be seen on the surface of the soil. Lightly water the seeds so they will adhere to the compost soil mixture and not blow away. If planting in the fall, they should not need any extra moisture until the next spring or summer when the plants need to be watered regularly. If planting in the spring, do not allow the soil to dry out until the plants are actively growing, then water regularly to keep the soil moist, but not wet.