Fill the seed tray almost full with potting soil approximately two months prior to the last spring frost. Fill a sink with cool water and lower the seed tray down into the water by approximately 1 inch to moisten the potting soil. Watch the top of the soil. When you see moisture reach the top of the soil, remove the seed tray and place it in a location where it can drain.
Spread the milkweed seeds on the top of the soil in the seed tray. Keep the seeds approximately 1 inch apart in the seed tray. Cover seeds with ¼ inch of additional potting soil and lightly spray the top of the soil with the spray bottle.
Cover the seed tray with plastic wrap to prevent the soil from drying out. Place the seed tray under a grow light and strive to keep the temperature at approximately 75 degrees F. Spray the soil with the spray bottle daily to keep the soil moist.
Watch for the seeds to germinate within about one week. Remove the plastic wrap after the seeds sprout. Water the seedlings by lowering the seed tray into water in the same fashion as you did in Step 1. Water to keep the soil moist, but do not make it excessively wet. Keep the seedlings under the grow light the entire time they are indoors to provide light and keep the temperature warm.
Harden the seedlings off to the outside when they are between 3 and 6 inches high. Place the seed tray outside in the afternoon in a sheltered location for several hours and then bring it back inside before nightfall. Over the course of one week, gradually increase the amount of time the seedlings spend outside and move them to a sunnier and less sheltered area each day. At the end of the week, the seedlings will be ready to withstand outside weather conditions.
Prepare a sunny growing area. Milkweed thrives in a planting area that receives full sun. Avoid shady or partial shade conditions for best results. Work the soil with the garden spade down to a depth of 6 inches. Add at least 1 inch of compost to the top of the soil and work this in with a garden spade. Rake the surface of the soil smooth.
Plant the seedlings between 6 and 24 inches apart. Consult your seed package for planting directions that are specific to your variety of milkweed. Carefully loosen each individual seedling using an old spoon. Lift the seedlings under the tiny roots and transfer them to the growing area. Water the newly planted milkweed seedlings generously after planting.
Place mulch around the seedlings to conserve soil moisture and prevent excessive weed growth around the milkweed plants. Fertilize the milkweed plants three times over the course of the growing season by mixing the fertilizer according to package recommendations for the size of your growing area.
Harvest milkweed seedpods in late summer between August and September, depending upon your climate. Watch the developing seed pods and pick them approximately two days before they open. The seedpods should open easily when you squeeze them.