I honestly didn't pay attention to how long the flowers lasted on mine this year. I think they bloomed in early July. I Googled asclepias incarnata to see if there was any information about the length of their bloom period but didn't come across anything substantial. Mine have huge seedpods that are still green--guess I'll have plenty of seeds in a few weeks. The ones growing here were planted 20+ years ago by my mother off the back of the breezeway in the poorest soil you could ever imagine. They come back reliably every year with this much ( ) attention from me. I actually yank out seedlings that come up where I don't want them. I only leave the ones that aren't in my way for the monarchs. This year there were weird, spikey caterpillars on one plant that ate it down to where nothing's left but the stems.

They are not terribly long blooming - I would say a couple/three weeks? However, they are a fantastic plant for attracting Monarch butterflies even when they are out of bloom or are just seedlings. It is one of their preferred host plants. I winter-sow seedlings every year because the female Monarchs love the small A. incarnata plants.

Garedenweed, the spikey caterpillars are the Tussock Moths. They also use is as a host plant. I check over my milkweed plants regularly for Monarch eggs, and remove any and all other insects from the plants and squish them. Not that I have anything against other insects - I'm just trying to remove any predators of Monarch eggs/caterpillars and keep the leaves in tip-top shape to use as Monarch caterpillar food.

All members of the Asclepias family are of interest to me. Over the years I have developed a method to keep them blooming into late fall. This is a family of plants that live to set seed and will continue to bloom until they do unless their blooming cycle is interrupted. Try the following...

Grow Asclepias in garden spots you visit every day as this method requires a few minutes of daily attention. Plant them close together so they form large clumps; suggest four plants to a clump planted seven inches apart. When young blossoms begin to form snip off 50% of them. Allow the rest to bloom and then deadhead the spent blossoms. Do not allow it to go to seed. Every few days check your clumps and pinch off another 50% of the on coming blossoms. The result is large clumps bursting with blossoms which really make a statement in the garden. Or, excellent Monarch butterfly dining. As fall approaches let them go to seed if you wish.

Great advice, nandina. Thanks!