Scientific name: Asclepias syriaca
This stuff has been growing to almost 6 feet in height, and spreads readily. It has also attracted an entire apiary to our garden. There looks to be at least two bumble bees for every flower, and the perfume-like aroma is strong.
Tip: you can let them grow to about 3 feet, and before they flower, cut them down to about one foot – you’ll still get flowering plants, but they won’t grow to the towering height. Just be careful not to get the milky-white sap in your eyes (speaking from first-hand experience). I also understand that it can be a skin irritant, but it didn’t seem to affect my skin.
In addition, it’s recommended you plant other tall things with it (like mountain mint, joe pye, or scarlet bee balm) to prevent the tall, heavy stalks from toppling over or sagging. If they do topple over, that’s okay, they’ll continue to grow.
Bonus: even the most desperate of deer won’t eat this this stuff.