Both a long lived perennials. Asclepias incarnata is best for moist soils and A. syriaca works in any other situation. The latter spreads quite a bit.

"Spreads quite a bit" is putting it mildly. When I grew it, new plants would pop up ten feet from the original plant. That was in a large, mulched garden bed. They don't compete as well in heavily established meadows or other thickly planted or deeply rooted areas.

Martha

I've always had problems with A. incarnata dying off after one or two years. I keep planting it because it is the best.

KC

Mary, that is a great idea! I may do that with a bunch of five-gallon buckets I have sitting around. I wonder if you could line a hole with landscape fabric to prevent them from spreading beyond where you wanted it? Though, I hate finding that fabric in the ground, since it is so hard to work around. I live in a neighborhood where having buckets sitting around wouldn't be acceptable to neighbors (or my husband).

Martha

Martha,

I don't know for certain, but I doubt the fabric would contain the spread. I tried using that with Maypop and the roots went right through it.

I've recently planted some new Common Milkweed seedlings in ground next to my greenhouse as I'm curious to see how bad the spread might become in future years. Seems like just pinching back the new growth that has spread into an unwanted area would contain the plants to areas where wanted. Maybe it's worse than I envision. If so, I will use cotton balls, soaked in Brush killer, placed onto the plant stump and covered with a plastic baggie held in place with a rubber band to kill off the underground roots.

Perhaps your husband wouldn't object to a pretty, large flower pot, such as you might use on a deck or patio, to grow just two or three plants. Maybe try burying one bucket in ground and see if that would contain the plants. You could hide the rim with mulch. The real benefit to growing Common, of course, is the leaf size. Those big leaves will feed a lot of little cats.

Mary

Fortunately, I just realized that or neighbors have A. syriaca growing up through their evergreen shrubs, and they are spreading into our yard! Oh, that's just so too bad! Can anyone sense a bit of sarcasm? They are lovely, healthy plants, too.

My A. incarnata also continues to push up more stalks each year, and I keep planting more varieties. This year I have A. speciosa and another I can't remember off hand. I also have tons of mature A. tuberosa and new sprouts. And, as I wander through the garden, there are quite a few volunteer A. incarnata seedlings coming up everywhere. I think I have all the milkweed I need. In addition, there are two large patches of syriaca within easy walking distance of my house. All I need is a Monarch female with a gut full of eggs to visit.

Martha