I have grown this plant and yes it is the tallest milkweed I have grown. They do not overwinter as well as I had hoped and maybe it is because I let them get the seed pods. This year I plan to remove them.

Looks like we're in the same Sunset zone. How wide did your plants get? What do you mean by them not overwintering well?

They were more tall than wide. I'm in the Napa Valley and we get winter freezing. They died. The ones I kept in the hot house survived tho and I took cuttings off them. The cuttings are doing well.

Very helpful, thank you!

I'd planted two from gallon pots in the past and had them die. Now I have maybe 7-8 from seed and I'm being careful with them. They are in good soil in half barrels and in mostly full sun, doing well, about 3 ft tall. The only one I've seen elsewhere was at a nursery in Seal Beach, full sun, large pot, about 6 ft tall and maybe 3 ft wide. Full size, I believe and covered with seed pods.

Mine are still in the 1-gal containers I bought them in and are just shy of 4' tall and blooming. Must get them in the ground!

Looks like A. physocarpa doesn't get 6' wide anyway. This will help me on spacing. Thanks!

Thought I'd update --

I now have 8-10 plants that are two years old. These grew from seed of the original 1-gal plants that I bought. The largest is 6'-7' tall, 5'-6'' wide with multiple branches. The rest are slightly smaller. They grow in clay soil; the largest in an area that I've amended, the rest in unamended soil. They have been blooming for a couple months and have some mature seed pods but are still setting flowers.

Last year (their first) two plants were beset by aphids, ants and sooty mildew. I took to washing the leaves (especially the undersides) daily to keep on top of the aphids. I watered occasionally.

The plants overwintered very well, never losing their leaves, though we only have light, occasional freezes. Very little rain this last winter (~9"). I have given no supplemental water this year and the plants seem to be well established. No ants/aphids/sooty mildew. There are a plethora of boxelder bugs on the milkweeds but they seem to do no harm to these plants or any other.

Last year I had many monarch cats on the plants but haven't seen any this year and I haven't seen monarchs flying around either. Not sure what that's about.

All in all, this is a beautiful, carefree plant! I think it should be more widely grown.

I have speciosa and prefer it. But grow many milkweeds. Last year had no monarch and this year is alot better. One group is grown and a female was checking things out today so may be more. Eggs mostly laid on Narrow Leaf Milkweed however. I have 7-8 kinds.

Penny

I grow them next to the sidewalk and once the pods form I enjoy seeing the reaction I get from passersby. Quite humorous.... I have never seen cats on mine, I also have many Asclepias curassavica growing as well and the Monarchs that live here year-round prefer those.

The A. physocarpa tend to be lanky with few branches compared to the A. curassavica which is bushier and more colorful.