Certainly you can plant and grow tropical here, just understand that they will die in winter. Asclepias are an annual and will have to be replanted anyway so it's really a moot question. Just save your seeds.

Off the main topic, but on the subject of milkweed be careful when handling to not get get any sap in your eyes. << This is one person's experience.

Interesting link and comments; first I've heard tropical milkweed might compel more late fall breeding than the natives. Certainly something to look into beyond the couple anecdotal cases; I'm not yet convinced that the problems are that significant in places like north Texas where all milkweed usually dies back by the second half of November. The Potential risks of growing exotic (non-native) milkweeds for monarchs fact-sheet from the Monarch Joint Venture provides a great overview and guidance that's pretty much in line with what has already been mentioned above.

Texas Butterfly Ranch also posted a bit of the differences from Glassberg's perspective at: Tropical Milkweed OK for Monarch Butterflies, "Just Cut the Dang Stuff Down".

If you can get or grow native Texas milkweeds, good for you! Always good to use the plants native to your area. But if not, don't worry, Tropical Milkweed is native to Mexico, which is our neighbor, not far away. There's been a lot of BS printed about Tropical Milkweed, which is unfortunate. The Monarchs are in a big crisis and have decreased in numbers dramatically. I blame Neonicotinoid pesticides, genetically modified crops, Round-up ready crops that have wiped out milkweed in huge areas of agricultural fields, severe loss of habitat...both in the U.S. and Mexico. The fact is, we need to provide the Monarchs with more milkweed (their only host plants) during the times of year when they are here to reproduce. Also, the Monarch butterflies and especially the caterpillars are sensitive to pesticides and every bit of restraint in that matter makes a huge difference. There's been a groundswell of demand among those who want pesticide-free milkweed to find a reliable supply. But still, most nursery milkweeds being sold have systemic pesticides applied at some point before being offered to the public...systemic pesticide doesn't wash off and will kill the caterpillars. And I might add, if you go to nurseries to buy milkweed, you're unlikely to find any milkweed except Tropical Milkweed. Now, in the town of Medina, there's a nursery where you can find native milkweeds that are safe for Monarchs. It's called Medina Garden Nursery.

http://medinagardennursery.com/about-us/

Or you can get seeds and grow your own milkweeds. I've had Monarchs come by three times this year and lay eggs on my milkweed here. I have native Texas Milkweed and Antelope Horns, which are perennials. There are many native Texas milkweeds...they're just harder to get. I also grow Tropical Milkweed and have never had a problem with Monarchs lingering to spend the winter here. It is an annual in most of the country, but can survive winters when temps don't get very low. Since I live in the hills where it's a bit colder, they will often die here if not protected. I haven't seen any Monarchs yet this fall, but the peak month for fall migration is usually October, so they're probably coming through. There's just much much fewer Monarchs than there used to be, so you might have to really watch carefully to spot any. They need our help. The Monarchs that are just passing through headed to Mexico will need to stop and find flowers for nectar, food to help them on their way. There are also usually some reproductive Monarchs headed our way in addition to those. They will use milkweed to lay their eggs on. That way, any of their caterpillars that survive and become butterflies will increase the numbers of Monarchs that head to Mexico to overwinter.

https://monarchbutterflygarden.net/raising-monarch-butterflies-ebook/http://www.washingtonpost.com/news/wonkblog/wp/2013/12/03/why-are-the-monarch-butterflies-disappearing/

http://www.cbsnews.com/news/monarch-butterflies-drop-migration-may-disappear/

http://www.monarchwatch.org/

I planted a monarch/butterfly bed this year in our community garden. Saw my first monarch last week and one monarch caterpillar chomping away on the antelope horn milkweed that I had transplanted. I've done a bunch of reading on this and I agree with the comments above: I will cut back the tropical milkweeds after our first frost.

argh.....wish i hadn't read this as i have a ton of tropical milkweed (which seeded itself) i probably have more than a hundred 3/4 grown plants i do live in zone 9b but i'm not sure that helps enough....

in studies the monarchs always prefer the tropical milkweed. I do not have any problem with it here and it does not freeze back and often blooms all winter. I am 9b also. I will continue to plant it.

it's my very best "reseeding" plant and my best aphid "catcher"

I have Milkweed growing in my front yard garden. At this time I don't need 25 plants growing so currently ripping it out and hopefully it doesn't come back. I don't mind about five plants growing, just not so much that is out their right now.

I was not able to get to the seed pods last year as we were on vacation. I also have been cutting off the seed pods & do have seeds if anyone is interested. I will send them to you & I will even pay the postage! Anyone interested??

yes! I buy butterfly weed constantly and it gets eaten to the ground.