I don't have the answer to which asclepia, but I did find some tropical milkweed at local nurseries in Central TX. The nurseryman said the tropicals are annuals but reseed vigorously.

Round Rock Gardens, Round Rock TX, yellow tropical milkweed
McIntire's Garden, Georgetown TX, bi-color milkweed, orange & yellow
Natural Gardener, South Austin on Bee Caves

Hope the info helps.

I've been to Natural Gardener, but not this year. I'll have to give them a try before ordering online. Thanks for the info.

There have been studies to answer this questions. However, there are some 70 plus milkweeds in the united states and all were not tested. It may differ in different parts of the country. The studies and our experience says that A. incarnata seems to work the best. However, it is a wetland plant and may not work well in the dry heat of Texas. You might contact someone in your local butterfly club and see what works for them. A. tuberosa likes drier conditions but the caterpillars have to injest almost twice as much materials to equal the same amount of A. syriaca or A. incarnata. I would vote for A. curassavica, the tropical. It is easy to raise and come back well from being eaten. They really like it too. However, it is not native and may be invasive there so be careful. Look for native milkweeds. There are several websites that sell them such as Prairie Moon. If you go to the USDA Plant database you can click on the Asclepias section and it will show you all the native Asclepias and you can figure out which ones are native in your area.
Cheers,
Elisabeth

I second Elisabeth's thoughts, with a small exception.

I kept track last year of which milkweeds got the most eggs. A. incarnata won out over A. tuberosa and A. curissavica by a 3:1 margin or so.

The "small exception" is this: I have the incarnata planted on a hilltop. With reasonable water, it does fine -- I had to water only once last summer, but it was a wettish summer. So wetlands are not strictly necessary.

That said, A. tuberosa seems to be a bigger favorite for the hairstreaks as a nectar plant.

Jeff

This is true Jeff. A. Incarnata does not need to be in a swamp. I have it on a north side of my house and never water it. I will say this though. It will be subject to more disease if kept dry, such as powdery mildew. There are probably other milkweeds that Monarchs like just as well for the dry dusty of Texas. At least that is how I imagine it being a yankee and all :)!
-Elisabeth

Reports from other Texas gardener's indicate that A. curassavica and A. physocarpus (Swan Milkweed; Family Jewels, Hairy Balls, etc,) are very popular milkweeds with the Monarchs. Both do exceptionally well here in Oklahoma as well. They are not hardy for us, but may be for you. At least you can collect the dried seedpods for planting next spring. There is another milkweed similar to A. physocarpus called A. fruticosa. It is similar in growth but is smaller in comparison to A. physocarpus, and I don't think, but don't know for sure, that it produces the same type of seedpods as A. physocarpus.

In doing my search for photos of these plants, I came across Goodwin Creek Gardens, and they are offering plants of A. physocarpus for $3.00 each, on sale right now. They are in California, I believe, but I know MissSherry has ordered from them (not milkweeds, right?) but I think she has been pleased with the plants she has received from them. Mail order plants are usually very small, in 3" or so pots. However, the ones I have mentioned are very vigorous milkweeds and will grow quickly. That's a pretty good deal. There is always a risk when you order plants "sight unseen", but I am one who is willing to take the risk. But not everyone is, and that's okay. It is very possible you will find something locally.

I attached a link to their site so you can look at a photo of the flower of A. physocarpa and if you click on the name "Asclepias physocarpa" you will get a photo of the seedpods.

Susan

Here is a link that might be useful: Goodwin Creek Gardens

I can attest to the fact that A. physocarpus is quite vigorous. I started two plants from seed this year and have had them planted outside for the past two weeks. Mama Monarch has already laid two eggs on one of the plants. They are beginning to put out new leaves on top as well as side shoots from the leaf nodes on the single trunks and appear to be quite healthy, robust plants.

This is my first experience with this plant and I think it's going to work out real well in my location (central Arkansas). My only concern is finding space to grow them.

Mary

swamp milkweed[asclepia incarnata] is great.tropical is very good also and needs very little maintenace.just have room for them because they grow fast.

I've been happy with the plants I've ordered from Goodwin Creek Gardens, although I haven't ordered too many from them. They have a good selection of salvias, and the ones I got ordered have all come back and are thriving, especially the S. microphyllas. I'd recommend them.
The butterflies around here love to nectar on my A. curassavicas and much prefer laying eggs on it to my honeyvine - they've never used the little bit of A. incarnata I've got here for egg laying. Maybe they just don't use it because they like more and bigger plants.
My 'family jewels' plant limped through about a week, then died when it rained, even in a raised bed - I think it likes lower humidity and less rain than we have here.
Sherry

Here in North Texas, I usually grow tropical from seeds. I have an envelope with some more tropical if you want to send me a PM & a SASBE, I'll send you some. I also have planted common & swamp milkweed this season for the first after cold stratifying the seeds in my frig. We'll see how they tolerate our hot Texas summers! I have some left if you would like me to include some.
Just send me a PM & I'll send you my address. All the BFs here love the red tropical!