I have Asclepias speciosa; 3 feet tall and which can spread underground to cover a large area, but is easy enough to contain by pulling out the stems. No caterpillars yet in 5 years.
I also have Asclepias fascicularis; much more petite, under 2 feet, and has not spread in 2 years. Also have not detected any caterpillars :( We do get the occasional Monarch here in Los Gatos.

I grow tropical milkweed (A. curassavica) and narrow-leaved milkweed (A. fascicularis) here in SoCal. I haven't had the native narrow-leaved long enough to learn its invasiveness level, but it does go dormant in the winter.

The tropical tends to have seedlings sprout around the garden, but never to the level that it is not easily controlled. Trimming the plants prior to seed dispersal would be an easy method of control. I like the seedlings, because so many Monarchs visit me that all of my plants get stripped bare. I sometimes have to move the cats around to better patches so they don't starve.

When we moved, I brought two tropical milkweed plants from our old garden. The Monarchs found them within a few months. Although I have not seen other gardens in my neighborhood with milkweed plants, I suspect the abundance of nectar sources may have already been a draw.

I also grow a. curassavica and have had tons of Monarchs and caterpillars for years now. The curassavica does not seed excessively and as said above, I need every seedling / plant to feed the cats. I had read previously some few years ago that a. curassavica is not as good for the cats...can give them 'indigestion' and so have been aiming at growing large stands of natives...so I'm wondering about the fact that your natives have not drawn any / many monarchs. Recently I've read that the stating that a. curassavica is not good for the cats is false....

In any case, if I'm growing asclepias for the monarchs, I certainly do want it to spread as much as possible, because once you have the Monarchs there, you will have a lot of them and they need a lot of help....

We have the narrowleaf milkweed in this area, one of the few natives that are left. The first year we were here I observed what looked like a giant winged ant on the milkweed. I tried to get close to it with my camera so I could ID it and found it did not like me getting too close. I got enough of an picture to see that it was a Tarantula Hawk, the sting of which is considered the second most painful insect sting in the world.

Luckily for me, it is not an aggressive insect, but nontheless, I've discouraged the growth of it's favorite meal (narrowleaf milkweed) in my vegetable gardens and sitting areas. I let it grow in the wilds of our property.

I have grown the native milkweed, which spreads pretty aggressively (tried to grow it in a whiskey barrel and it grew through and into the soil) and the pretty red tropical milkweed, which goes to seed easily. I could not keep up with the deadheading of the tropical variety, and the sap is very, very bad for your corneas. Since I seem to always be rubbing my eyes (and getting everything from sharp sticks to oleander sap into them) I thought it would be prudent to get rid of the tropical milkweed, since it took a lot of time to trim off the seed pods before they sent seed all over my yard.

I love all milkweeds, though, and if I wasn't such a dork about getting things in my eyes I would still grow it.

Always something new to learn. I've never heard of a Tarantula Hawk and don't rub my eyes around the milkweed.....going to go look up a picture of the Tarantula Hawk.

Bravo on all milkweed growers! Here's a link (that itself also contains other links) with more info.

Kay

Here is a link that might be useful: Milkweed and Monarchs

Thanks so much everybody. The tropical milkweed seems like it would be an option, only it sounds like it attracts neighborhood cats. I definitely don't want to do that because I grow herbs and veggies and am paranoid about eating things that the cats have urinated on... maybe that is my dork moment. I really want to grow it but I always get deterred by its invasiveness!! I'm going to have to give it more thought. Thanks again.

I have about 8 varieties of milkweed, narrowleaf, tropical, speciosa, Davis Ca speciosa, Texas, Koholo and afew others. Monarchs are not as plentiful as they once were, but other insects enjoy the milkweed and some I love the flowers. I take root cuttings of some and move them into new places. I also have the swan milkweed, after it seeds, it dies down however I spread the seed around. I have the area I can do that. My first monarch cats were on 9-11 (the bad day) and it has not spread that much in the years since. Just dig and move. They transplant easily.

Huh. There are a number of neighborhood felines that visit my garden, and pass through it during their wanderings, but I have never seen any of them show the least interest in my tropical milkweed. Occasionally one might eye a hummingbird visiting the milkweed flowers, but that isn't quite the same attraction. ;-)

I don't think cats are drawn to asclepias...however...*cats* as in caterpillars are......

I found some Asclepias Tuberosa seeds....do I plant directly into soil, or do they do better in pots to transplant. In the Inland Empire. I don't have full sun, lots of palm trees, so hopefully I can do something to help the butterflies!