you seem to want a general rule for all MW.. and i suspect .. being that there are a lot of variations on the theme.. that you cant generalize ...

i have milkweed all over the property... self sown.. i dont know why you are bothering not to do the same.. sowing directly ... especially in TX where you really dont have what i would call ... a winter ....

dont forget to harden them off to direct sun... and i would probably do it in winter .. when the sun wont be as severe as summer sun down your way ..

ken

Some milkweeds can have deep roots. Common milkweed is noted for it. But not all milkweeds have deep roots, different kinds have different depths noted. Zizotes is noted for shallower roots.

Well, OK then, generalizations about milkweed roots and difficulty in transplanting aren't accurate. But that's useful to know that Zizotes has shallower roots. I have a small package of seeds. I'm not just going to toss them on the ground and hope for the best. In fact, Monarch support orgs recommend starting milkweed under lights. Once I get this stand started, presumably they will self-sow to fill in the gaps.

Milkweeds put on a lot of root growth, right after germination, so it's best to start them in a container that allows for root growth, and not the small cell trays. They are also dependant on macchorhizae, so I recommend either a potting soil that contains maccorhizae or adding it to the potting soil. I grew zizotes milkweed for a couple years in northern Illinois, and then it fizzled out, but Asclepias fascicularis and Asclepias subverticillata both are able to overwinter here, and their agressive rizhomatous nature might be the reason. They get kicked back in winter, keeping them in check. The Monarchs seem to prefer laying eggs on the A. subverticillata, because it still has fresh green leaves, when A. syriaca is getting shabby looking in late summer. Asclepias incarnata and Asclepias texana have shallow, fibrous roots also. It's a good idea you are letting your's get larger before planting out,

I had them in 9oz cups, and when I planted them out, they were two inches tall. There was no evidence for being root bound in those. But when I pot the new ones up, I'll make sure they have plenty of room down below.

9 inch cups is perfect. Zizotes can tolerate gravelly soil. Here's a few pics of Texas milkweeds Ive grown in Illinois.

Narrowleaf Milkweed, Asclepias fascicularis

Wooly Showy Milkweed, Asclepias speciosa

Engellman's Milkweed, Asclepias engelmannii

Antelope Horn/Spider Milkweed, Asclepias asperula

Texas Milkweed, Asclepias texana

Zizotes Milkweed, Asclepias oenotheroides

Horsetail Milkweed, Asclepias subverticillata.

Ah, wonderful. A milkweed expert! They're going into pretty good soil that is at least a foot or two deep. Lots of organics. MIght be rocks below that. They'll get a few hours of sun, which I've heard is all they really need. I gather they're pretty drought tolerant. This site doesn't get a lot of water in the summer.