I'm not an expert, but I'll chime in anyway. I bought a p. coriacea on ebay and did something similar. If your coriacea is from the same source, it arrived in a soil mix that is almost all perlite and the pot is only 3" across. My plant went into a quick decline until I started watering it three times a day. Since that stopped the decline, I repotted with a standard potting mix and kept the plant inside under fluorescent light. It took a few weeks, but the plant is now thriving.

Thanks for your comments. It could indeed be the same seller. Arkansas guy? The plant was in great shape when I unpacked it--lots of perlite in a 3" pot. It seemed to have a decent root system--although none or the individual roots were all that big.

I'm not watering it constantly, but the soil's definitely staying moist. I don't want to over-compensate and drown the thing!

I suspect it'd have done fine if I just kept it under a lamp for a couple of weeks as it got established. But the full sun was just too much for it.

Yep, in the last few years, I've bought quite a few plants from dogwooderitternet. He's been great to deal with and the plants have all been very healthy. He's got quite the list of vines that he is propagating and should have up for sale soon.

I bought three vines from him this last time and the coriacea is the only one that I didn't put in the ground immediately. The perlite doesn't hold any nutrients and it didn't hold water well enough for my plant. After repotting it in an almost straight organic mix, I water it every other day and it has tripled in size in the last month.

The other vines have afternoon sun exposure and didn't need to be hardened off. Which is why I think the potting mix might be the true culprit.

On a related note, I checked with Desert Survivors Nursery and they do have P. Mexicana in one gallon pots for sale, if you are still looking for it. I don't know if they mail order though. Here's their number if you would like to give them a call: 520-791-9309.