I don't think that you can mount them upside down. Even if it was, any new growth will right itself naturally as it grows. Some staghorn ferns are much easier to distinguish between which side should be facing up. For example, I bought a dwarf Platycerium superbum 'Cabbage' last year. It was still fairly small, but you can clearly see which side should be facing up...

But as for the ones typically sold at Wal-Mart, the Platycerium bifurcatum, they're a little more lax on which side should be facing up, because they can send out growth in any direction. I mounted one of these a couple of years ago. It had two main growth points, so I just mounted it with them side by side. Don't worry about damaging the shield fronds because newer ones will emerge and cover the older ones up. Back when I first mounted mine, it didn't have any basal shield fronds whatsoever, but it eventually began to grow some towards the end of the season before I had to bring it back indoors for the winter.

Also, when I first mounted it, I removed most of the soil that it was originally grown in. My staghorn seemed to suffer a bit from this, because it would dry out so quickly. But this past year, as new basal shields were growing out, I kind of lifted the tops of them and sprinkled in a bit of cacti and succulent soil. Just so that there would be a little something to hold on to a bit more water, just long enough for my staghorn to soak up what it needs before it dries out again.

Well, after reading all of this, I feel a little reassured. I thought that it was a bifurcatum after some research, thank you for verifying that. So basically, I'm just going to continue on my current route and let it rebound from the mount. Hopefully it will bounce back better once I can bring it out in the humid air of our summers. My orchids love the humidity we experience here, I'm sure the Platycerium will do the same once it has the opportunity.

I live roughly on the borders between zones 7a & 7b, and it gets very humid here as well. Both of my staghorns, my orchids, and all the rest of my plants love it during the summertime. I'm sure yours will too. Yeah, I don't think I've seen Wal-Mart sell any other species of staghorn fern, other than the bifurcatum.

As I thought about it some more, I remembered that their staghorns are grown on their "side," so to speak, as opposed to how they grow naturally in their native habitats, mounted to the side of a tree facing outward. So they don't really have a definitive up or down, yet, until you mount them. Even then, they continue to grow and spread out in every direction as new pups emerge. So whichever way you've mounted it, it really couldn't care any less.

Other varieties are more distinct, such as the dwarf 'Cabbage' that I purchased last year. I'm sure that they would fare much better by being mounted facing the proper direction. I quite look forward to seeing it fully mature. This isn't my photo, but it provides an excellent example of what it'll look like...

I haven't mounted it yet, but for now, I've brought it back in for the winter and have it growing under a grow light to kind of give it an extra boost until this coming spring.

I looked up the Cabbage cultivar when you mentioned it, it is truly interesting. I believe I would've named it Butterhead Lettuce though :). Regardless, good luck on raising that one, it seems as if it would look like a great addition to a collection.

Yeah, I mounted mine sideways also. That is why I found this info and hopefully my platycerium bifurcatums is ok.