Why BMI Is a Crock, in Pictures. So, the Guess The Rotund's Height and Weight game gave me an idea. (Oh, and hey, if you want to see a scatter graph of the results, there's one here now.) I talk a lot about how BMI is bullshit, but we all know talk is cheap.
As suggested in the above links (Thanks! ShellaB, for posting those links -- The first one was especially useful.), you can use monofilament plastic fish line to tie the fern to the basket, if needed. I stuffed my staghorn's basket with a combination of leaf litter, spaghnum, and Spanish Moss.
A slow-release fertilizer can be used if placed on the organic substrate of larger ferns in small amounts. Some recommend other organic material be placed there as well. For some reason (the potassium, perhaps?) banana peels are frequently recommend.