I always order a few extra bunches of leather leaf fern. It is invaluable for filling in open gaps in the design for a very reasonable price.
I am a little astounded, however, that some wholesale flower farms insist that a DIY bride purchase a minimum of ten bunches. That is a LOT of greenery!
In my area of the U.S., leather does NOT retail for $150 for 10 bunches. (By the way - leather typically sells in 25 stem bunches- not 20). I would never pay $15 wholesale for a single bunch of leather leaf fern.
Retail is typically $6.00 to $8.00 a bunch (what they are saying is the "wholesale" price). Keep in mind that if you are told "shipping is free" . . . it probably isn't. That cost is figured into the final price somewhere!
Buy your flowers and greenery in single bunches. This allows you more of a variety and you can buy only what you need. The price per bunch may be a little higher, but you'll end up spending less without huge amounts of wasted greens or flowers left over.
Leather leaf fills in open spots quickly.
Fan it out behind other greenery for a full rich look.
I typically finish the backs of my church florals so they can be transported to the reception hall for "double duty". This way if they have to stand on an open table, the back still looks finished.
Don't go overboard, but fill in enough that you don't see the florist foam.
Hiding the mechanics is the mark of a professional looking design when you are finished.