Fern invitations are designed to be hand folded. They are delivered flat, with pre-creased horizontals, and printed marker points so you know where the rest of the folds should be.  You (and a pal maybe) can sit down to fold + address them together. Perhaps crack open a beer while you work ;) And then get that satisfaction kick when you have a neat stack of coloured invitations with their spines in order. 

The instructional video below should help you with the first few until you get the knack.  And here's a PDF of the instructions in diagram format too, if you prefer static instructions.

Happy Foldin'  

Folding Tips

Line up the corners first. Then fold from the middle out towards them. You're more likely to get an even, level fold this way.

Fold well + reinforce your creases. You can do this with a smooth edge of a plastic ruler, the back of your thumbnail, or you might want to get one of these handy bone folding tools.

We recommend adding on a few spares when you place your order.  Just so you can have a few practice folds and won't be in a flap if you make any mistakes. 

Our hands, the most beautiful and precise instruments that were ever created, are apt to be neglected. This is a button-pressing age in which the thumb rivals its more sensitive neighbours, but all those who get the most pride and pleasure from their work, still rely on their hands.
— Roy Campbell