I design my stitching patterns to fit on a standard size double-fold card. These types of cards may not be available locally to you, particularly if you live outside of the UK. There are other options and the results can enhance the design in a creative way.
A double-fold card has three panels. The right-hand panel folds in to cover the back of the stitching work and hide it from view. This third panel can be fixed in position with double-sided self-adhesive tape or stick adhesive to make a quick and neat finish to the stitching. Double fold cards are made by several manufacturers in the UK.
An alternative to the double-fold card is to stitch on a separate piece of card and mount this on your greetings card to hide the back of the work. It can be fixed in place with double-sided self-adhesive tape or stick adhesive. Self-adhesive foam pads can also be used to mount the card to give it a slight lift. These pads are used in decoupage work and should be available from shops that sell decoupage sheets. When mounting this separate piece of card you could use a contrasting colour on the front of your greetings card or cover it with a patterned paper.