A few measurements to start – my finished cushion front is 50cm square and the zipper was 46cm. I had tried a longer zipper, but that caused a bit of grief with the binding. The instructions from here on should work equally well no matter what size your cushion.
First I trimmed back the wadding and backing to the edge of the front. Then I made the binding. I use Canoe Ridge Creations binding method outlined here. The only difference was that I used a 2 1/4" strip for the cushion binding.
Now, because you're going to be inserting a zipper here, you don't also want to deal with the ends of the binding in the same spot, so use the middle of the binding strip and pin it along the edge you want the zipper on (I chose the side of my cushion).
|Left: Pin the back to hold it in place.|
Right: Turn the cushion cover over again and sew the binding around the remaining three sides.
Use a cushion two sizes larger than the size of your cushion cover, and your zipper should stay hidden just so!
Just one more cushion to go and then I'll have the patterns up for those as well.
Happy Australia Day everyone!
PS Oh and thanks to everyone who voted for my Spring Patchwork! It got voted about 48th in over 250 votes and was featured on Spoonflower's recent trends page. Pretty happy with that :-)