Wow — borders look pretty trivial, but they can be really tricky. If you’re not careful with piecing your borders, your perfectly square quilt center can get dramatically out of square quickly. When sewing on a border that was cut cross-wise to the grain of fabric, it will stretch very easily (especially if you are trying to keep it a little “tight” for an accurate seam) and you will end up with wavy borders. If your pieced quilt and your border do not feed in at equal rates to the machine, you will have an unsquare border. The more borders you add, the worse it gets. This has bad ramifications when you take your quilt to your friendly long-arm quilter, as the quilt frame is square — if your quilt is out of square, you will end up with tucks, folds, or inaccurate quilting. For computer systems, that depend on square quilts, this can be death to an accurate border stitchout.
I know that the “traditional” method of adding borders is to measure the dimension of your quilt at three places, average the lengths, and then cut the border to that length and ease in. I’ve tried it; it doesn’t work well for me. No one else I know uses this method, either. Here’s one easy way that will give you square borders with a minimum of hassle.
Cut your border fabric to slightly longer than the quilt edge you’re going to stitch it on to — say 2-3″. Then lay the border fabric on the floor, right side up. Center the quilt (right side down) on the border fabric so everything perfectly aligns. Pin (yes, sorry, you do have to pin; I hate it too) the border to the quilt top, say every 6″ or so. At the edges of the quilt, also pin the border to where it meets on the inside of the quilt (that is, you’ll have a u-shape of pins once you’re finished). That way, when you pick up the quilt, the border won’t flop away from the quilt. Stitch on the border. Then, without removing those extra pins that you pinned the border to the inside of the quilt, take the quilt to the cutting board, verify that the quilt center is still square, and cut off the excess with a rotary blade and ruler.
Because you pinned the border, you don’t have excess fabric that will pull you off-square. You don’t have to measure and ease-in a variation on length. This has worked well for me — try it!