Applying borders properly is a crucial step in completing your quilt so that it has a finished look and it lays flat and "square". I have a few tips to help you achieve this goal. Often new quilters will simply cut a strip longer than the side it is being applied to, then sews it on and cuts off the excess. It sounds logical, but it creates a myriad of potential problems.This method usually results in wavy and uneven borders.
1. To begin with, make sure the body of the quilt is "square". Meaning that the length of the quilt is the same on the left side, center and right side. If you have been careful with the piecing, it should be close. This also applies to the width.
2. You always want to measure the 3 places along each direction. If it is slightly off, you will be able to ease in the fullness with the borders. The difference in the measurements is usually due to stretching of the fabric on the outside edges. If it is significantly off, you will need to re-evaluate where you went astray with the piecing.
3. Once you have the 3 measurements, you can either use the center (usually the shortest measurement) or take an average of the 3 measurements (fig. 1). If the center measurement is 1/2" or less, use it. If it is greater, then use the average. Once that number is determined, cut two borders that length. Pin them to the opposite sides of the quilt matching ends and center easing in the fullness. Use lots of pins. Sew and press.
4. Repeat the above process with the other two borders, including the borders you have just sewn on in the measuring process (fig 2). Press. The above procedure is for simple blocked borders.
5. If you want to add cornerstones, you simply add them in the corners, but remember to do the measurements first!
6. If you want to miter your corners, this procedure still applies for the length of the border attached to the quilt. Leave at least the width of the border extra on each end and use a 45 degree ruler to mark your sewing line so the corner comes out square.
7. Here you can view my video of how to apply borders: