How to avoid wavy borders
 

This wall hanging has been a nightmare. First my back bleed red to front. Then ripply border. I eliminated border but still wavy. I know it is caused by my quilting but how to I avoid it next time? How do I add a photo

Just make certain the border are the same length on opposite sides. It sounds easy, but it's not. If there is too much border, long may they wave. Of course if it was a quilt instead a wall hanging, I would just say, throw it on the floor. Which is where mine seem to end up. They are seldom folded. I have helped wall hangings straighten by hanging a rod on the bottom also. It "pulls" it down by adding weight and keeping it semi flat.

Press your top as flat as possible.
Measure the width in 3 different places, keeping away from the edges.
Write down each measurement and add them together then divide by 3, that is your average and that will be the size border to cut.
Repeat this same step for the length of the quilt.
Pin from the center out.
Cut length of fabric when possible, this helps avoid the dreaded bias.
Starch is also your friend.

What technique did you use to add the borders?

I stay-stitch around the quilt edges before quilting and then press. I also stay-stitch and press all borders before adding them to the quilt.

Sometimes I mark along the quilt edge in quarters and the borders in quarters. Match the marks on each and pin together.

I have the quilt on top of the border strip to sew not the border on top of the quilt. The foot acts like a plow on the top fabric pushing it ahead. I don't need my border strip being pushed longer. This works for me. I don't measure I sew on the border strip then cut to size. If I have any wave it is easily taken up in the miter corners.

Donna Jordan has a great YouTube video on making borders and how to ensure they don't turn out wavy. She recommends measuring the border not on the edge, but closer to the center of the quilt. Here's the link to the YouTube:

(2) HELP!! Borders??? EASIEST FANCY BORDERS FOR ANY QUILT!!! - YouTube

It sounds as if the problem is after you quilt it?
quilting often skews the quilt, which is part of the reason your backing and batting are larger than the top before quilting. After quilting you square up the quilt then stay stitch all the way around the quilted sandwich about 1/8” before adding the binding.

or, is it just the borders, before quilting?

Natalie Earnheart has a wonderful video (Missouri Star Quilt Company, or YouTube) where she explains how to square up a quilt when trimming the edges before binding. It has helped me to have less wavy edges on my quilts. Apparently I wasn't trimming things correctly and that was creating some of the problem.

I never measure the sides of the quilt - I lay the border fabric down the center of the quilt and cut it to that measurement. Then pin it on and sew it. No wavy borders! https://cdn.quiltingboard.com/images/smilies/smile.png