Ditto. I've made a number of Bargello quilts, and the secret is to use shorter stitches.

You might also try stay stitching around the outside perimeter just outside the 1/4" seam area. This will especially help if you handle the blocks quite a bit. This and shorter stitches should make it more enjoyable for you.

Thanks all!! I'll definitely make some changes the next time I strip piece.

If you have been basting all of your seams you may need to now go back and restitch them, or the whole thing might come apart. Each machine seems to have different settings for selecting stitch length, but, 10-12 stitches per inch should be about the longest stitch for piecing. When paperpiecing or other piecing that requires pulling on seams or cross cutting 12-16 stitches per inch are more secure, likely to hold up.

Just remember the space in between is not a secure as the stitched space. More stitches more secure.

I have found this happens to me if I cut the threads short at the ends of the rows/blocks.

I like a fairly small stitch for piecing and a longer stitch for straight line quilting. I got the idea from sewing clothing many years about. If I mess up and have to unsew maybe it will teach me to be more careful.

Yes, probably a shorter stitch but also make sure you are using cotton thread verses poly which will unravel easier than cotton,

Yes, basting stitch is easy to rip out, but not nearly durable enough for piecing a quilt you will want to last for a long time, through much tugging, washing, etc. Small stitches for quilt piecing... always. You can make them a little bigger for quilting, but not for piecing. No wonder your seams were coming apart.

CKCowl is right--if you've basically basted the strip sets together they may not hold up to quilting & washing, etc. Besides shortening your stitches, be sure to set the seam by pressing before you open up the fabric to press to one side of seam--helps to set the thread into the fabric.