How to piece my blocks with mostly short seams
 

I have a quilt top with 25 blocks which I am sashing. I want to sew it together with only one long row. I'm hoping this will keep it straight. I have already started sewing 4 blocks together in each corner. I'm trying to attach a picture but it won't upload.

I've never sashed one long row. I was taught to sash as I joined the block. Both ways are always straight.

You most likely need to resize your photo so it is a much smaller file size. Most photo viewing programs have this capability.
Regarding sashing, it is challenging to sash the way you describe. The challenge is keeping the blocks lined up on either side of the long sashing strip. Use a ruler and mark the wrong side of the sashing where the blocks are already attached, marking the side of the sashing where the new row of blocks connect. Pin (a lot) or glue to keep them lined up as you piece it. I prefer to use cornerstones but there are situations where you want an uninterrupted sashing. Even in those cases I will often have seams in the sashing and sash the blocks as I go. Peckish posted a great example of how to do that a while back. Hopefully she sees this post and will repost her technique. If you still want a long sashing strip, take your time, mark and pin and you should be ok.

I guess you didn't like my columns in your earlier thread :p
https://www.quiltingboard.com/main-f...s-t307912.html

From what I understand you want and have, this is how I would do the blocks to have only one 5 block seam.

Wow! Thank you so much for taking the time to FTSE that diagram for me! You have some great advice for me! I'm amazed at people's willingness to help on this board! I think your idea will work so much better than rows!

I didn't even mean to start 2 threads on this topic. Lol.

Figured as much, happened (like now) I'm here drinking my coffee and was able to pounce.

Welcome to quilting and the board, glad to have you here and glad to help when I can.

If you do make one long sashing, I would recommend marking where the corners of the blocks should meet it, as if there are cornerstones there. This will keep your blocks in a straight line. It's the cornerstones in sashing that keep everything straight, and without them, marking where the imaginary cornerstones would be on the sashing is an important step.

I don't believe I have ever laid out sashing length way, always top to bottom with corner stones. It can be tricky but going slowly and with practice it fits.

I have. It was on one of my first quilts. Getting everything to line up is difficult. In my case, it was on an I Spy quilt, using blocks I had received in a swap. They weren't all the same size, so it was a really difficult job. I mean row 5 was longer than row 6, so after I had already attached the sashing to row 5, it wouldn't fit row 6 and line up correctly. I finally replaced a couple of blocks on row 6 to make it fit right.

Now, not only do I check that the charms are the right size, I sash each block. It's really easier than the long strip of sashing, even though it doesn't seem so.

If it's too late to change anything, make sure your rows fit together before you sew the sashing on. Then try not to stretch anything as you go. If you can cut your sashing on the length of the grain, rather than across the grain, the sashing will not stretch much, if any. However, if the rows aren't exactly the same size using the width of the fabric will allow you to ease it a bit.

Something I learned from a video: If one row (or block) is slightly longer than the other, put it on the bottom when you sew. It will help take up the slack.

Of course, we're all speculating a solution for you. We don't know exactly what you are trying to do as we have not seen a photo. You say you want to sew blocks on a long row, then you say you are sewing the blocks together in the corners, which seem to conflict to me.