Help with piecing backing
 

My backing needs to be 74 in. X 91 in., this includes the extra 3 in. on all 4 sides.
I have 7 yds. X 41.5(minus selvedges) WOF to use.
I would like to preserve as much as much of the backing as possible for the quilt coming up next.
If I cut 2 pieces at 2 yds plus 19 inches(=91)
I'll sew a 1/2in. vertical seam this will make the backing width 82in. (41.5 x 2-1=83)
My questions: when do I trim the excess 9 inches?
After I have joined the 2 pieces? Or Before?
Trim 4.5 inches from each side so seam is in the middle?
Trim 1 -9in piece from one side making for a seam that is off center.
The backing is beautiful fabric, soft yellow, tone on tone. I really don't want to mess this up!!
Any other possibilities to piece?
TIA, Jo Anne

I use whatever left over fabric I have from the front. My backing is never one color. It is made up of fabric from the front.

I figure out how large the back needs to be. Then I lay down my pieces of fabric and sew them together until I've made the size that I need to create the back of a quilt.

I would trim the 9 inches off one piece of fabric before joining and have an off-center seam. I'd rather have one 9 inch wide piece of fabric than two 4.5 inch wide pieces.

gingered, Beautiful backings!
I have in the past pieced backs from leftovers from the top too and do like the look. For this quilt top I don't have enough fabric left over worth adding to the back.
Indycat32, A 9 in. piece would be my preference too.

I'll add another variable ... wait and trim your nine inches after your quilt has been fully quilted.
That way, your nine may soon become ten, eleven or maybe even 12", by combining that nine with the narrow trimming piece that would be left once trimmed. Bonus! you can accomplish your goal of keeping as much fabric as you can.

When I do backings, I leave the selvage on the outside edge on (when possible), to help prevent fraying. Plus it gives a good solid edge when working with the backing, whether to sandwich on my tables or for the LA'er. If you are having your quilt LA'd, most would prefer that the seam be horizontal, rather than vertical. Best to check about this with your LA'er. Each has their own preferences or restrictions.

I have lots of large yardage pieces, therefore I try to not have to piece a backing unless I use the same fabric. I don't like to piece backings unless it is for me.

Since I mostly make donation quilts now for kids I usually don't have to piece to make them big enough.

It goes to the Long Armer Feb. 16th. Ironically, it was an employee at the LQS that suggested the vertical piecing. I just emailed the L.A., see what she says. It would be wonderful to have 10-12 in. for the next project.

I don't like vertical seams on my longarm set-up, as they will create uneven and baggy areas when rolling up. But this is OK if I can put the quilt up side ways. Also I wouldn't cut the 9" off before quilting 'cause you just may end up with a 12" strip after, ( you will have that extra 3" all around to trim that won't be quilted). Hope that's a bit clearer than mud

I agree with indycat and have 9 inches left. You may need this for the binding.