I would go with a 4" green border And add another larger border to finish it off in black. I do like the idea of a leafy green, maybe a hunter green, if you choose a solid color from the quilt I feel it may distract from your pretty florals. Only my opinion. Let us see what you decide when its completed. Its very pretty so far.

Beautiful Quilt!

I like the idea of a piano keyboard using black, a pretty leafy green and alternating with as many "keys" that you can from leftovers from the top.

Example: black/green/black/scrap/black/green/black/scrap/black

You could do small squares with black sashing, use your scraps from the quilt, and do like those film squares. God bless.

But there might be some scraps? How about a piano key border? And if there's not enough scraps you can add in some solid colours... pink, purple, yellow...

I guess I'm a little different. I would do say 2 thinner green borders about 1 1/2-2" each and a wider floral that picks up the colors in the top between them and then bind in black.

The quilt is beautiful. Make the quilt the star, don't make the borders anything that will take away from it. Dark borders would be my preference. How about Dark borders with a pieced binding of scraps left over from the blocks?

what about a lovely pale blue batik that looks like water. you don't have blue in there so you could call it a water garden. This way you wont have any colors fighting for dominance in the quilt.

It appears you only have a small bit of yellow when looking at the overall quilt and it does not overshawdow the other colors. perhaps a small print of a pale yellow narrow border that will frame it and finish off with a wider Black frame.
The quilt is beautiful and have been told yellow can act as a neutral if not overpowering.
It will certainly contrast the black and the quilt colors. Make the border the same or a little smaller than the current black outside border.
I love the black...one of my fav colors in a quilt.

what are you doing for backing? I would use a tone from that.

I didn't think about the backing yet, my border will have to be at least 7.5-8". I have to make it big enough to go the top of side rail. Keep the suggestions comming. Thanks, it always helps to get others views.