Gail asked about how I sew buttonholes on narrow knit bands, so I thought I should share the methods that I use when working with knits. I'm sure there are more ways out there so please chime in in the comment section if you have other tips!
One way stretch interfacing method
This method works very well on jersey, interlock and rib knits. The tricot interfacing I use for this purpose only has one way stretch and I place the interfacing so that it stretches crosswise and subsequently takes away the lengthwise stretch of the fabric, which is good since I will sew vertical buttonholes.
1. First interface the placket. If the fabric is relatively firm I only use interfacing on one side, but for stretchy fabrics it's good to have interfacing on both sides of the button placket.
2. After you stitched the placket just sew regular vertical buttonholes, just like you would have done with woven fabric.
3. There you go! The upside of this interfacing method is that it keeps the buttonholes from stretching out. The slight downside is that it makes the placket a little stiff, but it's a minor thing in my opinion.
Using elastic thread
This method is great for fabrics that you can't or don't want to interface (such as ribbing). You can also use this method in combination with 4-way stretch interfacing.
1. What you do is stitching over a thin elastic thread which keeps the buttonhole from losing its shape when stretched out. My Bernina buttonhole presser foot has a special slot for the elastic, so it's easy to sew on the elastic thread. I assume other brands has similar solutions.
2. Afterwards it looks like this
3. Then you just drag the elastic to remove the loop
4. Using a needle, move the elastic to the back side and attach them either by making a knot or sewing them to the fabric.
When all else fails
I am not good at making buttonholes in delicate knits or spongy knits, though Connie Long has great pointers on that in her book. Instead I resort to my favorite "cheat" which is using a combination of metal snaps and buttons. Like this:
Yes, it's not the same thing as proper buttonholes, but I really like this style as it reminds me of vintage garments.