Long curtains look messy as they pool on the floor, and they may not slide open and close smoothly. Shortening the curtains without cutting them down and adding a permanent hem allows you to reuse them on a larger window later, since you only need to let out the temporary hem. No-sew hemming options are also suitable if you don't have the time or skills necessary to add one properly.
Shorten the Top
Pocket-rod curtains have a pocket in the top that the curtain rod slides into. These are some of the easiest curtains to install because they don't require hooks. You can shorten these without a permanent hem by folding the top over toward the back of the curtain. Pin the fold down to create a new pocket to slide the rod into. If you pin only into the lining of the curtain, the pins won't show on the front of the curtain.
Shorten the Bottom
Nearly any curtain design still looks good if you shorten it from the bottom instead of the top. Avoid cutting by folding up the bottom to the desired curtain length and pressing it with a hot iron to create a crisp edge. Pin the fold in place with safety pins through the excess material and into the curtain liner, similar as you would with the top of a pocket-rod curtain.
Sewing a basting stitch along the folded section of the curtain provides a temporary hem and a cleaner look than pinning. Basted hems are attractive on both the front and back of the curtain. Sew a long running stitch to secure the folded material in place. Remove it by snipping off the knot and pulling out the thread. Adhesive hem tapes provide another alternative. Apply these by removing the adhesive paper on one side of the tape and sticking it to the curtain. Fold up the overly long curtain portion, remove the paper from the front of the hem tape, then stick the curtain in place to secure the fold. Some hem tapes leave behind a residue that may stain the fabric, so it's best to test it on a hidden area of the fabric first.
You can move the curtain rod and give the appearance of shorter curtains and a larger window at the same time. If your curtains are 4 inches too long, raise the curtain rod 4 inches. This does require drilling new holes for the rod mounting hardware. The old hardware holes also require patching and repainting, so this option is best for a long-term solution on a window that's not sized for standard curtains.