The most important crochet technique of all is fastening off, sometimes called tying off, or drawing the tail end of the yarn through the last stitch of your work to fasten it in place. If you don’t remember to tie off, or if you leave too short a tail on the yarn, all your hard work will be for naught as you watch the stitches unravel before your eyes.
You really don’t need anything for tying off other than a crochet hook and scissors. However, if you don’t enjoy weaving loose yarn into your work with the crochet hook, you can use a yarn needle instead.
Yarn needles look just like a giant embroidery needle and may be made of plastic or metal; the eye is large enough to accommodate worsted-weight or heavier yarn.
How to Tie Off
Since, when you're crocheting, you usually have just one stitch on the hook at a time, tying off is as simple as snipping the working end of the yarn, leaving a 6-inch or longer tail. Use your crochet hook to pull that tail through the loop of yarn currently on the hook, sliding said loop off the hook. Pull on the loose end to tighten that loop around the yarn tail, which secures the final stitch.
Weaving in Loose Ends
Now that you’ve tied off the last stitch, you must weave the loose tail of yarn into the crocheted fabric. You can’t just snip it off right next to the knot; eventually, the knot will unravel, and the stitches will begin to come apart.
Use the crochet hook to weave the yarn in and out of the crocheted fabric, mimicking the stitch pattern so the extra yarn isn’t obvious. Alternatively, you can pull the yarn tail through the stitches along one edge of the work.
Finally, if using the hook feels awkward, thread the yarn tail through a yarn needle. Use the needle to weave the yarn in and out through the fabric several times, switching directions for a more secure weave-in; then snip the remaining yarn tail close to the fabric.
When Not to Tie Off
As a general rule, you never tie off as a means of switching color in crochet. It will leave a small, but noticeable knot in your work that’s really unnecessary, as well as obligating you to re-attach another piece of yarn to begin stitching again, further disrupting your pattern. Instead, just switch colors in the very last part of the previous stitch; then carry the tail of the previous color along with you until it runs out. It will be neatly contained in your work, leaving no loose end that you’d have to come back and weave in.