Sashiko stitching is done with a continuous running stitch sewn either by hand or machine in geometric and organic patterns that often have symbolic meanings. There are dozens of different patterns, but a few examples are: flax leaf (asanoha), symbolizing good health; bamboo (chiku), a symbol of prosperity; and the tortoise shell ("kikko"), symbolizing long life. One of my favorite patterns depicts cherry blossoms.
Traditionally, sashiko stitching was done in white thread on a dark fabric dyed with indigo, but it can be done in any contrasting color combination. Patterns are deceptively simple and motifs are repeated across the fabric. When doing the sashiko stitch by hand, it is important to learn how to sew the running stitches consistently so that each stitch is the same length with about 5-8 stitches per inch. A special long needle is used that has a large eye to accommodate the heavier thread used with sashiko. Numerous stitches are gathered on the needle before pulling the thread through the fabric. It is also important to not pull the thread too tight which can cause puckering, and when you change stitching directions: turning a corner, for example, leave a small loop of thread on the back.
Sashiko can also be done by machine though it will not have exactly the same running stitch effect as the hand method. Well, unless you happen to have one of Baby Lock's new machines that specifically does the sashiko stich. The video below shows what it does.
Click on the link if you would like to learn about machine sashiko (link opens a .pdf).
If you are interested in learning more about sashiko, there are a few tutorials online that you can view listed below.
Sashiko Tutorial at the Purl Bee. The Purl Bee also sells Sashiko Kits.
Sashiko Tutorial at Handmaiden
Sashiko Tutorials from Studio Aika. There are three tutorials that address the mechanics of sashiko and give tips on proper technique.
I need to make some pillows for my couch to liven it up and am thinking some bright teal with sashiko stitching would look wonderful. I also love this sashiko pillow done with several bright colors of thread.
There are several helpful books that discuss the sashiko technique in greater detail. I have recommended a few below that I particularly liked.