Seed stitch is a simple knitting pattern using only two stitches -- knit and purl. To create the seed stitch, you knit a stitch, then purl a stitch, continuing the alteration for an entire row of knitting. When you turn your work to begin the second row, you knit the purl stitches and purl the knit stitches.
Moss stitch is a variation of the seed stitch. Start as you would to create the seed stitch, by alternating one knit and one purl stitch across a row. When you turn your work to begin the second row, knit the knit stitches and purl the purl stitches. For the third row, knit the purl stitches and purl the knit stitches. The rest of the rows continue by alternating as you did for rows two and three.
The double moss stitch creates a more loosely structured piece of knitting. Begin as with the basic seed stitch, except double the stitches -- two knit stitches, then two purl stitches, alternated across the first row. When you turn your work, knit the knit stitches and purl the purl stitches for both rows two and three. On rows four and five, knit the purl stitches and purl the knit stitches. Repeat this same pattern by alternating your stitches as you did for rows two through five.
You can create some interesting variations on the seed stitch by alternating two different colors of yarns or by using a yarn that varies in thickness, suggests Kara Gott Warner, editor of Creative Knitting magazine. You can also alternate the sizes of your knitting needles to create an undulating effect.