*[1sc, skip two stitches, 5dc], repeat from * to end.
Tip: When working a project in the flat, such as an crochet afghan, set your pattern up with an even number of your pattern (ie: if doing a shell afghan, do an even number of shells across), and an even number of rows, ending your last row on the right side of your project.
This pattern does not have to be followed exactly. It can be adjusted to work with, and fit your project. You can add one or two extra double crochets to the shell and skip an extra stitch or two between the single crochet and shell if you need to make this border work with your project. I align my border with the pattern of my project. If you want a little more ruffled texture in your border, consider adding an extra double crochet or two to your shell. Have fun and play with it.