Sample Chart - garter st borders (bottom, left and right)
Do I have to add extra rows to a garter stitch border on a double knit afghan? If so how will I know when?
Normally the pattern will tell you exactly how many stitches to cast on. This should include the sts for the left and right borders as well. The bottom and the top borders shouldn't be any problem.
Unless, the pattern said to add your own garter st borders, then you have to add sts enough to make borders on each side. Then at the beginning you just knit all rows for your bottom border until reach desired length. Then knit all rows at the beginning and the end of rows (where you want your garter st borders to be). See sample chart above. Once you piece is done, then you can add the top border to it (not include in the chart).
If this confuses you, then please sent or link me a pattern, then we can work this out together.