Chain 25, 4th Chain from Hook, DC 3 times into the same stitch, *Skip 2 chains, DC 3 times into next. Repeat * to the 3rd chain before the end. Slip Stitch to the 1st chain to create a loop at the end. Middle section of your afghan is now ready to begin doing the regular granny square concept.
Chain 3, 2 DC into the ch-2 gap (partial 1st corner made), Ch 1, (3 DC, Ch 2, 3 DC) into the same ch-2 gap (1st side and 2nd corner made). *Ch 1, 3 DC into the next gap. Repeat from * all the way to the end ch-2 gap (2nd side). In the end gap, 3 DC, CH 2, 3 DC, Ch 1, 3 DC, 2 CH, 3 DC (3rd side and 3rd & 4th corners made). *Ch 1, 3 DC into next gap. Repeat from * along the same side (4th side). My transitions to the next row ended up differently. I would finish the 3DC in the ch-1 sp before the corner, ch-1, slip stitch to next 3DC in corner, ch-1, skip 2 stitches and slip stitch, ch 3, 2DC, ch 2, 3DC and keep going (the way I work mandala rounds.)
When you get to the last corner, (partial 1st corner), finish the corner with 3 DC, CH 2, and then slip stitch to the top of the chain 3.
With each round, the middle sections between the corners get wider. In any Ch-1 Gap Space between the corners, we will always put in 3 DC followed by a Ch 1. Follow the same concepts in step 2 for beginning your round and handling your corners.
Finish your afghan when you get to the size that you desire.
Edging: With edging color, slip stitch into corner ch-2 space, *ch 4, attach to next ch-1 space with slip st.* Repeat **. Treat corners like ch-1 spaces.
adapted from Crochet Crowd