How to Join Granny Squares: 5 Seaming Methods Compared

The join you pick changes more than how sturdy your seams are, it changes the whole look of the finished piece. Two blankets made from identical squares can look completely different depending on whether the joins sit as a visible decorative ridge on top or disappear into the fabric entirely. None of these methods are hard once you’ve done one seam, but picking the wrong one for your project is an easy way to end up redoing a blanket’s worth of seaming.

Whichever method you land on, a tapestry needle is the one tool every join on this list actually needs.

Whip Stitch: The Simplest Join

Whip stitch is usually the first join people learn because it only needs a yarn needle, no hook required. Lay two squares right sides together (or wrong sides together if you want the seam to show on the front as a decorative detail), thread your needle, and stitch through the outer loops of both pieces, working from one corner to the next, pulling the yarn snug after every stitch.

It’s fast and forgiving of slightly mismatched stitch counts, since you’re not trying to match stitch-for-stitch the way a crocheted join requires. The tradeoff is that it can look a little bulky if you go through both full loops instead of just the back loops, so for a flatter seam, catch only the back loop of each stitch on both pieces.

Slip Stitch and Single Crochet Seams

Both of these use a hook instead of a needle, and both leave a visible ridge on whichever side you work them from, that ridge is the point, not a flaw. Hold your two squares with the sides you want joined together, insert your hook through both layers, and either slip stitch or single crochet along the edge.

Slip stitch gives a flatter, tighter ridge. Single crochet gives a thicker, more pronounced one, and adds a bit more stretch to the seam, which matters if the piece is going to see any wear, like a bag strap or the edge of a garment. If you want the ridge visible on the front of the finished piece as a design element, work with the pieces held wrong-sides together; for the ridge to hide on the back, hold them right-sides together instead.

Mattress Stitch: The Nearly Invisible Option

This is the join to reach for when you don’t want any seam showing at all, it’s the same technique knitters use, adapted for crochet stitches. Lay both squares flat, right side up, edge to edge, not overlapping. Working with a yarn needle, pick up the horizontal bar between the first and second stitch on one square, then the matching bar on the other square, alternating back and forth like lacing a shoe.

Every few stitches, pull the working yarn snug to draw the two edges together, but don’t yank it tight in one go at the end, that tends to pucker the seam. If you use a yarn that closely matches your project color for the seaming, the join genuinely disappears into the fabric once it’s pulled up, which is why this is the go-to method for anything meant to look like one continuous piece rather than assembled squares.

Join-As-You-Go

This one skips the separate seaming step entirely by joining each square to its neighbors during the final round, instead of after. When you reach a corner or side that borders an already-finished square, you replace your usual chain stitch with a slip stitch (or single crochet) into the corresponding space on the neighboring square, then continue your round as written.

It takes a little more attention than seaming squares after the fact, since you have to track exactly where each join needs to happen mid-round, and it only works cleanly if your squares are the same size and round count. But it eliminates the entire final seaming stage on a big project, which on something the size of a full blanket saves a genuinely significant amount of time, and there are no loose square edges to keep organized while you work.

The Flat Join, for a No-Bulk Seam

If a raised ridge on either side isn’t what you want, but mattress stitch feels too fiddly, there’s a middle option: lay your squares side by side (not stacked), and work your join stitches through the inside loop of the edge stitches on each piece rather than through both full loops. This produces a seam that lies almost completely flat, with a faint cable-like line on the front and a subtle running stitch on the back, no bulky ridge on either side.

It takes slightly more care to line up than a standard whip stitch, since you’re working through a narrower loop on each square, but for garments, where a bulky seam under a sweater or bag strap gets uncomfortable fast, it’s worth the extra attention.

Picking the Right One for Your Project

• Want the seams to disappear: mattress stitch, matching yarn color.
• Want the seams as part of the design: slip stitch or single crochet, worked with pieces wrong-sides together so the ridge shows on the front, often in a contrast color.
• Making something large, like a blanket: join-as-you-go, it saves you from seaming dozens of squares separately at the end.
• Making a garment or bag, where bulk matters: the flat join, or mattress stitch if you don’t need it fully flat.

Before You Seam Anything

Block every square first. It sounds like an extra step you can skip, but an unblocked square with slightly curled or uneven edges makes every join harder, no matter which method you’re using, since you’re fighting the fabric instead of just following the stitches. A few minutes of steam blocking per square saves real time once you’re seaming ten or twenty of them together.