How to Join Granny Squares: Six Methods, Three You'll Actually Use

There are six standard ways to join granny squares. The reason every tutorial enumerates all six is that the methods produce different-looking finished fabric, not because all six are practical choices for any given blanket. In practice, most crocheters settle on two or three favorites and stop thinking about the other ones.

The decision tree is short: do you want the seams to disappear (mattress stitch or whip stitch), be part of the design (single crochet, double crochet, slip stitch), or not exist as separate seams at all (join-as-you-go)? That's the whole question. The rest is technique.

This guide covers all six methods so you know what they look like, then says which one to actually pick for the project you have in mind.

Before you start joining

Three pre-join steps that change how the finished blanket looks.

Weave in ends per square. A blanket of 80 squares has 80 to 160 yarn tails. Weaving them after joining means working around the seams to access the wrong side of each square, which is slow. Weaving per square as you finish them spreads the work out and is faster overall.

Block each square. Granny squares come off the hook slightly distorted; the corners are wonky and the size varies by a quarter inch from square to square. A light wet-block (soak, press out water, pin to a uniform size, dry flat) makes them all the same dimensions, which makes joining cleaner. Skipping this step is fine for a casual blanket where slight variation reads as handmade charm; do it for anything you want to look more polished.

Lay out the squares before joining. All of them, on the floor, in the arrangement you want. Photograph the layout. The photograph is your reference while joining; otherwise you'll forget which order they go in by the third row.

The six methods, ranked by visibility

Mattress stitch (invisible, slow)

A sewing method. Threading a tapestry needle with matching yarn, then weaving back and forth between the edge stitches of two adjacent squares so the seam pulls them together. Done correctly, the seam disappears completely; the two squares look like one continuous piece of fabric.

The catch is speed. Mattress stitch is the slowest method by a noticeable margin. A 6x6 granny-square blanket (36 squares) takes about three to five hours of mattress-stitch joining for a competent sewer. The same blanket joins with single crochet in under an hour.

Use when: you want the blanket to read as one continuous piece. Wedding gifts. Heirloom afghans. Any time the squares are very different colors and you don't want a contrasting seam line.

Whip stitch (mostly invisible, faster)

Another sewing method. The needle goes straight through the edge stitches of both squares at once, looping over the top of the seam. Faster than mattress stitch because you're not alternating between two squares, just passing through both.

The seam is slightly more visible than mattress stitch but only at close inspection. From any normal viewing distance, it reads as invisible. Tension control is harder; if you pull too tight, the seam puckers, and if too loose, the squares gap.

Use when: you want near-invisible seams but the project is too big for mattress stitch's time budget.

Single crochet (visible, fast)

A crochet method. With both squares held wrong-sides-together (or right-sides-together for a different look), you single-crochet along the edge through both squares' edge stitches. Each stitch joins one stitch from each square.

The seam is visibly a ridge of single crochet. On the public side, this reads as an intentional design element: a contrasting-color seam looks like a deliberate stripe between squares. Many traditional granny-square blankets use single crochet specifically for this look.

Use when: you want the seams to be part of the design, especially with contrast-color joining yarn. Modern aesthetic, faster than sewing, the visible seams read as intentional.

Double crochet (very visible, very fast)

Same technique as single crochet joining but with a taller stitch. The seam ridge is twice as tall and forms a more prominent grid pattern across the blanket. Most useful with chunky or bulky yarn where the scale matches; in lighter yarn it tends to look heavy.

Use when: you want a bold grid effect, often with bulky yarn or with contrast color joining.

Slip stitch (visible, very fast)

The fastest sewing-or-crochet method. Both squares held together, slip-stitch through both edges. The result is a tight, somewhat stiff seam that holds the squares firmly but reads as a clear line on the public side.

The downside is rigidity: a blanket joined entirely with slip stitch is less drapey than one joined with sewing methods or single crochet. For a wall hanging or a structural piece this is fine; for a snuggle blanket it can feel cardboard-y.

Use when: speed matters more than drape. Practice swatches. Charity blankets. Anything you need to finish quickly.

Join-as-you-go (no separate joining step)

A construction method, not a finishing method. You crochet each new square attached to the already-joined squares during the final round of the new square. By the time the last square is done, the blanket is also done; no separate joining phase.

The technique requires reading the pattern attentively because you're tracking position relative to neighbor squares during the final-round chains. Some join-as-you-go patterns are designed for it explicitly (the final round has built-in join points); others adapt any granny-square pattern to it by substituting single-stitch joins for chain-spaces during the final round.

Use when: you don't want a separate finishing phase, you're motivated, and you're working a pattern that supports it. The blanket is "done" when the last square is finished; no basket of squares waiting to be assembled.

Which method to pick

Three practical recommendations:

Default to whip stitch for traditional-looking, near-invisible seams on most blanket projects. It's the speed/invisibility sweet spot. Most modern granny-square blankets are whip-stitched.

Pick single crochet with contrast yarn for a modern look. The visible seams become the design feature. This is the technique behind most Pinterest-aesthetic granny-square blankets where the seams contribute to the pattern.

Pick join-as-you-go if you hate the assembly phase enough that you'd skip making a blanket to avoid it. It's not faster than single crochet overall, but it interleaves the joining into the making, which feels less daunting psychologically.

The other three methods (mattress stitch, double crochet, slip stitch) are for specific cases: heirloom invisibility, bold grid aesthetic, and speed-over-everything respectively. Don't pick them for general use.

Three projects to practice the joining decision

Classic Granny Square (the first one)

Classic Granny Square

Find this pattern on HoneyBee

Purl Soho. Worsted weight, H/8 hook. The standard granny-square anatomy in clean instructions with a step-by-step photo tutorial. Make twelve of these (three colors, four squares each), then join four of them with mattress stitch, four with whip stitch, and four with single crochet. The 12-square sampler is the fastest way to see what each join method looks like on a finished piece. Once you've seen the three side by side, you'll have a strong preference and won't second-guess the choice on bigger projects.

Granny Square Baby Blanket (the sewing-method blanket)

Granny Square Baby Blanket

Find this pattern on HoneyBee

Lauren Brown. Aran weight, I/9 hook. Striped-color granny-square baby blanket, beginner-friendly construction. The pattern doesn't specify a join method, so you choose. For a baby blanket, whip-stitch is the right call: invisible from any reasonable distance, fast enough to finish in an evening, and the relatively small total size (typically 36 squares for a baby blanket) means you're not spending three days on the join phase. If the recipient is sensory-sensitive, whip-stitch from the wrong side so there's no seam ridge against skin.

Sunny Spread (the join-as-you-go blanket)

Sunny Spread

Find this pattern on HoneyBee

Ellen Gormley. Aran weight, J/10 hook. Granny-square afghan designed explicitly for join-as-you-go construction; the final round of each square has built-in attachment points to neighboring squares. The technique becomes intuitive after the first four squares: round 1 to 3 is a standard granny square, and round 4 attaches to whichever neighbors already exist. By square 30 you stop thinking about it. The pattern is the right learning vehicle for join-as-you-go because it was designed for the method, rather than retrofitted from a separate-square pattern.

Joining geometry that matters

A few details about how to actually align two squares for joining:

Right side together or wrong side together changes the look. Wrong-sides-together (the public sides face out, the joining happens on the inside) gives a flat seam visible from the inside but hidden from the outside. Right-sides-together (public sides face each other, joining happens on the outside) gives a seam that lies on top of the public side; that's the design choice for visible-seam methods like single crochet with contrast.

Corner stitches need extra attention. Granny-square corners have three or more clustered stitches and the joining method has to handle them. For sewing methods, two stitches in the corner (one for each side's corner cluster) is standard. For crochet-joining methods, the corner can be a chain-space or an extra stitch depending on what makes the seam lie flat.

Always join in the same direction. If you join row 1's seams left-to-right, do every row left-to-right. Inconsistent direction produces twist in the fabric that doesn't block out.

Block after joining. The seams settle after a light blocking and the whole blanket squares up. Even if you blocked each square individually, a final block of the assembled blanket evens out everything.

Common mistakes

Mixing yarn weights between squares and joining. If your squares are worsted and you join with DK, the seams will pucker. Match the joining yarn to the square yarn unless you're deliberately going for a contrast effect with a different texture.

Joining without blocking the squares first. Joining unblocked squares means working with wonky, slightly-different-sized pieces, and the result has visible irregularity at every seam. Block first.

Pulling the joining yarn too tight. All five sewing-and-crochet methods produce puckered fabric if the joining tension is too tight. The seam should be snug, not tight; the blanket should lie flat when you spread it out without pulling.

Not weaving in the joining tails. Each seam usually starts and ends with a yarn tail that has to be woven in. Treat them like any other yarn end: 2 inches in, half an inch back, trim flush. Skipping them is the most common reason joining tails come loose six months later.

Picking the wrong method for the project. A drapey, snuggleable adult afghan joined with slip stitch will feel like a stiff board. A wall hanging joined with mattress stitch will sag because mattress stitch is too forgiving. Match the method to what the blanket is for.

FAQ

Can I mix joining methods in the same blanket?

You can, but it usually looks accidental rather than intentional unless you make the method choice obviously deliberate (different-colored joining yarn for the central rows, or a contrasting border join). Most consistent-looking blankets use one method throughout.

Which method is best for join-as-you-go beginners?

Single-crochet join-as-you-go. The mechanics are intuitive (catch the neighbor's edge stitch with a single crochet during your final round) and the join is visible enough to confirm you're doing it right. Slip-stitch join-as-you-go is faster but harder to learn because the joins are nearly invisible from the front and beginners can't tell whether they actually joined or just slip-stitched into their own square.

What if my squares are slightly different sizes after blocking?

Whip stitch is the most forgiving. You can ease the smaller square into the bigger one over the length of the seam by adjusting tension. Mattress stitch is less forgiving; it expects equal-length edges. Crochet-joining methods are intolerant of size mismatch.

Should I use the same yarn for joining as for the squares?

Default to the same yarn, in the dominant color of the project or in the color of the bordering squares. Using a different yarn means the seam shows differently when held against the squares, which is usually unwanted. The exception is deliberate-contrast joining for visible-seam methods.

How much extra yarn do I need for joining?

Roughly one ounce of yarn per dozen squares for sewing methods; somewhat more for crochet-joining methods. For join-as-you-go, the joining yarn is built into the per-square yardage so the only extra is what you'd use anyway.

Related guides

• Granny Square Crochet for Beginners
• How to Weave in Ends
• How to Block Your Knitting and Crochet
• Free Granny Square Patterns
• How to Crochet for Beginners

For yarn-weight conventions (which determine whether your joining yarn will match the squares cleanly), the Craft Yarn Council's yarn weight system is the universal reference.

Whip stitch for most blankets. Single crochet with contrast yarn if you want the seams to count as design. Join-as-you-go if you hate finishing phases. The other three methods exist for specific cases.