How to Add a Snowball Corner to a Half-Square Triangle (HST) Block

One of the simplest ways to elevate a quilt block is with a snowball corner. This small touch can transform the look of a block, add movement, and create secondary patterns when blocks are joined together. Today, I’ll walk you through how to add a snowball corner to a half-square triangle (HST) block.

What is a Snowball Corner?

A snowball corner is when you stitch a smaller square onto the corner of a larger block, trim away the excess, and press it open to create a new angle. It’s often used in the classic Snowball block, but it works beautifully on HSTs too.

Snowball corner added to an HST block

Materials You’ll Need

  • HST block (any size)
  • Small squares of fabric (for the snowball corners)
  • Fabric marker or pencil
  • Ruler
  • Rotary cutter and mat
  • Sewing machine and thread

Step 1: Choose Your Size

Decide how large you want your snowball corner to be. A common choice is a square that’s ¼ to ⅓ the size of your HST block.

  • Example: For a 6″ finished HST, use 2″ squares for snowball corners.

Step 2: Mark the Stitch Line

On the back of your small square, draw a diagonal line from corner to corner. This will be your stitching guide.

Step 3: Place the Square

Position the marked square on one corner of your HST block, right sides together. Make sure it aligns perfectly with the edges.

Step 4: Stitch

Sew a scant seam just to the right of the drawn line. This helps the corner lay flatter once pressed open.

Step 5: Trim and Press

Cut away the excess corner, leaving a ¼″ seam allowance. Press the triangle open toward the corner fabric.

Step 6: Repeat

You can add one snowball corner or place them on multiple corners of your HST for different design effects. Try experimenting with two opposite corners or even all four.

Design Ideas

  • Single Corner: Adds a subtle accent.
  • Two Opposite Corners: Creates a diamond effect.
  • Four Corners: Transforms the HST into a completely new block.

Adding snowball corners to HST blocks is a fun way to customize your quilts and play with secondary patterns. Try mixing solids with prints for extra contrast, or keep it monochromatic for a more subtle look.

Below is a recent commission quilt I made using snowball corners.

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