For me, there are times where I can get away with sewing a knit top without a dart if the fabric is stretchy enough. However, not all fabrics are stretchy enough. This week I made a simple grey T-shirt and the fabric, although a knit, required that I use darts for shaping. I thought I would share my method of sewing darts in knits.
The primary concern with sewing a dart in a knit is to sew the dart nice and straight without stretching the fabric as you sew the dart. My solution is to use Solvy Water Soluble Stabilizer.
First, snip mark the dart legs on the edge of the fabric with very small snips, preferably 1/8 inch or less:
Mark the dart point with chalk. I push a pin through from the pattern through to the fabric, gently lift the pattern from the fabric and then chalk mark the point:
I then fold the dart and encase it in a piece of Solvy Water Soluble stabilizer and pin the dart. (Addendum 4/25/17: if you want to save on stabilizer, you can also cut strips instead of encasing the dart. Just make sure the strips don't shift out of place.) Since the stabilizer is see through, you can see your dart. However, if you want a clearer line, you can chalk mark on top of the stabilizer:
Wet the darts or wash the finished garment to dissolve the stabilizer. I then steam press by hovering a steam iron above the dart and patting it down with my hand. While doing so, I put a piece of paper underneath the dart to prevent a ridge from forming on the right side while I steam press. Following is a photo of the wrong side of the dart with the stabilizer dissolved:
Darts aren't always necessary in knits but for the more generously endowed, they are often indispensable for a proper fit.