The most common method of closing this gap is to pickup an extra stitch in the gap itself. This works pretty well, but sometimes the pickup forms a small hole just below the pickup and then we are back where we started, having a hole that needs to be closed during finishing.
Not satisfied with the typical method, I decided to take advantage of the two stages of picking up and knitting gusset stitches. When I pickup stitches along the gusset, I pickup the stitch and then knit it through the back loop. I take advantage of these two steps to close the gap by picking up 2 stitches and then knitting them together TBL.
So here's how its done:
First, pickup the required number of stitches up to but not including the gap pickup, then pickup 1 stitch on each side of the gap, between the heel flap and the instep (just do the pickups, do not knit them yet). Once you have the two pickups on the needle, knit the 2 pickups together through the back loop to close the gap.
Lets examine this in detail:
|Identify the location of the 2 pickups. On the instep side choose the stitch 1 below the first stitch on the needle.|
|Put the needle through the first location (heel flap side)...|
|... and pickup the first stitch|
|Put your needle in the first stitch below the first stitch on the left needle ...|
|... and pickup the second stitch, on the instep side. There are now 2 pickups on the working needle. Neither pickup stitch has been knitted.|
|Put the left needle through the 2 stitches, in front of the working needle. The 2 stitches will be knit together through the back loop.|
|The two pickups have been knit together through the back loop.|
When you get to the other gusset, the instep stitch will be picked up first, followed by the heel flap pickup. The rest of the process is the same.
The gusset corners will look like:
|Heel Flap to Instep Gusset||Instep to Heel Flap Gusset|
|1st Stitch Below Pickup|
Here are some variations that may be of use depending on your sock pattern: