(If you don't give a rat's hiney about knitting, save yourself now and come back tomorrow for news about our pumpkin-picking adventurefest on Saturday.)
For anyone still here, please forgive the shoddy photography and scary alien hands. What can I say, I'm a first-timer and it turns out that this is harder than it looks. Anywho, here's how this works:
You can work a knitted hem at the beginning of a piece (for example, starting with the cuff of a sleeve, then turning and attaching it and working up from there) or at the end of a piece (for example, adding an edging to something then attaching the hem and casting off). Either way works like a charm.
For our purposes, let's start with a piece of stockinette. If you'll be asked to hem something, you'll knit in a turning ridge a certain number of rows in, which means you'll purl a knit row in a piece of stockinette, then go on your merry way. Once you have as many rows after your turning ridge as you do before it, it's time to knit yourself a hem.
Here's what your piece will look like (assuming you're using some leftover acrylic in a weirdly lit room):
Then fold your piece in half along the turning ridge and eyeball the line of stitches where the pieces will naturally meet:
Take a crochet hook, and coming from above the stitch, pick up a purl bump. The biggest trick here is to pick up the purl bumps in a line that's exactly straight. If you don't, you'll have a big, swear-word-inducing mess. Ask me how I know. Anyway, the stitch will turn when you pick it up, so before you put it onto the hook, eyeball the one next to it to make sure you know where you're headed next. I tend to run my index finger along the line of stitches as I go to make sure they're all lined up.
Using a standard-length crochet hook (one that's smaller than your knitting needle size by at least a bit), pick up a pile of stitches and leave them on the hook. I find that 15-17 stitches on the hook at one time seems to work best, but do what makes you comfortable.
Once you have a number of stitches picked up, you're ready to start knitting your hem. First, insert your working needle into the first stitch as if to knit and hold it there.
Now, you'll be using the back end of your crochet hook as a knitting needle. Use the working needle to pick up the first stitch on the crochet hook, as if to knit.
Wrap the yarn and knit the stitch...
... off of the crochet hook:
Now pull the newly worked stitch through the front stitch from the knitting needle.
You should have one loop on your right-hand needle now, and you're ready to work the next stitch in the same way.
NOTE: If you're working the end of a piece, you can cast off as usual once you have 2 loops on your right-hand needle, and proceed this way across the row.
I typically keep working across the row until I have 3 stitches left on the crochet hook, then pick up the next batch of purl bumps. This makes it easier (at least for me) to make sure I continue with the same line.
As you get to the last 8 or so stitches in your row, count to make sure you have the same number of stitches on the knitting needle and the crochet hook. If you've picked up stitches in a row, you should be relatively close. If you have one or two too many on the needle, just knit them without picking up a stitch from the crochet hook, and space them a few stitches apart. If you have too many on the hook, just drop one or two of them without knitting them (again spacing them a few stitches apart).
Once you get to the end of the row, you can either break the yarn and bind off or turn and keep going with your next row in pattern, working up from there. Here's how your super-professional knitted hem will look from the back side. Nice, no?
Easy peasy, too. So now you know. And I promise to use a better camera next time...