Now as things are poking out of the ground and showing you their darling little first leaves, make your first selections. What I mean is, select OUT of the population the ones you don't want. To save seed, you want to save from good plants- not the crappy ones left over at the end of the season that went to seed after you neglected them. If you are thinning your population anyways for proper spacing, thin out the ones that germinated late, look a little off-type, or that are small compared to the rest. If the part of the plant you thin is edible, toss it in your next salad.
This is what good seed-savers do. They select out the plants they don't want flowering and reproducing. The great thing is you get to decide what your own selection criteria is. If you want variation in size, color, or whatever, then make that decision and go for it. You are in charge!
I'll give you an example of a selection I made last year. I planted some 5th generation home-saved kale seed from a local college professor. He called it purple kale. It turns out there was a bit of variation in color and leaf texture so I could decide what I wanted and push the population in that direction. There were both green and purple kales- some really crinkly, some way less so. I decided I only wanted green kale, and especially the flatter-leaved kind because it just so happened the flatter leaves were sweeter. So I selected all the purple out, and as much of the frilly leaves out as I could. I couldn't remove all the frilly leaved kale because I would have made my population too small to be meaningful. Now I have to plant the seeds and make more selections.
|Me with some of my flatter leaved kale|