Today my new flat of Bloomsdale Long Standing spinach under the kitchen grow lights sprouted! I also decided to start over with the original flat of Melody Hybrid. I "harvested" the leaves last week thinking that pinching them all back hard would encourage growth, but I think these plants are spent -- there's been no new growth in days and the remaining stumpy, leafless stems look pale and weak.
I did make use of the leaves -- I enjoyed a couple of sandwiches with fresh spinach and made a pita pizza with spinach and feta. This time around I'm going to see what I can do to make sure the new flat of spinach yields more. I'm adding a second flat with drainage holes to the original flat without holes and mulch with the very fine sphagnum peat moss, instead of the less-fine variety I had been using a few months back. I'm also going to water more regularly with compost tea. Still going to use Melody Hybrid in this particular flat. It'll be interesting to compare the growth of two indoor spinach flats, each with a different variety of spinach.