I use painters tape and a small piece of paper. I write what it is, grams of seed and the date planted. Also, growing medium if I’m doing a side by side comparison. When I harvest the tray, I write the yield on the paper part of the label and any changes in seeding rate, if needed. When I first started growing, I kept all of the tags for review and decision making. Now, I keep the tags only if I’m trying to get the seed rate dialed in.