Wow, that is a great idea! And I already have some because I use them to drop my glue on my seeds when making seed tape. And I'm pretty sure I have irrigation tubing too. I'm going to try that!
I like the mini-blind idea but then I have to do more dumpster diving or freecycling for the blinds first! Ha!
I'll have to try the mechanical pencil. I have used china marker but they don't stay sharp AND if you leave them out in the sun they melt and you can't peel the paper off any more. I use Mr. Clean Magic Eraser to erase the plastic labels where needed.
I bought the plastic labels for in the GH stage and for my plug trays, I used a paint pen and marked tray number on the side then number for each row because I planted as many as 12 different kinds of seeds in a tray. then I used a tablet and labeled tray number and corresponding rows and wrote down each type of seed and how many planted. Then when they germinated I added that info and eventually how many total germinated.
Really though, I've been doing seeds for a long time so I pretty much know which ones are fast and which ones are slow,, which ones need heat, which ones don't, etc., so I did try to plant accordingly. And I spaced out things that I had several varieties of, like my coleus (and I didn't wash the seeds out this year!)
The main thing is, I just love planting that seed and watching every day to see if anything has peeked through! Oh yeah, I also have a headband magnifier and a broken dental curette to prod with! I'm pretty extreme!