I also use the plastic mini-blind slats and mark them with pencil. I like mechanical pencils because they are always sharp. I have pencils for 0.7 mm wide lead, and a few for 0.9 mm wide lead. I see that there are even some 1.3 mm mechanical pencils made!
http://www.amazon.com/s?rh=n:1...
When I use them in insert rays or propagation trays with small cells, I cut them in half lengthwise. I like the way the curved slats lay flat against the walls of circular cells.
When labeling a 128-cell tray (8x16 cells, with "ribs" in the small square cells), I cut the slats into thirds so they fit more neatly into the cells.
I also plan the heights of the mini-slat labels to be uniform, about 2" taller than the depth of the cells. That way, I can drape Saran Wrap over the tray instead of a clear humidity dome. That way I can uncover half the tray while keeping the other half at 100% humidity.
I have a roll of 18" Saran Wrap that I hope lasts the rest of my gardening career!
