Transfering Germinated Seed to Trays
There are many ways to end up with a single seedling per 1020 tray cell. Rather than sprinkling seed into each cell, and then thinning afterwards, my preference is to germinate in an easily sealed, warmed and isolated cup, then transfer the germinated seed to the cells.
Tobacco seed (which starts off at about 1/2 mm in size--500 microns), when exposed to germination conditions (warmth, moisture) will first swell, then elongate. This is visible to the naked eye. More dramatic is the moment its root radicle ruptures the seed casing and emerges. Since the radicle is bright white, it stands out like (in BigBonner's words) a Christmas light. This makes the germinated seed easy to spot, and easy to transfer singly to a cell.
Within a few hours of radicle emergence, green cotyledons may appear.
I wait until enough sproutlings of a particular variety have emerged to set up all the cells for that variety, then do the transfer. For small growouts (for seed refresh or for curiosity), I start 8 cells, and transplant 4 to the field. For larger grows, I provide 4 to 8 extras per variety.
I begin by adding a quart of water to the bottom of the tray. (Remember that I use a nesting of trays: web; solid 1020; drained 1020; cell inserts.) After making a divot in the center--with my fingertip--I then mist the upper surface of each of the cells that will immediately be started for a particular variety.
The little depression makes it much easier to transfer the sprout, and also maintains a more moist environment surrounding the sprout.
Transferring the sprouted seed can be done with a toothpick. I prefer using one blade of a forceps.
After all the sprouted seeds for a single variety have been placed, I then lightly mist each of those cells once more, to settle the wee sproutlet. Each separatable pack of cells (4 per pack in my case) gets its own Popsicle stick label with the variety name. I never mix varieties within a pack.
Because the transferred sprouts are still quite vulnerable to drying out, I keep them covered with a clear dome for the next few days or so. When I run out of domes, a cover of plastic wrap works as well--it's just something of a nuisance to handle.
So far, I have completed this process for about half of this season's grow.
Bob