This spring I faced the challenge of planting up a large quantity of patchoy seed ... fits the 'small as a grain of mustard seed' analogy.
When you are planting trays which consist of 100 cells per tray hence the dilemma.
Big fingers, little seeds, many cells ...
So I hit upon a little technique using a bamboo skewers ... still takes patience ... but works quite well. Not even necessary to dampen and flick the skewer with each new seed.
I made a little Youtube video of the process:
(Copy and paste the link to your browser.)
See if you find it useful.