Thanks, Linda! Al (Tapla) gave me the idea, and yes, it is for pulling that perched water out of the bottom inch or so, giving the roots an extra inch or more.
But Al keeps reminding me that mats and wicks for pots are NOT as good as really really well-draining mix (and watering often).
So I keep trying to improve my potting mix by removing fines. In small cells only 1" or so accross (like a 72-cell tray) you can't use VERY big bark chunks! They don't fit well.
And seeds that need to sprout on the surface like petunias can't afford to fall into deep gaps between coarse chunks. I learned that last spring.
Off topic, I keep sabotaging sprouts by leaving them in shallow cells or cups too long, or even in 3" pots longer than their roots like. Partly I'm afraid to put them outside where slugs tend to mow them down, partly I never seem to have time when I need it, and partly laziness is always a factor.
Why don't soil mix recipies include a bushel of discipline as the most important ingredient?
