3.
Like sewNsow, I water seedling trays with a sprayer mist when I can't resist watering them. It keeps the surface moist without necessarily adding huge amounts of water. And sometimes I'll just spray the inner surface of the humidity dome.
A sprayer is also good when you have a overpowering yen to water seedlings that have emerged but don't yet have many roots. Less is better!
I agree with sewNsow that a turkey baster is good for watering ... IF your hand is steady.
But if you're like me and somewhat spazzy, consider saving a ketchup bottle. The small hole lets out an even finer stream of water than a turkey baster does, and lets you aim them.
I often water onto the plastic dividers and corners between cells - that way, no water splashes onto soil, it just splashes onto plastic BETWEEN cells and runs off gently onto the outer periphery of each cell.
A shakey hand is almost a benefit, since it shakes mere droplets out of the ketsup bottle.
But a turkey baster is an absolute necessity for an over-waterer, because you can pull standing water out of the trays when you over-water, either from the top or from the bottom.
I don't know any other way to prevent fertilizer salts and soil acids from building up in the tray as water drains out of cells and pots and then evaporates from the tray, leaving salty acid behind. The acid soon eats the cotton flannel to shreds!
Maybe the trick should be potting up out of the small inserts **ASAP**, instead of waiting for the roots to get extensive enough that they hold the soil ball together when I plant out. I prefer that for planting out, because you can "pop and drop" whole root balls into planting holes without the root ball tearing itself to shreds.
If seedlings never stay in trays long enough to develop root balls, they might never accumulate salts. But if I hope the plants will survive my clumsy handling, I have to pot them up while sitting down right close to the trays and pots in good light, not trying to bend over to reach ground level while the baby roots fall apart in my hand. Emphasize "trying to bend over" (With my legs, squatting isn't an option.)
(The following is mostly for very clumsy people, or if you can't squat or bend very well. Another metohd is to build tall raised beds with deep walkways (trenches) between them. Then the soil is at knee or waist level even before you try to bend.)
My best planting-out technique is to pop a solid root ball (root bound, unfortunately) out of a cell or pot and onto the tip of a "sharpshooter" or trenching spade. Then I can lower the root ball and let it slide gently into the planting hole even if the hole is in the middle of a 5 foot wide bed.
