dave said:... I can't add anything to them. ...
I was hoping that after I described the vast extent of my ignorance, that others would jump in and supply the missing answers. I did NOT want to hear that everyone is in the same boat and "ya just gotta keep trying" is the best answer.
I assume that everyone who has gardened on a large scale for more than a few years has rules of thumb for their
region and their methods and goals
: "I start THESE in mid-March and THOSE in early May", or "6 weeks in a 72-cell except vigorous veggies only last 3 weeks, so I start them in 50-cells". Especially: "these are worth starting 4 small batches, every 2-3 weeks from A to B".
Mostly what I know is what NOT to do. I am proud of my expertise in ways to kill seedlings. I think it was over on DG where someone listened to a rant, then went and did the opposite of everything
I had done for my first few years, and had good success.
- don't drown the mix through overwatering. They rot & the roots rot.
- don't drown the roots with water-retaining peaty-mix. Seeds rot, roots rot, and the seedlings die from damping off.
- don't try to start tiny seeds that are "sow on surface, need light to germinate" on top of coarse, fast-draining potting mix. They fall into dark cracks and die there. Sprinkle enough fine mix or vermiculite on the surface to support the tiny seeds.
- don't start more seeds than you can hold under lights until ready to harden off.
- don't leave them in their germination cells too long. They get rootbound BRIEFLY and then go into shock or die.
- don't bottom water a tray of cells in a bathtub unless you know what you are doing. Or schedule the plumber to unclog your pipes before
you start the bottom-watering comedy routine. Or make a YouTube video of the process - I wish I had!
- if you sow only 1-2 seeds per cell, germination will be low and you'll have empty cells or have to back-fill them from other seedlings.
- if you sow many seeds per cell, germination will be high and you will have to kill most of them.
- if you harden off Delphinium seedlings, slugs will eat them right down to the soil surface. Let them grow larger indoors, then harden them off surrounded by a moat, copper flashing, electrified foil, mine fields, belts of slug bait and machine-gun towers. Then one out of five seedlings may survive.