That would depend on the size of the particular seed and the methods used for germination.

Personally I germinate 25-30 tomato and pepper seeds, as an example, in 2X2" cell while some new to the process put only 1 seed in the same size or larger cell. Herbs and perennials are often germinated in clusters of several seeds rather than spaced individually.

a rule of thumb for how deep seeds should go, which is either 2 or 3 times their diameter, depending on who you believe!

Depending on who you believe - exactly! Personally I would never advocate that as a "rule", merely as a very general guideline at best. While it is more applicable when direct seeding in the garden it has much less of a role when germinating seeds indoors.

The problem with trying to provide "rules of thumb" is that they seldom apply to many different situations.

Dave

Averages are just that -- averages. When I winter-sow in milk jugs I just throw the seeds in and water. Then they are sealed and put outdoors to freeze/thaw/be covered with snow. I just figure that when seeds self sow, they usually are not covered except by falling leaves and animals digging them in.

My success with winter sowing is excellent. They just plain don't need to be covered since they don't need protection from birds or other varmints. But - when I start plants indoors I cover with a bit of soil just to keep the seeds from drying out before germination.

I plant seeds outside in 18 cell flats; bring flats into garage when I expect a freeze. I may plant up to 4 cycles a year.
I use a personal rule that works for me:
Soak most seeds (except ultra tiny) before planting. Plant in loose soil so roots can penetrate.
Barely cover and keep reasonably moist till germination.

Spacing? Plant far enough apart that I can lift them out of the cell with minimal disruption.
Right or wrong, it works for most of my seeds.
Certainly don't expect anyone else to follow what I do.

This post was edited by bugbite on Sun, Mar 3, 13 at 9:52