You just need to remove the cap from the milk jug, and that will be enough ventiliation, IME.

I usually sow my tomatoes a bit more thinly than other things, but that is because I don't grow as many (i.e. 15 tomato plants vs. 150 zinnia plants, lol). And I keep my tomatoes separated by variety.

So, I may plant 4 to 6 tomato seeds of one variety in one jug, then another 4 to 6 of another variety in another jug, etc. But that is just for my ease of planting later, and again because I don't grow that many. (I plant at least 4 seeds for each variety to assure germination of at least one seed).

I assume you can put as many seeds as you'd like in a jug - I've seen tomatoes self seed in very large numbers in one little spot, like where a tomato may have fallen and been left in the garden, and all those seeds in that little 2-3 square-inch area germinate!

:)
Dee

Dee, thanks for the very informative post. Just what I wanted to know.
I definitely plan on putting different varieties in different jugs and marking them well.
Take care,
Steve

I don't winter sow tomatoes because in Z5, they don't have a long enough growing season. Those and peppers are the only things I start indoors. Everything else will be WS in milk jugs.