I start some of my seedlings in pop bottle greenhouses. Tomatoes and green peppers are the first. I'm a little late getting started this year. Last year I had tomatoes started by January 25th. I planted more tomatoes every couple of weeks until mid March. They all ended up producing at pretty much the same time, so I don't think it makes too much of a difference. Some of the earlier plants may have been a little bigger, but mostly I had to wait for the weather to cooperate and then they all took off with a growth spurt.
To make a pop bottle greenhouse, you need to save empty pop bottles. Wash them out and remove the labels. Then, about an inch above the bottom rim, poke through the bottle with a serated knife.
I use scissors after I have the hole started, and cut all the way around the bottle.
Next, cut four evenly spaced slits up from the bottom of the top section, about 2 inches long.
Fill with your dirt/potting soil/starting medium of choice. I use dirt/compost. We fill 4 or 5, 5 gallon pails with dirt from a well aged manure pile in the fall, and keep them in the garden shed until spring. I add some water, coffee grounds and egg shells, then mix it all up.
Since it's not store bought, sterilized potting mix, I will have some weeding to do as my seedlings grow.
I put just over an inch of soil into the bottom of the pop bottles, then poke a hole almost to the bottom with my finger. I drop in 2 or 3 seeds, and cover them up. I write the seed type and the date on the top part of the bottle in permanent marker. Then it's time to reattach. Hold the bottom part in one hand, and squish the sides in a bit as you work the top into place. It can be a little tricky.
The pop bottle greenhouses go into the greenhouse shelves to sprout.
I started 4 starfire tomatoes, 2 sweetie (cherry) tomatoes, and 4 green peppers. If they all do well, that's all I plan to plant this year. Last year I started I planted a lot of tomatoes, and made a ton of green salsa. Not too many ripened before the frost. I think I have enough salsa to last a couple of years, at least.
This year I plan to put one tomato in each corner of the greenhouse, with a cherry tomato in the centre of each side. Aiming for red tomatoes rather than a million tomatoes.