|Plastic Bin "Cold Frame"|
Instead of many small containers, I purchased a plastic bin and some seed trays. It's Maine in March (Zone 5a), and I wasn't 100% sure it would be warm enough yet to keep seedlings outside. The bin makes moving the seedlings very easy.
|Week One Seedlings|
The trick is to keep the temperature inside the bin somewhere between 60-75 degrees Fahrenheit and to give the seedlings enough sunlight to thrive. My south-facing porch seems to be working so far.
I bought a $3 thermostat to keep inside the bin. That helps me track the temperature. Sometimes, despite the 30 degree (or below) temperatures outside, the inside of the bin reaches 85-100 degrees. When this happens, I just prop the cover open to let things cool down a bit.
As soon as the sun starts going fading, the temperature inside the (uninsulated) bin drops quickly. I've just been bringing the bin inside for now. Hopefully, in a week or two, I'll be able to leave the bin outside even at night.
After a week, the kale, shallots, and basil have decided to show themselves. I'm still waiting for the peppers and parsley. Still a long way to go before these babies can be planted, but I'll keep you posted!