Living in zone 3, I should start most seeds in March or April. But April is always extremely busy at my day job, with lots of stress and long hours. Typically, I forget to water, don't have the patience to adjust grow lights, and don't have time to carry plants outside before work so that they harden off. The few times I tried this, it ended up being a big, fat failure. I don't even try anymore.
That's why I was excited to stumble across the idea of winter sowing. In a nutshell, winter sowing is planting seeds in re-purposed plastic containers, which act as mini-greenhouses. Once planted, the containers should be put outside — even in freezing temps, and even in the snow. As the temperature warms up, the seeds will germinate, and the seedlings will stay toasty in their little greenhouses.