When to Start Seeds?

1. What's your average last frost date? The rule of thumb is to start seeds 6 weeks before the last frost date so that they're ready to set out. You might be able to start the seeds in the house 8 to 12 weeks before and have them hardening off in the green house for the final few weeks. Some of that will depend on what seeds you're planting.
2. What are you planting? So plants tolerate cool weather better than others. Peppers aren't happy if it gets below 50 degrees at night, and some tomatoes don't like it. There are some tomatoes that tolerate cool temperatures well, though. Usually the variety description indicates whether or not it tolerates cool temperatures.

Most greens and some herbs, like dill or cilantro, tolerate cool temperatures well, too.

I'll start some Stupice tomatoes in about mid-January inside the house. I'll pot them in gallon containers and move them to the cold frame around the first of March. I'll watch the weather forecasts for the next couple of weeks while they harden off, and decide if they go into the garden right away or wait until our official last frost date of the first week of April. One or two cold nights can be handled with Wall O' Water containers or by just wrapping the plants in a blanket.

Peppers don't get started until mid-February, the ground needs a chance to warm up before they get set out. Most of the tomatoes will be started then or a week or so before. The dill and cilantro will be started with the first wave of tomatoes, squash and cucumbers a couple of weeks later.

I hope I haven't confused you, but one planting date for all the vegetables just doesn't work for me.

Penelope

What does "harden off" mean? And how do you accomplish this, "hardening off"?

Lots of info here:

Hardening off is simply allowing the plants to acclimate to the change in growing conditions between where they were started and where they'll be grown.

In my case, seeds are started under artificial lights on seed warming pads. When I move them outside, they need at least a few days to get used to the more intense natural sunlight and to the fluctuating temperature. If I were to put them straight into the garden from the house, the leaves would most likely be sun burnt, the plants would most likely get shocky, and some would die. A gradual transition makes for happier, healthier plants.

Here's a site that might help, too: