For many gardeners in Pennsylvania, starting seeds now, would be too early. But Harlan Holmes might suggest, right now is perfect. In order to push the limits of our growing season, the veteran "backyard gardener" starts his first seeds now, February 15th, and staggers starting more every two weeks through fall.
The last frost date for the Harrisburg Area is around May 4th. Traditional thinking might have you starting cold crops such as onions, spinach and lettuce around April 15th. Holmes plants those as early as March 15th. He successfully extends the season with a cold frame and by using plant protectors in the field. He acknowledges that northern areas of Pennsylvania should not transplant seedlings outdoors until the end of March.
So I am experimenting this year. Involving my son and his friend, I mixed compost with a potting mix then filled several flats lined with "six pack" plastic containers. We planted only one flat. I am trying lettuce, parsley, and arugula. My laundry room will now do double duty as a plant starter station. The flats are lightly watered and housed on heated mats. I have them covered; both to hold in some of the humidity and to protect the flats from my cats.
Depending on the weather, I plan to set out the seedlings in March. I'll cover the plants. I'm interested in heat caps or blankets. More on that to come.