Last week we started just over 2,000 onion, leek, and shallot seeds, plus a few cardoons and a couple of heirloom varieties of celery. And after just 24 hours, the sprouting began! Within five days, all of the seeds had sprouted.
This time last year, our onions and celery took weeks to sprout. Why such fast germination this time around?
First, we followed Eliot Coleman's advice and did not cover any of the seeds, but left them all sitting on top of the soil exposed to the air. According to Coleman, this allows the seeds to have much better access to oxygen, which is critical for germination.
Second, rather than heating the air we're using a propagation mat to heat only the soil in which we're starting seeds. (Ours is a Pro-Grow mat, available here). This is a much more energy-efficient way to ensure that seeds have what they need to germinate, since soil temperature, rather than air temperature, is the critical factor in germination time. Soil temperature without a heat mat will be 10-20 degrees lower than ambient temperature, so you would have to get the air temperature up to 95 or so and keep it there to maintain the 75 degree soil temp ideal for germination for most garden vegetables. The heat mat prevents temperature fluctuations (a big problem in our passive solar hoophouse) and allows you to keep conditions just right for the short period of time needed for germination. Then you can move the plant babies off the mat into a less controlled environment once they're up and growing.
Third, after our experience starting our winter greens in soil blocks rather than black plastic cell packs, we decided to do most of our germination for the Spring in mini-blocks. These 3/4 inch homemade blocks allow us to fit somewhere in the neighborhood of 2,300 seeds on the germination mat. So we germinate seeds in the soil blocks, and then step the babies up into bigger containers without bottom heat. It's a far more efficient and speedier system than starting seeds in cell packs in the hoophouse, which was our old method.
The eventual goal is to have a well-insulated unheated greenhouse where we can start seeds on the propagation mat, but for now the plant babies are growing just fine in our kitchen. We'll have onions in the ground in early April if all goes according to plan...til then, it's so heartening to see the tiny plants curling up from the soil. Spring is coming!
Heirloom Torpea Rossa onions (also known as Torpedo Red Bottle onions) sprouting.