Last week the soil temperature in our garden at City College of San Francisco finally reached 60 degrees F, warm enough for reasonably quick germination of summer crops such as beans and squash.
The beans we put in are Purple Podded Bush beans, which are reputed to be able to grow in slightly colder soil than other garden beans. We put them in about 3 weeks ago, when the soil was in the mid fifities. The first leaves started out tinged with yellow around their edges, which looked like they had some kind of disease, but I knew that it was caused by inability to get enough nutrition in the cold soil. This week they are looking almost completely green.
Cold soils are the Achilles heel of organic gardens. My cousin, who raises organic seedlings in the Midwest each spring, in an unheated greenhouse, and then sells them to gardeners, says that they suffer more from chilly weather than they would if they were being grown with synthetic fertilizer. Why? Because organic fertilizer needs some action from soil bacteria to release its nutrients, the simple, water soluble elemental compounds that plants can use for growth.
Synthetics are manufactured to provide the compounds without any bacterial action, but at a cost to the earth. First, they require considerable petroleum energy to create. Second, they are so water soluble that the plants have to catch what nutrients they can while the fertilizers are on their way through the soil into the groundwater. So you have to apply more. Synthetic fertilizers that enter groundwater will pollute it. If they run off they pollute nearby bodies of water. If you can get your organic fertilizer from nearby sources, or make compost from wastes found on site, you can save the petroleum needed to transport your fertilizer. (Think twice before you decide you have to have bat guano from South America.)
So maybe my seedlings get a bit slower start, but I'm sure they catch up, and I feel good knowing that my garden is less of a burden on the earth.