Whether it's yellow people or yellow plants it is never a good thing. Right now the seedlings are suffering from a yellowing which started around March 4th (img_2478ed.jpg). Tomato seedlings can suffer from yellowing for several reasons such as: excessive watering, inadaquate water, malnutrition -- typically a lack of Nitrogen or other micronutrients. Since I water regularly -- once a week -- I thought that this might be underwatering but after a week there was no response. So I stopped by GreenFire for some advice. A shabby, knowledgable young guy guided me to a new product. Earthjuice Microblast is packed with micronutrients and magic good stuff for plants.
Tomato Diseases -- unhelpful for this symptom but a good link
Tomato Casual -- new favorite tomato site
Helpful Gardner -- What??? Online advice, how cool is that?