Updated: Mar 1
Fortunately, I don't have to go to such lengths to feed my little plants. But they do need some extra yummies.
Most seeds have resources to grow their germinating offspring for about ten days. After that, they are limited by what nutrients they can draw from the environment. For seedlings in a sterlized growing medium there is not much to feed them.
This is where I diverge from 'organic only' farmers. Organic fertilizers such as fish emulsion are a no-go when plants are living inside my house. Synthetic fertilizers are cheap and widely available. I usually use a 10-10-10 fertilizer powder that can be diluted in tanks and in a fertigator, watering every other week or so.
Checking in the flower farmer 'bible', Specialty Cut Flowers by Allan Armitage and Judy Laushman, it looks like most of the varieties I have in trays require 200 ppm of nitrogen on a regular basis. I wasn't quite sure how that worked out when using the fertilizer at the recommended rate - 1/2 to 1 tablespoon per gallon - but messing around with the calculator convinced me that using the manufacturer's instructions is pretty close to what is needed. [Edit: more rigourous calculations lead me to favor 1/2 to 1 1\2 teaspoons per gallon.]
Feeding the babies commences tomorrow!