What size do you start feeding baby seedlings?

Just germinated some seeds and I would like to know what size should they be to start feeding?

Don't feed seedlings. Need more details about your grow medium to have any idea on when you should feed them at any age.

Thanks for replying, have just transplanted seedlings into potting compost and have them sitting indoors on my w/sill south facing, they are still at the two leaf stage and growing steadily. I hope to transfer them to a greenhouse when the climate suits. I'm located in N.Ireland. House temperature maintained around 20 night and day + or - 1or 2 degrees. Total beginner and at this stage don't want to outlay on growing tents, lights etc. Is it feasible. Thx

Sounds like a plan. You should wait till the plants are about three or four weeks old. Then with a WEAK solution.

I wait for the cotyledon leaves to yellow before I feed. That usually takes 3-4 weeks as Danny recommended.