I've been lucky enough to germinate some dahlias, felicias, lobelias, petunias and antirrhinum. The seedlings seem to be doing quite nicely and the dahlias look like they are about to put our their second set of leaves (other than the seed leaves) - the others are still tiny.
All I am doing is watering them. When should I start feeding them, if at all? And can anyone recommend a reasonable food, please?
there is no need to feed them until you pot them up when they are large enough. Even then you will have a few weeks of nutrients in the potting compost before any feeding is required.
You will only pot them up into a very small pot of course, with multipurpose compost, and when 8cm (3") high transplant into borders at the end of May if frosts are not likely, but gradually harden them off first in a cold frame for about 3 weeks. Good luck.