We grow thousands of veggie seedlings a year for our garden center. Use a good-quality potting mix to start your seedlings. Compost and garden soil turn to mud when watered and suffocate the tender roots. Read the bag of your potting mix. Most provide a weak "starter charge" of fertilizer. If this is the case, you won't need to fertilize until the 2nd set of true leaves develop. This is also when the seedlings are ready to transplant into bigger containers. Once transplanted, apply a weak fertilizer at every watering. Remember to keep the potting mix moist (not soggy) so the seedlings can develop a healthy root system.

Let me know if you need more info on starting seedlings - I am happy to help!