Yes, they have germinated in a soilless mix, now they need some food.

How big are the seedlings? They do not need fertilizer until they get their 3rd set of leaves. Then I'd give them 1/4 strength of a water soluble fertilizer when you water. As they grow bigger you can increase the fertilizer to what's recommended on the fertilizer box. Too much fertilizer too soon can be detrimental to the plants.

I’m just looking for organic and nonorganic fertilizer recommendations, not how/when to apply them. What’s everyone’s favorite brand?

I usually use Miracle Grow (the blue granular form) or a store brand equivalent dissolved and diluted to about quarter strength. I've used Home Depots' store brand and a few other similar formulations and was satisfied with all of them.

It's not a matter of a "favorite" brand :-) Fertilizer is fertilizer and they all work the same.....the plants don't care what name is on the bottle!!

Having said that, while they may all work the same, not all fertilizers are the same so that is where the distinctions should be made. Most plants absorb nutrients in a pretty uniform ratio of 3 parts nitrogen to one part phosphorus to two parts potassium regardless of what stage of growth they may be in. So looking for a fertilizer that offers NPK in that ratio (3-1-2) is optimum. Both the Miracle Gro and the Dyna Gro offer that ratio. And they both offer a pretty full range of micronutrients as well although I am not sure how critical they are for the seedling stage. But to be perfectly honest, any liquid or water soluble fertilizer would work and I doubt you could tell a difference.

For seedlings in containers, stay away from organics, unless something in a liquid form like fish emulsion or liquid kelp.

So far on this thread I’ve learned that organics are not really the best option unless I look into fish emulsion or kelp and two good brands to consider are miracle gro and dyna gro, and that I should be looking at an NPK ratio of 3-1-2.

James - I've used the Miracle grow liquafeed Tomato and Veggie formula (9-4-9) at about 1/3 strength for my seedlings for many years. I add about 1/2 tsp. per 1/2 gallon of water and bottom water with it. I use it every time I bottom water and all of my vegetable seedlings do great.

Note: If you buy some make sure you get the 2 bottle package that has a little dispensing spoon attached. It makes it much easier to measure out the amount.