Fertilizing seedlings?

Hey I have a question.  Say I have a 3 week old seedling which I grew in 75% peat and 25% vermiculite.  Then I transplant it into a 4" pot with more peat and vermiculite.  It has a couple sets of true leaves.   Don't I need to fertilize it with some liquid fertilizer?  Nitrogen only type?   Say it's a tomato plant.. I start in a cell which is 36 per 1020.  It'll grow for like 2 months before I transplant well after last frost.. so it will have to be transplanted into say 4" pot.  It needs fertilizer right?  Or do I transplant it into pot with compost and/or wormcastings ?   Just concerned about fungus gnats in the house.

If I should do the liquid nitrogen fertilizer, which one is a good and affordable?  I'm pretty frugal.

Hey Jennifer, I think you're right along the lines of your thinking and those seedlings need something. I personally would opt for a blend of compost and worm castings - it's gentle and contains microbial life. If you prefer to use a fertilizer, may I suggest liquid fish + kelp, the hydrolysate kind. I am currently using neptunes harvest brand in my garden just so I can put food on the table while I spend several years healing and nurturing my garden soil and waiting for wood chips to decompose. I would shy away from nitrogen only types.

I would mix a little rabbit poo in with your mix and then top it with some good compost.  The compost could be as simple as leaf compost.  Then I would cover the compost with wood chips.  The compost will give it good bacteria and the wood chips will slowly release nitrogen.    I do this with my stevia every year.  Stevia has to winter in the house here and seems to not get growing good till I do the above to it in the spring. Worm casting do work for nitrogen to. There are some real good homemade recipes on here to make compost tea.  Most of the compost teas are strong and I use sparingly diluted with water.  I don't use any store bought nitrogen on our food crops, so not much help there.  Good luck.

Once your seedlings have 2 true leaves  (not the first two that pop out of the soil. The second set that actually look like that plant leaf.)  you need to feed the plant. When I re-potted my seedlings I potted them in 100% organic compost. Every second or third water I would use fish/kelp organic fertilizer at half recommended strength.  To water I would fill a plastic tub thing I had from the dollar tree, I think it's for dishes.  I would fill it an inch or two with water and the fish/kelp, and put seedling pots in for a while.  When they feel heavy I would take them out.  This worked very well for me.  I was very happy, because this is my first year starting veggie seeds, and I didn't realize they needed to be fed so early in there growth, my seedlings looked very sad.  I was worried my ignorance would make week unhappy veggies.  Nature is sometime forgiving, my veggies grew healthy and strong and are starting to produce.  I hope some of this helped.  Good luck to you.

Thanks for all the replies.  I hear from various gardeners not to use compost in the house because of the fungus gnats.  I started several seedling in a mix of peat, vermiculite and compost and well I got a lot of fungus gnats.  I put a bunch of the yellow sticky tape on plant tags in teh seedling trays.. seems to be working well as I see hundreds of them stuck to it and only a sparse amount flying freely over the seedlings when I move the trays.