The majority of seedlings don't need or even tolerate fertilizers. All the nutrients they require are already in the seed coat and supplements can easily burn the roots or cause excess top growth that the roots can't support.

Once established as plants - after third set of true leaf development or when they are ready for transplanting - then any very mild, well diluted, low nitrogen supplement is usually sufficient.

There is FAQ here on feeding and lots of discussions about various brands of fertilizer that the search will pull up for you.

Dave

Fertilizer discussions

Here is a link that might be useful: FAQ on fertilizers

Tell us more about what you are trying to do, what you are growing, and at what point you are considering applying fertilizer. Are you just starting seeds indoors before they can be planted out? Are you talking about planting seeds in the ground and fertilizing them at planting? After a certain period of time? We will need to know more to be able to give you meaningful advice.

Thanks for taking time to answer. I'll check links.
I was using fish fertilizer before when growing seedlings of tomatoes (after they get true leaves and go to individual containers) and some other veggies, but this thing is very smelly.
I decided to use something different this year.

So we're talking about plants rather than seedlings and for them there are any number of good fertilizers available - assuming there is none already mixed in with your potting mix that you use in the individual containers.

In the greenhouse we use Neptune's Harvest Organic Fish and Seaweed Fertilizer once a week (diluted to 1/2 strength) for those growing organically and Bonnie's Water Soluble Tomato Plant Food (also well diluted) for the non-organic plants. Easy to use as we water the plants but never use full-strength. Numerous other brands are just as good.

With larger container plants - bigger than 4" pots - we prefer to mix granular slo-release fertilizer in with the potting mix - probably 50 different brands available, both organic and non-organic, available.

Dave

Speaking about seedlings, the method I have found best is to use stratifications with nutrients down below the seed at the bottom of the seed flat or other container that you are using. At the very bottom of a container that is approximately 3" deep, place a layer of oak leaf mold or dried bracken fern. This is primarily for drainage (obviously you will be using a container with holes or cracks for the water to escape). Above this drainage layer, lay down a half inch of well rotted cow manure. Over that manure, sprinkle a thin dusting of bone meal. Then add your potting soil (2 1/2" to 3 1/2" deep). The best mixture, in my experience, is 1/3 sifted oak leaf mold, 1/3 sharp sand, and 1/3 sifted loam soil. A 1/4" sieve is just about right.

Sow your seeds on the surface, then cover with a layer of finely sifted potting soil (as above). Remember, under cover rather than over cover. When the seeds germinate they will not be in contact with fertilizers, so will be protected from damping off, burning of roots, etc. Then, as they develope, they will sense the manure below and this will stimulate agressive root development as the plant forrages deep to reach the nutrients below.

You shouldn't need any other fertilizers until you plant out in your garden. The website below gives more information on this professional technique.

Here is a link that might be useful: Propagation using the biodynamic french intensive method

I just water with half strength Miracle Gro soluble fertilizer. Simple and effective.

I just water with half strength Miracle Gro soluble fertilizer. Simple and effective.

Thanks to all you for good ideas.
I might try different ones on different flats.

Francis, is it possible to replace cow manure with some other manure? Like horse, chicken?