Okay, they're still pretty young so honestly you don't need ferts yet. Most barely have their first set of true leaves. What growing medium are they in?
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Otherwise, holy sheet, that's a lot of peppers, and they look great!Â
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Edit- sorry I misread your question! I don't fert until they're in their final containers. Since you end up potting them up several times, they will get the nutrients from the soil you add when you up the pot size. I typically go from starters --> solo cups --> 2 gal --> 5 gal. I don't fertilize until they've been in the 5 gal for a couple weeks. From then on, I fert with low concentration liquid stuff (fish emulsion, bat guano, etc) mixed with water about bimonthly. As long as you use a good quality growing medium, they really do not need to be fertilized very often. Mixing healthy compost or a good organic soil (Fox Farms is pretty popular on here) will provide everything the plants need.Â
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Peppers cannot use the nitrogen in the air (N2), they can only use nitrogen in the form of nitrates, nitrites, and ammonium. Healthy soil has all the necessary components, and these compounds are made by microorganisms in the soil that the plant can use. Often, soil sold at department stores is sterilized, but by adding compost you can reintroduce a lot of the natural micro-biome of soil. This is why I don't add nutes until they stop getting fresh soil. Â