Answer: Seedlings started in a sterile soilless mix will need to be very lightly fertilized to provide nutrients. Start fertilizing after they have developed a set of true leaves, which it sounds like you have done. Use a diluted formula about once a week. A general guideline is that after they are transplanted to a real soil mixture, increase the time between fertilizing to about two weeks. Fish emulsion is a good organic source of nitrogen but it is not immediately available to the plant for uptake, so it may take a bit for the leaves to green up. Don't be tempted to overfertilize, which can burn the young roots. Make sure soil is moist before fertilizing, and water after, again to help prevent burn. Also make sure your seedlings are getting enough sunlight and have good air circulation.
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