Starter solutions available in nurseries, are usually called something like quick start. They are diluted to keep from burning tender stems, leaves and roots.
Here's a recipe for how to make your own from OSU Fact Sheet 6007-4.
Add two tablespoons of 19-46-0 or 12-24-12 or 10-20-10 fertilizer
to a gallon of warm-ish water to dissolve thoroughly.
Apply a cup of the diluted fertilizer to each plant, but avoid pouring it directly on the plant stems.
Pouring into the planting hole before adding soil and then the plant would be ideal for a small garden, but probably not practical if you are putting in 300 eggplants or cabbages.