If your soil contains sufficient nutrients, you only have to give em water.
If your soil needs a bump, top dress with organic nutes and scratch it into the top inch or two of soil.
Nutrient blends are the easiest way to get good results.
Bio-Live is great for mixing with soil before filling pots.
Bio-Fish is better for top dressing (and cheaper than bio-live).
Both are made by Down-To-Earth. I believe they are in Oregon.
Many things can be added as amendments but most are not complete so they can't be used exclusively.
Be careful with manure. Chicken and steer can be high in sodium if it hasn't been composted properly.
Also be careful with store-bought compost.
The stuff made from yard waste will suck nitrogen out of your soil because it hasn't been composted long enough.
And it's usually way too heavy on "brown" components, so there's no nitrogen to spare.
good luck