Answer: I use diluted fish emulsion as a fertilizer for my containerized plants and they seem to get all the nutrition they need. If you compost, you might try making some compost tea (steep finished compost in a bucket of water). It's difficult to tell just how strong your compost tea will be; the results will depend upon what's been composted and how long you allow it to steep, but it might be worth a try. Here's how I make compost tea:
You'll need some nice, finished compost (you can tell its 'done' when you can't recognize any of the original ingredients and it looks and smells like great, rich, black, crumbly super-soil; the best compost is generally at the BOTTOM of the pile).
You'll also need a porous cloth or cloth-like container--an old sock for small, houseplant-sized batches (which you'd make in an iced-tea pitcher sized container); an ugly old pillowcase (for a trash can half filled with water); or a gunny sack/feed sack kind of thing (for dunking in a 50 gallon container).
Put the compost into the porous cloth container of choice, tie it closed, and then put that into your container filled with room temperature water. Soak for 24 hours. You want the finished liquid to be the color of strong coffee; play with the amounts (more compost, more water...) until you get there.
Dilute the tea with water until it's the color of real tea. (Do not drink, however.) You can feed plants with this tea by pouring it right onto the soil around the plant, or you can strain it, put it in a sprayer and use it as a foliar feed.
Best wishes with your containerized plants!
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