It still seems like the only possibly scalable solution. A hypothetical genetically engineered plant being dumped from ships in an ocean dead zone / desert, where it will do photosynthesis and drop pellets of heavier than water (nondegradeable) biopolymer to the ocean floor. No need to dump the fertilizer itself if the plant can store enough when it’s bred in a floating bioreactor. It only needs to produce polymers.
Only in the vast ocean deserts could we use exponential growth of plants and the abundant solar energy and space.




You could also drive around and chat up and ask other gardeners. Or farmers in your areas. It really depends on local climate and soil.
As for community, ideally you’d find people first who actually know what they are doing and can teach you a little.
In a temperate zone for example, you need about 250m² of potatoes to grow enough calories to survive (this is my math, please don’t trust this blindly). Plus vegetables of course. But calories are easier to buy than vegetables.