Make one floor of every condo a "farm floor" with vegetable garden. Feed the city from the city
Local food production in your own apartment building. A designated "farm floor" could be in the basement of the building where the underground parking is/was. Powered by solar panels on the roof.
A variety of urban agriculture opportunities are being incorporated into major developments.
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hf commented
I guess this counts as a green retrofit as well. Better than building a new structure for vertical farming because vertical farming still requires mass distribution across the city.
Air purification could be a plus
LED technology makes hydroponic farming very efficient. All excess power from rooftop solar panels could reduce strata fees