Community gardens combine several loneliness-fighting factors at once: regular scheduled contact, shared purpose, and physical activity outdoors.
Why it works well
The activity itself gives people something to talk about besides small talk, and the recurring schedule (watering, planting, harvest seasons) creates natural, repeated contact over months.
Search for a community garden plot through your city's parks department or a local gardening nonprofit — waitlists exist in some areas, so it's worth inquiring early.