The Miami Beach Botanical Garden is 2.6 acres. That is the first thing to say, because the word botanical does a lot of work in people's heads and this is not Fairchild. Fairchild Tropical Botanic Garden is eighty-odd acres of the mainland, forty-five minutes away in Coral Gables, and it is a half-day with a tram. This is a walled city block behind the convention centre that you can walk in twenty minutes.
Once that expectation is set, it is one of the better free things on the island. It was founded in 1962 on land the city owned, ran for decades as a pleasant municipal garden, and was reworked in 2011 by the landscape architect Raymond Jungles into something considerably more designed. Jungles builds with density and level change rather than lawns: paths that turn, planting that closes over your head, water at ground level, and views that only open when you have walked far enough to earn them. On a plot this size that is exactly the right strategy, because it makes the garden feel much larger than the map says.
What is in it: palms and cycads in quantity, bromeliads, orchids, native Florida trees, a Japanese garden with water and stone, a wetland pool planted with mangrove and pond apple, and a broad lawn that does most of the event work. The wetland section is the one to slow down at — mangrove and pond apple are what stood here before any of Miami Beach existed, and seeing them planted deliberately in the middle of a resort city is a quietly pointed thing.
The real argument for it, though, is thermal. South Beach is a hot, treeless, reflective place between June and September. There is no shade on Ocean Drive, none on the sand, and not much on Lincoln Road. This is a dense canopy over paved paths, ten minutes' walk from Lincoln Road, and it costs nothing. In August that is not a minor amenity.
Admission is free. Private events do close it, and that is the usual reason somebody finds the gate shut.