When the Gardens of Alcatraz restoration project began in 2003, staff and volunteers began removing 40 years of overgrowth without a designated place on the island to compost. The removed overgrowth was hauled to the Parade Ground and added to the ruins of the former apartment buildings, already buried in vegetation. But the Parade Ground closes each bird-nesting season from February to September, so every winter there was a race to clear and deposit the vegetation; during the summer months vegetation removal still continued but a massive pile accumulated quickly, waiting to be hauled away in September. 

In 2007, the project team began restoring the Rose Terrace (read more about Alcatraz Island's roses). Situated halfway up the east side of the island, this garden area was historically the center of gardening operations and had featured a large greenhouse. Logically, the garden rehabilitation plans recommended that this area once again be used as a center of garden operations and include a composting site. Using three 4'x4'x4' compost bins, constructed with the help of Job Corps of Treasure Island, we now produce award-winning compost. With use of a chipper, woody vegetation (ivy, blackberries, roses, and other shrub clippings) removed from the gardens is shredded. This material provides the "browns" that are high in carbon. The "greens" come from spent flower heads and plant cuttings, weeds that have not gone to seed, and ivy leaves that provide nitrogen.

Sifting compost at Alcatraz Historic Gardens. Vivien Kim Thorp / Parks Conservancy

Layers of greens, browns, topsoil, and manure are piled in the bins, located in the shade. With hops from Anchor Steam Brewery and horse manure from Marin farms, each batch takes roughly one month to mature. The hops provide extra nitrogen, and with manure, the temperature easily reaches between 140 and 160 Fahrenheit. High temperatures are needed to break down the organic matter. After the temperature cools, red wriggler worms do their magic and work their way up from the bottom of the bins. Ideally, the worms stay for another month to break down the organic matter further, and in turn, add to the organic matter themselves with worm castings.

Once the batch is "done," larger fibrous pieces that have not broken down are sifted out to be used as mulch or to be put back in the next patch to be composted. The finished compost is used for potting medium-sized plants and topdressing all the flower gardens.