Composting on Alcatraz

Gardening and composting go hand in hand. Aside from the obvious benefits of returning organic matter back into the soil, recycling the garden vegetation on the island is especially important as once materials come to the island, they very rarely leave.

With the gardens, our composting system has evolved as well. When the project began in 2003, there was no designated place to compost the 40 years of overgrowth. The removed vegetation was hauled to the Parade Ground and added to the ruins of the former apartment buildings that were already being taken over by vegetation. With the parade ground closing each bird nesting season from February to September, each winter there was a race to clear and deposit the vegetation, then during the summer months work would continue and a massive pile would soon accumulate, only to be hauled away at first chance in September.

Large pile of garden vegetation in September. Photo by Shelagh Fritz

In 2007, restoration of the rose terrace began. Situated half way up the east side of the island, this garden area was historically the center of gardening operations with a large greenhouse. Logically, our rehabilitation plans recommended this area to once again be used as a center of operations, including the site of our compost.

With use of a chipper, woody vegetation (ivy, blackberries, roses and other shrub clippings) are shredded. These materials provide the ‘browns’ that are high in carbon. Our ‘greens’ come from spent flower heads, weeds that have not gone to seed, and ivy leaves that provide nitrogen. Chasmanthe floribunda also provides an excellent supply of greens but these plants require the extra work of hand clipping into smaller pieces for a quicker breakdown.

One volunteer in particular, Dick Miner, is our chief composter. Using three 4’x4’x4′ compost bins constructed with the help of Job Corps of Treasure Island, Dick produces award winning compost.

Dick checking the temperature of the compost. Photo by Shelagh Fritz

Each batch takes roughly one month to mature. The bins are located in shade and we rely on high temperatures to break down the organic matter. Dick regularly brings hops from Anchor Steam Brewery and horse manure from Marin farms. With the addition of chicken manure and topsoil the temperature easily reaches between 140 – 160 F. The highest temperature achieved has been a steamy 170 F.

After the temperature cools, red wriggler worms do their magic and work their way up from the bottom of the bins. Ideally, the worms are left for another month to add to the organic matter.

Hard working red wriggler worms. Photo by Shelagh Fritz

Once the batch is ‘done’, volunteer groups, especially kids, have a chance to get their hands dirty by sifting out the larger fibrous pieces that have not broken down, sorting out the worms and putting them back in the bin. For kids that have never held a worm before, it is amazing to see squeamish kids going home to ask for pet worms for their kitchen scraps.

Dick showing off the worms to kids. Photo by Diana La

Dick has also successfully experimented with composting oxalis! Volunteer gardeners separate oxalis from other weeds and deposit the corms and green tops in a designated pile. A season’s worth of oxalis is constantly turned and manure is incorporated. With consistently high temperatures, the corms are exhausted. The oxalis compost is tested for weed seeds by placing flats of the compost in the greenhouse, labeled, watered and monitored for any growth. We have never had any oxalis return.

The weed seeds that do return are commonly wild radish, Raphanus raphanistrum, and American nightshade, Solanum americanum.

The docent tour does take a stroll by the compost bins and Dick is usually there to let you feel the rich soil. Otherwise, be sure to look over the rose terrace railing to see the compost, you can only detect it with your nose when the bins are turned.

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