The much anticipated winter rains that bring a lush green to the island mark another “season” in the gardens – the weeding season. The most prolific weed on the island is Oxalis pes-caprae, commonly known as sourgrass or Bermuda buttercup. It is native to South Africa and highly invasive in California, especially along the coast.
How oxalis came to be on Alcatraz is not known. However, it is thought that the bright yellow winter flowers of oxalis were ideal to plant with the summer blooming pink Persian carpet, Drosanthemum floribundum.
While this planning of sequential garden bloom is clever, past ornamental plant introductions often turn out to be problematic choices.
To maintain the Persian carpet and to keep it from being choked out, volunteer gardeners will be spending countless hours on the south facing cell house slope from now until April.
Weeding oxalis is no easy feat but not without rewards. Oxalis grows from a corm from a depth of one inch to over nine. Digging out the corm is the key to removing the weed once and for all, and the satisfaction of pulling out the entire corm is very rewarding. I often find myself holding up the offending corm and showing it off proudly to the volunteers, as usually it’s only other weeders who can fully appreciate the accomplishment. In addition to the sheer pleasure of weeding for hours, enjoying views of San Francisco and the Golden Gate Bridge, chatting with visitors who are also admiring the view, and occasionally eavesdropping on conversations cannot be beat.