Rosemary Norwood and her husband, Sean Cadman, who live in the Tasmanian valley of Jackeys Marsh, began growing the giant vegetable in April last year at their eco-tourism guesthouse.
After months of plucking away less-successful surrounding cabbages, the couple left the savoy to grow undisturbed until late January.
"It doesn't always work out like this," Norwood told CNN, attributing the success to "a good, wet spring, good rainfall and hot weather in the early summer."
Norwood kept hungry wallabies and possums out with a wire fence, and had to place the cabbage under a fine net to stop slugs and butterflies.
The toil has been worth it, however -- the cabbage ended up large enough to provide almost two weeks' worth of coleslaw, German rotkohl and salads for their guests.