Dale Toten spent a year tending his big brassica from seed to nearly 6st (38kg) at Ston Easton Park, near Bath.
He planned to exhibit the mammoth vegetable at this weekend's Malvern Autumn Show.
But although the cabbage was supposed to be off-limits, an unwitting chef turned it into a confit for guests.
Mr Toten, from Radstock, Somerset, who is senior gardener at the four-star country house hotel, said the cabbage had taken a year to reach that size.
When he found a large part of it had been hacked off, he went to investigate who had done it.
"I looked in the chef's pantry and it was right there in front of me - he had used it for a confit," he said.
"I might have lost my temper at that point. He did get an earful off me."
He estimates the cabbage, which was a Cornish Giant variety, measured 6-7ft (1.8-2.1m) across and has now warned all chefs not to tamper with any of his other prize specimens ahead of the show, even tasking his dog with watching them when he is not around.
He added: "It was an agency worker who did it as the others all know not to touch my vegetables but I have had a word."
Fortunately he has other large vegetables to enter in the show, including a 10st (63kg) marrow, leeks, onions and several other cabbages.
Nick Romano, operations director for Ston Easton Park, said: "Cabbage-gate has been a very serious incident here at Ston Easton Park and we are now in the process of implementing special measures to ensure that this never happens again and that Dale's prize vegetables are kept safe and sound."
A gardener is feeling hacked off after part of his giant cabbage was cut from a hotel garden by mistake and cooked by chefs at its restaurant.