A Cornwall couple said they returned from holiday to find a plant in their garden had grown 26ft (8m) high.
Heather and Mike Godfrey went away for two months but came home to find the agave plant towering above the garden.
They brought the succulent when they moved to St Merryn 22 years ago but say they never expected the main stem to grow so fast in such a short time.
According to the couple, the plant's stem has grown about 2ft (60cm) a week since June.
However, now that the it has flowered, it will die - although the plant has produced some young off-shoots at its base so Mr and Mrs Godfrey could see a repeat perform in two decades' time.
Mr Godfrey said: "I came back and I dumped the suitcases in the bedroom and looked out and thought 'whoa'."
Agave plants are known for their slow maturity and for dying after they flower.