Then the plant suddenly burst through the centre and grew and grew and grew, shooting up 25ft in a matter of weeks and bursting into yellow-green flowers.
It towers over owner Hermione Morrison's house and is so tall that even when she leans out of her bedroom window she still cannot touch the top of it.
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Day of the triffids: Hermione Morrison looks at the giant Agave plant which now towers over her home
The extraordinary specimen is an Agave, commonly known as a Century Plant because of the curious life-cycle which sees it flower once after decades of being dormant. Native to Mexico's deserts, the plants are now common in the Mediterranean. Mrs Morrison, 70, planted hers in her garden in Helston, Cornwall, in 1982 after she brought it back as a seedling from a holiday in Gibraltar.
As the years passed, she wondered if she would ever see it flower as Agaves can take up to 70 years before the spectacular eruption occurs. Experts believe Britain's unpredictable weather may have prompted hers to flower after a relatively modest 26 years. She said: "I didn't give it any special treatment. I just left it and it was a surprise to see it flower after so long. They can take years and years to flower and I thought I might never see it happen. But this year it's been growing several inches a day.'I knew it would be big but I had no idea it would grow taller than my house. It's absolutely massive"
Agaves only flower once before the original plant dies. During flowering a tall stem or 'mast' grows from the centre of the leaf rosette and bears a large number of short tubular flowers. A spokesman for the Royal Horticultural Society said the plant may have reacted to a series of mild winters which has protected it from frost. He said: "The plants build up their resources over the years and when strong enough shoot up a great big stem. This uses up all its energy and it dies. The run of mild winters seems to have effected agaves which is consistent with what we'd expect from climate change. Normally they would be happier in hotter climates such as Spain or Portugal but mild winters here are protecting them and allowing them to flourish".
Agaves are used to make tequila in their native Mexico. The flowers, leaves, the stalks and the sap - which is known as honey water - are all edible.