A good 4m in height, it would soon explode with bright green and ''almost radioactive yellow'' flowers, collection curator Dylan Norfield said.
But a patch of weed left to grow behind the plant tells the story of the dark side of the Chilean immigrant.
Mr Norfield said it was believed the leaves of the plant, which sport extremely sharp spines pointing inwards, trapped sheep and birds, allowing the plant to gain nutrients from their rotting corpses.
And that is why gardeners have decided discretion is the better part of valour, and let the weeds behind it grow.
''You can't get in there, because it's so vicious.''
The puya came to the garden in 2000, and is flowering for the first time.
The flower would blossom more fully in the next week or so, reach its peak in about three weeks, and bloom for about two months.
The puya could take up to 20 years to flower, and Mr Norfield said it could be years before others in a group of the plants would follow suit.
