A South American plant with a 10ft (3m) tall flower spike is about to bloom in a Surrey glasshouse for the first time since it was planted 15 years ago.
The Royal Horticultural Society (RHS) at Wisley said the Puya chilensis, a native of Chile, would bloom in the next few days and last about a week.
The animals then decay at the base of the plant, acting as a fertiliser.
The RHS feeds its specimen on liquid fertiliser.
The gardening charity said very few specimens of Puya chilensis were known to have flowered in the UK.
The National Botanic Garden of Wales waited 11 years for its plant to bloom, though clumps bloom every April in the open on Tresco in the Isles of Scilly.
The plant has bright greeny-yellow flowers on tall spikes above the razor-sharp spines.
"I'm really pleased that we've finally coaxed our Puya chilensis into flower," said horticulturalist Cara Smith.
"We keep it well fed with liquid fertiliser as feeding it on its natural diet might prove a bit problematic.
"It's growing in the arid section of our glasshouse with its deadly spines well out of reach of both children and sheep alike."