Wear and tear on the landmark hanging sculpture and its fixings were detected in the latest annual engineering inspection.
Engineers say there is significant fatigue on one of the fixings on the sphere and the aluminium has started to tear. Their advice is that the sculpture has to be removed so it can undergo a thorough assessment before being repaired.
Wellington City Council's Arts and Culture Portfolio Leader, Cr Ray Ahipene-Mercer, says Ferns, by Christchurch artist Neil Dawson, was installed in 1998 and has since become a popular subject for photographers and tourists.
"It's a magnificent piece of art and a significant focus in the Square - but it does take a real battering from the wind - and after 13 years we need to get it down and repair it."
City Council Projects Officer Vikki Muxlow says regular maintenance of the 200 kg sculpture was initially scheduled following the Rugby World Cup - primarily to replace support wires - "but the latest inspection means we can no longer wait until after the tournament.
"Once we get it down we can quickly assess the full extent of the wear and tear, and then get it fixed and back up as soon as possible," says Ms Muxlow.
Council staff and contractors will make a last-minute 'call' on wind strengths this evening before deciding to go ahead with the removal. If the wind is too strong then the project will be postponed.