Work to remove selected vegetation from the walls of Knaresborough Castle is now underway as part of efforts to protect and preserve the historic landmark.
The work, which is expected to be completed during July, follows advice from Historic England and local experts.
The conservation programme will begin on the castle's outer walls before moving onto the Keep.
Plants with woody stems will be cut at the base and treated with herbicide, while non-woody plants will be left in place as they do not pose a risk to the scheduled ancient monument and continue to provide aesthetic value.
Roots will be allowed to die back naturally to avoid damaging the castle's historic mortar, while extra care is being taken to protect Maidenhair Spleenwort - a rare fern found in only a handful of locations across the UK - along with other important plant species.
A spokesperson for Knaresborough Castle said:
"Our priority is to protect and preserve the castle for the future. Thank you for your understanding."
Despite the work taking place, the castle and its Keep will remain open to visitors as normal throughout the project.

Main section of A59 Kex Gill route set to open 'within weeks'
Harrogate Ladies' College celebrates best A*-A results in four years
Ashville pupils heading around the world after A Level success
Students celebrate A Level success at St Aidan's and St John Fisher
Everything you need to know about Symphonic Ibiza this weekend
Eight Ripon Grammar students achieve four A*s or more
Harrogate Grammar celebrates strong A-level results
Ripon pupil overcomes anxiety to pursue Paris dream
More details revealed about Harrogate's Christmas ice rink in Valley Gardens
GALLERY: Hundreds gather at Almscliffe Crag for view of solar eclipse
Ripon Summer FunFest returns for sixth year
Extreme heat to cause disruption on Harrogate train line
Firework Championships to light up skies over Ripon next weekend
Harrogate MP calls for Lifeline changes to be put on hold
Harrogate streets targeted in £27,500 chewing gum clean-up
New co-working space opens in Ripon city centre
Harrogate Cat Rescue receives year's supply of food for 80 cats
Covered ice rink to open in Harrogate's Valley Gardens this Christmas
Ripon's Jaflong named 'Best Bangladeshi Restaurant of the Year'
Rise in number of children in care contributes to Council's £10m overspend forecast


