The National Botanic Garden of Wales, which opened in 2000, is to have its funding from Carmarthenshire council slashed.
The council says this is because, in part, the National Botanic Garden of Wales has not been using enough of the Welsh language on its signage and literature.
The garden will receive a grant of £70,000 this year, but that will reduce to £50,000 for 2016-17, and £30,000 for 2017-18.
The council’s executive board agreed to continue supporting the garden, on condition that it improves its use of the Welsh language, and looks at ways to become more sustainable.
It also agreed, in principle, to contribute £50,000 towards a Regency landscape project — part of a match-funding package so the garden can secure a £6.7 million Heritage Lottery Fund grant.
Council leader Emlyn Dole said: “It [the Garden] needs to change; it needs direction; it needs marketing.”
The council’s Welsh language champion Mair Stephens added: “This is an opportunity to underline that we are a bilingual county.”
National Botanic Garden director, Dr Rosie Plummer, said: “It is good news indeed that the council has pledged £50,000 towards our Regency restoration project.”
She added: “We are pleased to hear, too, that councillors have agreed to continue to recognise the important contribution the garden makes to the area and to continue to support it.”
In the past few weeks a row has erupted concerning the Garden’s use of an English-only sign to promote an antiques fair.
The Welsh language campaign group Cymdeithas Yr Iaith said the Garden failed to acknowledge the Welsh language properly, and “fell short of what is expected in the 21st century”.
It also called for public funding to be withdrawn.
Garden bosses defended the sign, saying it targeted “tourists coming from the other side of the Severn.”