Head gardener Tim Kirk and assistant head gardener Angie Silver, who are among seven staff being made redundant, said: "We have wonderful gardens, including a new British Butterfly Garden which we launched with Butterfly Conservation earlier this year, and we had the best year ever, with over 120,000 visitors through the door."
They said they were concerned about the future of the site, where they are dismantling gardens and retail and other buildings until they leave on January 15, but added that despite there being new housing built adjacent to the green belt site, the council has assured them that the former Rose National Rose Society land will not have housing built on it.
St Albans City and District Council said: "It is not a site where housing can be built. The site is not in our local plan where things can be built in the next 20 years. As for the future, it's impossible to say."
No-one at Breheny was available for comment.
The gardeners added: "We are so proud of the changes we made in the gardens, from our time here, and these were only set to improve, with a new fruit garden planned for reopening in Spring and improvements in the wildflower meadows. The 27 acre site was a haven for native butterflies and the small blue, of which was extinct in Hertfordshire and we now have one of the breeding colonies in the area (due to land management), and the site has been spotted to have over 28 species, to date. Our meadows have also provided us this year with Bee Orchids, Common Spotted Orchid and Pyramidal Orchids, so our meadow management was started to reap the fruits of our labour.
"At a time when the native butterfly numbers are so low, we beg to question why close such an important conservation and education project.
"We are so disappointed that the project has been stopped at the point at which the gardens are coming into maturity and really blooming."
The long term vision was originally to build a 100m biome to house the world’s largest walk through butterfly exhibit. After having tried for four years to secure funding for this development, Breheny said it reluctantly believes it is longer realistic to achieve this.
The gardeners said the site was "buzzing with life" and "in addition to being a great day out, Butterfly World also built up extremely successful education and conservation programmes which had enormous value to the community beyond their commercial viability".
This year more than 12,000 children from 200 schools took part in our learning programmes which were designed to support Key Stage 1 and 2 of the National Curriculum, and were hosted by experienced educators. Children held insects, saw the life cycle of a butterfly in action and experienced some of the life of the rainforest, all topics they had been learning about in the classroom.
They say they are proud of their native butterfly conservation programme that is supported by a network of wildlife organisations such as Butterfly Conservation and the Wildlife Trust.
They added: "Two thirds of the UK’s native butterflies are in decline due to habitat loss, which is particularly noticeable in places like Hertfordshire where there are so many demands on its open spaces. When Butterfly World first opened in 2009 it was a bare patch of earth with no resident butterflies. Less than five years later, 28 different British species had been recorded here, making it one of the best butterfly sites in the district.
"Butterfly World is now home to the largest colony of Small Blue (Cupido minimus) butterflies in the region, a species that was considered extinct in Hertfordshire and Middlesex for many years. The arrival of the Small Blue at Butterfly World is a direct result of providing a suitable habitat for the butterfly, which included the caterpillar food plant and sheltered areas.Professional and volunteer gardeners have designed, created and maintained all the formal and informal gardens at Butterfly World, including the opening of a new British Butterfly Garden this season. The gardeners have worked closely with organisations such as Plant Heritage, Groundworks and Oaklands College, and the team brought in sponsorships with brands such as Mr Fothergill's, Blackmoors and Bulldog.
During the summer seasons Butterfly World employed 43 people, supported by a team of more than 50 volunteers who worked in the gardens, as tour guides, photographers and more.
The project also partnered with organisations such as The Shaw Trust and Digswell Nursery.