The majestic domes of Gardens by the Bay have been a fixture of the Marina Bay skyline since the opening of the Gardens in June 2012. It has received more than 33 million visitors to date.

A lot of work goes into maintaining the lush tourist attraction that houses close to 1.5 million plants from all over the world.

Much of it actually takes place behind the scenes, such as at the Flower Trials Centre, a temperature-controlled greenhouse where staff from the research team test and observe new species and hybrids to decide which blooms are to be displayed in the Flower Dome.

It is an ongoing process as the floral displays are changed six to seven times a year.

During the changeover period, staff set up the new display and perform routine maintenance work. Aside from the one day a month when the Flower Dome is closed for this, work takes place through the night.

Ms Marziah Haji Omar's team has put together about 30 floral displays to date.

The assistant director of flower field design told The Straits Times: "We can start work only after the Flower Dome is closed to visitors at 9pm, and we work through the night until 3am.

"It often feels like we are running solely on adrenaline and passion, but there's a special satisfaction that's hard to describe when we return on the opening day and are greeted by the sight of a flower field in its completed glory, basking in the daylight, all ready for visitors."

Beyond curating flora and fauna from around the world, the research work also involves hybridisation to produce interesting cultivars.

As for the Cloud Forest conservatory, plants near the peak of the 35m-high Cloud Mountain are maintained once every two to three months, and the work takes about two to three weeks to complete.

Plants in the lower areas are maintained once a month when the Cloud Forest is closed to visitors.

The facades of the two cooled conservatories - the domes - also require washing three times a year.

At 38m high, the 1.2ha Flower Dome is made up of more than 3,300 glass panels, while the 0.8ha Cloud Forest is 58m high and has a facade with more than 2,500 glass panels.

Maintaining such a massive tourist attraction requires many green fingers.

When it opened, the Gardens started a volunteer programme as a way to engage the community and inspire people to get involved with nature.

There are currently more than 800 volunteers who contribute in different areas, such as helping out at events, facilitating workshops, conducting guided tours for visitors and carrying out bird surveys for research purposes.

Ms Angie Ng, who is in her 40s, has been a Gardens by the Bay volunteer since 2013.

She volunteers six times a month. She said: "I get to pick up a lot of new horticultural skills because I have the opportunity to carry out soil tests, water tests and pruning to present the best shape for plants."

But beyond being an Instagrammable tourist attraction, the Gardens also stresses environmental sustainability. At the biomass power plant, horticultural waste from the Gardens and around Singapore, as well as wood waste, are burned to generate energy to power the chillers in the Flower Dome and Cloud Forest.

The energy generated is also used to chill the water in the pipes running below the ground slabs of the conservatories.

At the same time, solar panels on the canopies of some of the Supertrees harness the sun's rays to light them up at night.

To celebrate the Gardens' fifth anniversary this year, the first weekend of June will see activities such as a Gardens Extravaganza Special evening show at the Supertree Grove.

At the Flower Dome, the Blue Beauties floral display, which showcases blue blooms such as hydrangeas and delphiniums, is on till June 30.