Then NParks will make suggestions on how biodiversity can be improved or, say, what plants to grow to attract more birds and butterflies.

The students and teachers will then come up with an action plan and a plant grocery list, which NParks will go through to provide feedback before planting begins.

The planting can be done by the students or contractors.

Each school is given about a year to complete the programme.

NParks will be on hand to offer further advice during the programme. Thereafter, the schools are expected to continue to conduct biodiversity audits on their own and carry on the outreach programmes.

Ms Linda Goh, a director at NParks' National Biodiversity Centre, says the programme was mooted to bring nature closer to youth as "people who live in urban areas tend to have fewer opportunities to come into contact with natural habitats".

She says: "Students spend a lot of time in school and we hope they can learn more about Singapore's biodiversity in the natural classroom of their school compound.

"When they see and get to enjoy birds, butterflies and plants every day, they may become interested in biodiversity and want to venture out to look at and do more for biodiversity elsewhere on our island."

She adds that this encourages "stewardship in nature conservation", which is key to achieving Singapore's City In A Garden vision.

Greenery further helps students to relax and focus better, she says.

Parents welcome the idea of green schools.

Housewife Satpal Gill, 44, whose eight-year-old twin boys are studying at Hougang Primary, one of the first schools that participated in the programme, says: "They would come back and tell me stories like how the fruits in the fruit orchard had to be covered so they won't be eaten by bats and birds.

"At the least, they know that fruits grow on trees and not in supermarkets."

The Straits Times takes a look at some of these extraordinary green spaces.

Orchid hybrids created by pupils

Every nook and cranny in Hougang Primary is filled with vegetation.

A colourful butterfly garden runs along a 100m strip from the school's entrance to the carpark at the back, where there is also a fruit orchard with durians, rambutans and jackfruits.

Two green plots sandwiched between two school blocks thrive. One has an eco-pond filled with water plants, a fernery housing ferns and mosses, a rotting log habitat of fungi and a "rainforest" of trees and shrubs. The other has an animal enclosure for rabbits and chicks, as well as areas carved out for herbs, medicinal plants, and hydroponic and root vegetables.

A small empty area at the back of the canteen was turned into a nursery for pupils from the school's green club to learn to propagate plants from stem cuttings and nurse sick ones back to health.

Even the walls are utilised. Two bare onesare now teeming with greenery such as pitcher plants and ferns held in pockets stapled to the walls.

In its latest effort last year - under the National Parks Board's Greening Schools for Biodiversity programme - an eroded slope lining the back of the school was turned into a row of about 60 species of native plants, including the Leea rubra, easily recognised by its clusters of crimson red flowers; and the delicate Eulophia graminea, an orchid with unusually small flowers.

In total, Hougang Primary has more than 600 species of plants, including an orchid hybrid named after the school (Dendrobium Hougang Primary School) and another after an ex-principal (Dendrobium Sabrina James). The cross- breeding was done by pupils.

The move to become a school within a garden, as described by Mr Mohan Krishnamoorthy, level head of science and teacher in charge of the green club, took root not long after the school opened in 2000.

The then-principal, says Mr Mohan, 42, wanted an eco-garden to complement the school's science curriculum. Over the years, he says, the garden grew.

"We realised that greenery cools the environment and makes learning more conducive," says Mr Mohan. "Also, we hope that by spending years in a school surrounded by greenery, children will cultivate a love of nature and realise how plants are necessary for our survival."

The school's green club pupils are actively involved in planting, but the gardens are also an integral part of the science curriculum.

Primary 3 pupils, for instance, visit the fernery to learn about non- flowering plants - a topic in their syllabus.

To teach them about the life cycle of animals, Primary 4 pupils are given a caterpillar on a stem cutting, each obtained from the school's butterfly garden.

To cut down on the cost of greening the school - the bill has run into thousands of dollars - items such as soil, compost and the water sprinkler system were bought separately and installed. It is easier, but more expensive to hire a contractor to do everything.

With so many green areas, it was crucial to make sure that the plants were getting enough water.

The school uses a water sprinkler system with solar-powered timers set to automatically water the plants once or twice a day. To conserve water, a tank collects rainwater - enough to hydrate at least half the garden - and delivers it through the sprinkler system.

Despite how verdant the school already is, the green club hopes to make the school even greener. Mr Mohan says: "We plan to create a green wall on the water tank. We also hope to propagate native plants and share them with other schools."

A pond that cleans itself

At Bukit View Secondary in Bukit Batok, a lot is done with very little.

A fish pond surrounded by four school blocks cleans itself, with plants such as pandan, water lily and lotus acting as natural filters by "eating up" and absorbing decomposing leaves and fish faeces.

Another pond, with a man-made filtration system, is powered partially by two solar panels. A meter tracks the amount of energy used.

An overhanging pipe collects rainwater from the roof of a school block and channels it to a tank that is used to refill both the ponds, conserving water.

One of the ponds even has a water wheel to turn the kinetic energy in flowing water into hydroelectric energy, which is then used to power LED lights.

The eco-garden was created by the school's science department in 2008 as "an outdoor classroom for our students", says Mr Heng Chong Yong, 41, the school's head of department (partnerships).

It was set up back then to complement an environmental module run for its Secondary 1 and 2 students to "show them how energy and water conservation as well as biodiversity of a fish pond actually works", he says, adding that school textbooks can do only so much.

That particular module has since been replaced by another, but the garden continues to play a huge role in clean energy and environmental technology lessons. It also helps the school to distinguish itself from others, says Mr Heng.

But all this was not done without help. The garden cost $77,000 to set up - $50,000 from the Ministry of Education's (MOE) upgrading of facilities fund and the rest donated by the School Advisory Committee, comprising parents, alumni and other members of the public appointed by MOE.

A garden with seven species of plants that can attract butterflies was added in 2014 to boost the school's biodiversity - this was part of the National Parks Board's Greening Schools for Biodiversity programme.

Last year, the school also dipped into its pocket to build a $15,000 pavilion for teachers to conduct classes outdoors. Last month, it started piping nutrients from fish waste from one of the ponds to pots of kangkong in the pavilion to fertilise the vegetables.

The garden, about the size of three basketball courts, also hosts learning journeys for primary school pupils from nearby schools - two to three visits each year - with Bukit View Secondary teachers pitching in with worksheets for them.

The eco-trails, which expand on topics such as food chains and habitats, are led by the school's environmental club, although anyone interested can volunteer to lead as well.

In the future, the school hopes, through assembly talks and forums, to get more students to appreciate nature and the environment. Mr Heng says: "So far, students enjoy going to the garden to relax and chit-chat, but not that many appreciate the natural beauty around them."

But there is at least one unintended benefit of the programme so far. Secondary 2 student Calvert Choo, 13, from the environmental club, says that leading the eco-trails has made him more confident. He says: "I used to be very shy and found strangers scary. But now, I am not afraid to speak in front of people."

Nature stop for the stars

Commonwealth Secondary School's biology teacher Jacob Tan (above, in printed top) showing students water lettuce in The Wetland eco-habitat; and the Indoor Garden. ST PHOTO: KEVIN LIM

Take a walk through the "rainforest" at Commonwealth Secondary School and you would be forgiven for thinking that you are in a real one: The area between two school blocks is filled with shrubs and trees, some of which are two storeys high.

The plot, about the size of three basketball courts, is one of four eco- habitats in the school in West Coast Road. The others are a wetland, an oasis of cattails and mangrove trees which attracts birds such as kingfishers, a freshwater stream with fishes and plants, and a marine reef tank with soft corals and clownfish.

Indeed, the school is so lush that it has attracted other creatures such as monitor lizards and squirrels.

Environmental education in the school started in 2001 when a group of students and teachers, who were nature lovers, formed the Eco Club to run programmes for the school.

In 2013, teachers wanted to create habitats so the whole school could benefit. The following year, it joined the National Parks Board's Greening Schools for Biodiversity programme.

Biology teacher Jacob Tan, 31, who is also the teacher in charge of the Eco Club, says: "The eco-habitats provide students with real ecosystems to study and observe how organisms depend on one another for survival."

The heavy-lifting, such as digging works for the wetland, was done mostly by landscape companies; students were involved in other ways.

In 2014, the club hosted American actors Andrew Garfield and Jamie Foxx, who stopped by as part of the World Wide Fund For Nature in Singapore's Earth Hour events.

But the eco-habitats' impact is much more far-reaching. All academic departments have designated at least one lesson a semester that draws on the eco-habitats and requires students to visit them - a move that benefits the school's 1,300 students.

During mathematics lessons, for instance, students learn to use the growth patterns of tree branches to explore the Fibonacci sequence, a series where a number is found by adding the two numbers before it. In chemistry class, flowers gathered from the eco-habitats are mashed up to produce a mixture that demonstrates chromatography.

Students have grown so attached to the green spaces that when the wetland was invaded by golden apple snails in November last year, they chipped in during breaks and after school to help remove them - by wading through water and using tongs to pick out hundreds of snails and scraping their eggs off leaves.

The snails ate up the water plants and threatened to displace the native freshwater snails. The students' efforts paid off after five months when the population of golden apple snails was brought under control.

Denise Quek, 15, vice-president of outreach at the Eco Club, loves the green spaces, having had little chance to interact with nature as an HDB dweller. "Thanks to the many plants and animals I encountered in school, I can now put a name to the birds and butterflies I see outside."

Mr Tan, who has been a teacher at the school for more than six years, says: "Students today lack interaction with nature. Since they spend most time in school, it would be good if they can encounter nature in school and not wait until they go to the nature reserve. It is only when students feel connected to nature that advocacy and activism will emerge naturally. Without this connection, there's no point talking about global warming and related issues."