The private courtyards, where deals are struck among the rhododendrons and plots are thickened beside the azaleas, appear oases of tranquillity in contrast to the frenetic activity inside.

That was always the plan.

The 17 courtyards, each with a different feel, were designed to complement the building, which is linked by glazed walkways so light floods through and it feels like you are walking through one giant garden.

They provide pleasure to those inside and a challenge for the 19 staff in landscape services. It's their job to keep the gardens pest-free and blooming - without poisoning the public, the politicians and others who use the building, the courtyards and the 30 hectares of public gardens outside.

Leanne Clarke, a senior horticulturist at Parliament House, is in charge of integrated pest management (IPM), so she brings in bugs that eat the bugs that attack the plants.

''We've been doing it fairly seriously for over ten years,'' she says. ''We needed to introduce that sort of system here, the way that Parliament House is, to keep the workers, the public and the politicians safe.''

Paul Janssens, assistant director of landscape services, explains chemical spraying had been a costly, logistical ''nightmare''.

It could only be done on weekends, after turning the airconditioning off in the vast building where people work 24/7, and after covering the many air vents.

IPM is healthier for people, the environment, the budget, the garden and its beneficial for insects, he says.

He says IPM isn't entirely about bugs.

It's also about choosing resistant plant varieties, good gardening practices, feeding them the right food and selecting the right turf.

By reducing the chemicals you are allowing the natural predators to build up but that is not always enough, Ms Clarke says. At the start of spring, she put out two buckets each containing 10,000 predatory mites.

She also has regular monthly orders of bugs coming in from insectories, mostly in Queensland.

''We import specific beneficials - for example for mealy bug we are getting the cryptolaemus lady beetle and we bring in a green lacewing, it is a voracious eater of lots of things like mites, aphids and even caterpillars.''

At insectories, pests are bred up, then the beneficial bugs are allowed in and they breed up until there is an average number per leaf.

They are packed into small containers and couriered to Canberra where Ms Clarke meets them so they aren't accidentally killed in the x-ray machines that scan parcels at Parliament.

Once the bugs are released, Ms Clarke makes regular checks in the gardens and records their numbers to make sure balance is being maintained.

It's not a perfect system but when the numbers of aphids start to build up there is a time lag before the ladybirds hatch to eat them, so alternative methods are employed, she says.

''I reduce the numbers with soap spray - that will give the plants a bit of a break and as it warms up the numbers of ladybirds build up again.''

The gardeners also bring in parasitic wasps, which lay an egg in the aphid.

''The aphid gradually turns from bright green to golden. They are referred to as aphid mummies, and once that egg matures the wasp comes out and finds more aphids.

''It's not the cane toad issue where beneficial insects may become a pest, because they are very specific in what they eat'' she said.

''They will die if there is no more food source, or it gets cold.''

For scarab beetle in the turf, the gardeners get nematodes from nearby Queanbeyan, watered into the turf at night in January, they wiggle down through the moisture in the soil till they detect the scarab grubs, Mr Janssens says.

He says there are 33 hectares of gardens in and around Parliament House, 10 of turf and 13 of gardens, all maintained via IPM.

Most of them are open for public viewing and the gardeners conduct tours of some of the private courtyards during Canberra's flower festival, Floriade.

They are worth a look and some of the plants that grow there will surprise you.

The whole building acts as a heat sink because of the vast heated basement, and air vents in the courtyards, so plants that would not tolerate Canberra's frosty winters can be grown. AAP