Rainfall expected February 12-14.

Rainfall expected February 12-14. Photo: BoM

ACT gardeners aren't the only ones looking forward to a wet weekend, with the National Arboretum desperate for rain after the territory's recent heatwaves.

At least 10 of the National Arboretum's more than 48,000 trees have died and volunteers have been called in to help water, following the extreme temperatures the ACT has sweltered through this summer.

But help is on the way, with rain forecast for the rest of the week after a cool change on Thursday afternoon.

Total rainfall forecast for next eight days.

Total rainfall forecast for next eight days. Photo: BoM

The Bureau of Meteorology said up to 20mm could fall at the weekend. The territory has had just 29.8mm of rainfall in December, January and February, less than one-fifth of the 165mm average.

Until the rain falls though, arboretum general manager Jason Brown said their staff will be using up to 80,000 litres of water a day to keep their plants healthy and cool.

But not every tree has made it through the dry spell, with Mr Brown confirming at least 10 plants had died in the high temperatures.

Areas to receive NSW government drought help.

Areas to receive NSW government drought help. Photo: NSW government

''We have had a few casualties from the heatwave,'' he said. ''Once you get into temperatures in the high 30s day after day and after that's coupled with the wind, plants dry out quickly.''

Volunteers have been called in and three tankers rolled out in an attempt to keep as much of the plant collection alive and well throughout the extreme weather.

The majority of the arboretum's water comes from bores and dams, including the two-megalitre tank at the top of Dairy Farmers Hill.

Last six months: rain in Australia falls mainly in the west.

Last six months: rain in Australia falls mainly in the west. Photo: BoM

''We've got some plants that are obviously from the northern hemisphere and some of those plants have been grown in Canberra before, some have not. We're monitoring them very carefully,'' Mr Brown said.

The story is better over at the Australian National Botanical Gardens, where the completely native foliage has survived, and even thrived, in the heat.

General manager Peter Byron said their collection was adapted to Australia's sometimes harsh environment.

''It does mean our horticulturalists are busy,'' he said.

''But we're a native collection, 100 per cent native plants, and they're adapted to the climate and dry spells.'

He said the rainforest section of the gardens had become so well established it had formed its own micro-climate and was about 10 degrees cooler than the rest of Canberra.

According to Mr Byron, the gardens have an allocation of 170 million litres of water a year from the lake, but even with the heat there was little chance they'd exhaust it.

''We're not tracking on getting anywhere near that target,'' he said.