Warming temperatures across New Zealand will help invasive plants flourish in what is already one of the world's weediest countries.

Lincoln University Professor Philip Hulme says climate change will help more plants to jump the garden fence and colonise the world beyond.

Hulme, of Lincoln's Bio-Protection Research Centre, was awarded the Hutton Medal by the Royal Society Te Apārangi at the annual Research Honours Aotearoa dinner, held in Dunedin on Thursday night.

The award was for his work on plant invasions in New Zealand, especially why and how exotic plants become invasive weeds.

Hulme told Stuff weeds were not just plants growing where they were not wanted in a garden, and the problem was only going to get worse due to climate change.

"Weeds are pernicious, persistent and have an ongoing negative impact.

"We have quite a few succulent species which are good in drought conditions but quite restricted at the moment as they can't deal with frost. But with drier conditions, they will take-off big time."

Areas like Christchurch's Port Hills would be especially susceptible to invasion from these aeonium species, he said.

Although billions of dollars were spent managing pest plants annually, they remained one of New Zealand's biggest and most difficult environmental issues, and were often resistant to herbicides.

Control efforts could actually exacerbate the problem by disturbing the soil and spreading seeds and roots.

These plants smothered and replaced native flora, affected soil stability and composition and also groundwater, and could heighten the risk of fire.

The worst weed beyond the garden depended on the ecosystem where you lived, with thistles among the worst for pastoral farmers, Hulme said.

"Old man's beard and blackberry are problems throughout much of the country and colonise bush fragments where they can swamp the vegetation.

"In the north, kahili ginger and tradescantia are big problems in forest, whereas Darwin's barberry is a problem in forest in the South Island.

"Open grasslands across the country are beset by species such as broom and gorse. In the South Island high country, wilding pines and lupins are big problems."

Lagarosiphon was also a national problem in lakes and rivers, Hulme said.

The worst garden weeds included creeping oxalis, onion weed, periwinkle and ivy.

New Zealand had more exotic plants than almost anywhere else.

According to the Royal Society citation, Hulme's work has focused on how botanic gardens, ornamental nurseries and the pastoral sector have helped plant invasions. 

He said it was only a matter of time before more exotic garden plants became escapees and a problem.

Concern about noxious plants was not a recent thing.

"We had noxious-weed lists as early as 1850. Thistles were way up there on that and gorse was recognised quite early on."

Australia's national approach to weed eradication, with a weeds of national significance programme, had been a better approach than New Zealand's focus on regional control work.

Invasive plants were no respecters of land borders, Hulme said. 

"That means they can set major targets across the whole of Australia."

On this side of the Tasman, regional councils, the Department of Conservation, community groups and private landowners were all dealing with similar issues.

"Much of the work across these organisations is uncoordinated and too short-term to have any lasting impact.

"Planning for weed control should be optimised by involving a coordinated effort and funded over a period of 10 to 20 years, rather than simply the next financial year as resources allow."

The Hutton Medal takes its name from geologist and zoologist Frederick Wollaston Hutton (1835 to 1905), the first president of the New Zealand Institute in 1904.