Autumn is upon us, which means it is time to plant your sweet peas, broad beans and lettuce so they can establish well before the frosts. Or is it?

Across Australia backyard gardeners use time-tested planting schedules to ensure a good yield, but no place is more inextricably linked to the seasons than Canberra.

Newcomers to the city will be quickly told that Anzac Day signals the time to turn on the heater and not to even bother planting tomatoes until after Melbourne Cup.

But as the capital last month recorded the hottest March ever, the unseasonably warm days have also had an effect on how and when to plant.

This weather rock is tongue in cheek, but emblematic of the current erratic weather. ( ABC News: Kate Midena )

"Climate change has most definitely affected the timing of those established rules of when you plant and when you don't plant," Dr Steven Crimp, a climate applications scientist from the Australian National University said.

"Some of the old rules we've relied on for growing crops need to be revisited."

Among many changes Dr Crimp noted, an increase in frosts in September and October, a lack of steady rainfall, and warmer minimum and maximum temperatures had contributed to battered copies of the Canberra Gardener rule book being thrown off shelves.

"The warmer temperatures have people continuing to plant well into autumn and winter, because the soil temperatures are warm enough to sustain the crops," Dr Crimp said.

"But while the temperatures are conducive to planting, the rainfall is not."

It's getting hot in here

Geoff Foster and his dog stand amid his recently harvested tomato plants. ( ABC News: Kate Midena )

Of course, it was not just keen backyard gardeners who had noticed the effect of erratic weather events.

"We've had a lot of evaporation and not enough rain," Geoff Foster from Jerrabatt Gully Organics in Bungendore, just outside of Canberra, said.

"The soil's as dry as a chip at the moment."

But for Mr Foster, who grows and sells a range of produce through a subscription-style weekly delivery service, the weather was more than just an annoying, unpredictable frustration.

The heatwave the region experienced in January saw a lot of Mr Foster's crop fail, particularly his tomatoes.

"This year we look like having a 50 per cent drop in overall tomato production per plant per bed," Mr Foster said.

"In spite of trying to plant more, we're getting less per plant."

Chris Fowler from Bywong Garlic stands in front of a rain gauge at his crop. ( ABC News: Kate Midena )

Chris Fowler, who operates Bywong Garlic, ran into a similar problem last winter.

"When I reflect on last winter and the winter before, I remember walking around in short sleeves for most of the time. I don't call that a cold winter," Mr Fowler said.

"And in the harvesting period, between about middle November to early December, it's getting too hot for me to sustain green leaf on the plants.

"So I have brought planting forward from April into March. I've also brought my late season crop forward."

Mr Fowler had observed the slow change in his soil over a number of years.

"When I first came here we had a 100mm of soil moisture depth most of the year, except for the hottest part of the summer. Now I would say it's 25-30mm for most of the year," he said.

"Because I don't run stock, I used to mowed these paddocks. I haven't done that now for five years because the grass doesn't grow as well.

"It is dry, there's no soil moisture depth."

When it rains, it pours

A sudden downpour of rain at the Southern Harvest Farmers Market in Bungendore. ( ABC News: Nick Haggarty )

Ruth Gaha-Morris is the vice president of the Southern Harvest Association, an organisation that represents local growers and runs a weekly farmers market in Bungendore.

"Most of them are struggling," she said.

"We have hotter summers, bigger storms, rain at times when we never used to have rain and then no rain when we expect to have regular rain."

Ms Gaha-Morris said the producers she represented and spoke to all shared a few common experiences over the last few years.

"One of the biggest issues is the erratic weather patterns that we're having, and extreme rain rather than regular rain," she explained.

"When it's dry they're searching for water and when it's wet they're trying to save their crops and their animals from water damage that happens with large storms.

"We'd rather have regular rain like we're used to … but these days it's just massive big dump."

Dr Steven Crimp says that climate change forces us to rethink when and how we plant. ( ABC News: Anthony Bowler )

In Bywong just a few weeks ago, Mr Fowler experienced that kind of rain on his garlic crop.

"I had 31 millimetres in 10 minutes, which flooded the place, but when the water had gone you'd never have known it had rained," he said.

"Because you don't get the gentle soaking rain over a period of time you don't get that soil moisture.

You can't rely on rainfall at a particular period of the growing of the crop, so you have to water on a more regular basis."

Is better irrigation the solution?

Geoff Foster has set up an irrigation system for the crops he grows outside. ( ABC News: Kate Midena )

Ms Gaha-Morris said almost every producer she talked to said they needed increased or different irrigation.

"There's a huge pressure on already depleted water sources," she said.

"Even olives are needing to be irrigated.

I have an olive grower who harvested 90 per cent less than usual because there's not the right amount of rain."

But while irrigation was one of the solutions, Dr Crimp explained it came at a cost.

Aside from the infrastructure required, there was the cost of water, especially for those who did not have access to bore water.

"The rainfall we rely on to get a crop from a seedling to maturity [is not] sufficient," Dr Crimp said.

"So we are more reliant on irrigating crops, which increases the cost of growing things.

"Unless we have permanent water sources, it's not hugely sustainable."

Ice, ice baby

Chris Fowler holds some of his garlic bulbs, ready for market. ( ABC News: Kate Midena )

If the prolonged heat, dry soil and dumpings of rain were not enough for growers to deal with, unseasonable frosts were also destroying their crops.

"Managing heat stress and frost has become more of a challenge," Dr Crimp, who has conducted research into the impact of changing frost frequency, explained.

"There used to be clear windows where the frost would occur. Now we have heatwaves and frost events which are occurring and intersecting, which makes it difficult to sustain crops.

"You could get a frost in October and a heatwave in April."

Farmer Geoff Foster holds some just-picked fennel, grown in his greenhouse. ( ABC News: Kate Midena )

While changing frost frequency had already had an impact on wheat production nationally, locally, fruits like cherries and apples, which could usually be grown successfully during cold weather, were suffering.

"There are more extreme frosts, but less chilling time, and there needs to be that chill for the plants to fruit the following year," Ms Gaha-Morris said.

"We've had really good luck in the past with fruits like cherries and apples that need chilling time. But they are experiencing trouble because of the change in wintertime temperatures. They need weeks of frost, and they're not getting it.

"Every year the bar gets moved. We can't rely on what the weather's going to do anymore."

What about your own backyard?

Beetroot, almost ready to harvest at Geoff Foster's farm. ( ABC News: Kate Midena )

If even experienced farmers and community growers are having trouble with unpredictable weather patterns, what does that mean for the humble backyard gardener?

"I'd encourage people to keep a record of their temperature and rainfall and go back and review that regularly," Dr Crimp suggested.

"If you're seeing a trend in that information, respond to that trend by adjusting your planting next year.

"Look at the climate records you have for your region and have a look at what the trends are and modify accordingly."

Ms Gaha-Morris urged gardeners to concentrate on building soil fertility.

"The more fertile your soil is, the more water it's going to hold," she said.

"Also, make sure gardens are shaded, that they're caring for pollinators, and avoid pesticides that kill pollinators."

But Ms Gaha-Morris said, if growing your own produce was not a possibility, people should continue to shop locally to support farmers.

"Buy seasonal and local and build a relationship with them," Ms Gaha-Morris added.

"There is so much pressure and an increased workload during these extreme weather conditions, you can't help but come out of that psychologically damaged.

"People need to be aware of where their food is coming from and who is growing it. It's people who work really, really hard to do it."