When you are out and about at this time of year in many parts of Australia, a cold and sometimes drab winter is relieved by a blaze of brilliant yellow: soursob.
It can look pretty, but sadly it’s an introduced weed that should have nothing to do with an Australian winter.
Soursob, Oxalis pes-caprae, is an introduced weed from Africa. It is also known as soursop, sourgrass and Cape sorrel, among other names. The name pes-caprae means goat’s foot and refers to the pattern formed by the leaves.
Soursob was first planted in Australian gardens for its flowers. These days the very mention of it would strike fear into the hearts of most gardeners – once it’s there, it’s very hard to get rid of.
Edible but problematic
Many people will know soursob from childhood.
I remember, as a child, we would eat the stems of these bright yellow, five-petalled flowers with a clover-like leaf – the taste is sour but not unpleasant.
The plant is as popular with little ones now. Posies are easily gathered, stalks tasted and taken home as a trophy of the day’s walk or visit to a playground.
The sour taste is due to the significant quantities of oxalic acid in soursob. Oxalic acid (H?C?O?) is a small organic chemical that occurs naturally in humans as part of the metabolism of vitamin C and collagen.
It is found in many plants humans eat, including spinach, beans, potatoes and almonds. In other common foods such as rhubarb, peanuts and in a number of forage plants, oxalic acid adds flavour.
In its native South Africa, soursob has been widely used as a food or flavouring. A childhood dab on the tongue and the sour taste will do no harm, but taking things to excess can be problematic. The consumption of soursob in large amounts has been reported as a cause of death in hungry sheep.
Given soursob can occur in great swards (meadows) in rural areas and is a very difficult garden pest to control, getting rid of it must be a priority.
But this is an Oxalis species we’re dealing with; getting rid of it is much easier said than done.
Soursob spreads by bulbs and the smaller bulbils (tiny bulbs that crowd around the main, larger bulb).
In its native South Africa the plant also seeds, but rarely does so in Australia because the introduced plants are usually infertile. This means the weed spreads more by bulbs and bulbils than by seed. We have dodged a bullet there, perhaps by sheer good luck.
On a large scale and in rural situations the only current way to effectively deal with soursob is to use herbicide or out-compete it with pasture or another crop that shades it out.
You cannot plough or cultivate the soil as this spreads the bulbs and bulbils. Whether you use herbicide or not, eradication will take several years and demands immense patience.
In home gardens, where many people are wisely reluctant to use chemicals, there are alternatives – but nearly all require an almost inhuman persistence.
The best time for control is just before flowering (early to mid-winter) when the bulbs are depleted and have put their resources into leaves and flower stalks and buds (sometimes called bulb exhaustion).
The idea is to starve the bulbs and bulbils over time. There are several approaches:
don’t pull the plant out as this just spreads bulbils
instead, simply remove all the leaves and flower buds and stalks; it’s not difficult to do by hand – but you have to keep doing it
mow over soursob in your lawn – but you have to keep doing it
plant over the soursob in an attempt to shade it out, which again can starve the bulbs – but you have to keep doing it
attempt to smother and starve the plants with cardboard, carpet or plastic, but this is not good for your soils – and you have to keep doing it (I don’t recommend it).
All of these approaches take lots of time, effort and persistence. Adding a good layer of mulch (75-100mm deep) makes control and ultimate eradication much easier.
When it comes to a battle of persistence between a weed and a human, the weed will win most of the time. That is one of the things that makes a weed a weed.
Soursob is a persistent curse, but it can be beaten. It may take a few years, but in a garden I can attest that control and starvation does work.
What a sense of achievement – or is it victory? – you get when the dense swathe is diminished and then finally vanquished.
Gregory Moore does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Australian homes and cities are increasingly producing and storing their own power.
After two decades of growth, solar panels are now on the rooftops of one in three Australian homes. And home batteries have surged after the Australian government began offering subsidies last year. Around 450,000 batteries had been installed by the end of 2025 – about 4% of Australia’s 10.9 million households.
What would happen if these trends continue? It’s tempting to picture a future where Australian homes and cities could power themselves using these two decentralised technologies.
But while rooftop solar and batteries can take us a long way, they aren’t enough to take most households off-grid – let alone run entire cities.
The real question is how much household power demand can be met by solar and batteries, at what times of day, and under what conditions. These five charts show what’s possible – and what’s not.
How far could these technologies take us?
As of April 30, the National Energy Market had close to 26 gigawatts installed capacity of small-scale rooftop solar, which includes small-scale rooftop PV installed on homes, businesses and other eligible premises.
Solar panels never produce at their full capacity. Clouds cut output, and there’s no sun at night. As a result, that 26GW of panels produced 4GW of power on average from January to March this year.
That’s still significant. It’s equivalent to 16% of demand, and almost four times higher than the same quarter eight years ago. Solar-rich South Australia had 28% of underlying demand met by rooftop solar. During sunny, low-demand periods, rooftop solar can meet around 60% of National Energy Market demand.
Rooftop solar capacity has been increasing rapidly since 2017. But it could go much higher still. Australia’s energy market operator (AEMO) projects small-scale solar capacity (rooftop and other small systems) could almost triple by 2050 to around 87GW.
If all suitable household rooftops were fully used for solar, capacity could reach around 61GW. But homes are only part of Australia’s rooftop solar potential. Once commercial, industrial and other buildings are included, the technical potential is much larger – around 179GW.
This also helps explain why AEMO forecasts for small-scale solar capacity eventually rises above 61GW – its forecast includes rooftop and other small-scale systems on businesses and other premises as well as homes. When large-scale solar farms are also counted, Australia is likely to pass 61GW of total solar capacity within a decade.
This progress is significant. But it also changes the problem that the grid must solve.
Before the rise of wind, solar and batteries, coal plants supplied much of Australia’s electricity. These work best when running steadily, as they can increase or decrease output relatively slowly.
Solar changes this equation.
Power from rooftop solar first meets demand within homes and businesses. At times, solar can exceed local demand, requiring excess power to be exported to the grid, stored or curtailed. As the sun sets, solar output falls rapidly. Demand for grid-supplied electricity then rises sharply, often peaking in late afternoon or evening.
This pattern of low daytime demand and high evening demand is known as the “duck curve”. It poses challenges for grid operators, who have to manage very low grid demand during the day and then rapidly bring on other generation or storage as solar output falls and evening demand rises.
The problem can be partly solved by coordinating home batteries and other types of energy storage, as they can store excess solar and release it at peak times.
What rooftop solar and home batteries can’t do
While rooftop solar and home batteries have clear promise, they’re not a simple substitute for the grid, especially during evenings, heatwaves or prolonged cloudy periods.
Heavy industry, data centres and other big power users require substantial and often continuous supplies of electricity which cannot be wholly met by small-scale energy production.
Home batteries are already reducing how much power households buy from the grid.
But their usable stored energy remains limited relative to the amount of rooftop solar generation available. They’re good at reducing how much expensive power households buy at peak times, but not so good at providing extended backup over an extended cloudy period or during evenings amid an intense heatwave.
What future should we aim for?
What we’re likely to see is rooftop solar and household batteries operating alongside large-scale solar and wind farms to supply much of Australia’s electricity as conditions allow.
We will still need local networks to supply electricity when solar output is low, and carry surplus power in the opposite direction. New transmission lines are needed to better connect large scale renewable areas with cities and heavy industry.
Long-duration energy storage, such as pumped hydro and grid-scale batteries, will be necessary to keep Australia running through periods of low wind and sunlight. A few gas plants will have to be kept as backup.
As the renewable transition progresses, we will need to judge progress not by how many solar arrays and home batteries have been installed, but by how well we can make use of them alongside larger-scale renewables and storage.
We should not aim for a future where household after household quits the grid. Far better to build a resilient, integrated system where homes produce and store more electricity, power grids deal with two-way flows of power intelligently and large-scale renewables and storage cover the periods rooftop solar and batteries can’t respond to.
Magnus Söderberg does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
What flashes to mind when you hear the word “whiplash”?
Perhaps you picture someone’s head rocking back and forth during a car crash – a jarring and often painful experience. Climate whiplash is no different.
Our climate is rapidly warming, dramatically reshaping weather around the globe. In this three-part series, we explore a range of emerging climate phenomena and consider how to respond to their destructive effects.
Not just buzzwords
In general, the term weather whiplash refers to abrupt weather changes that happen on a daily to weekly scale. For example, a downpour may immediately follow a heatwave, or temperatures could be freezing one day and baking hot the next.
At the start of 2026, the Otways region in southern Victoria experienced weather whiplash. In the space of two weeks, a huge bushfire gave way to a record-breaking flood and then an historic heatwave.
Climate whiplash is sometimes used to describe these rapid shifts. However, because climate relates to the long-term average of weather, climate whiplash more accurately describes changes on a monthly to annual scale. Another term scientists use is “climate volatility”.
The current drought afflicting the United Kingdom is a prime example of climate whiplash. After an unusually wet start to the year, parts of the UK endured their driest July on record, with farmers struggling to keep their crops and pastures alive.
Researchers and emergency responders are increasingly concerned by “compound disasters”, which include whiplash events. These occur when multiple kinds of extreme weather collide, and can happen at the same place and time or back-to-back. This compounding makes the events much more destructive than any single disaster.
In Australia, we are all too familiar with both climate and weather whiplash.
From year to year, our rainfall can swing violently between soaking wet and alarmingly dry. In fact, Australia’s precipitation patterns are among the most variable on Earth. This is largely due to temperature seesaws in the nearby Indian and Pacific Oceans that affect weather patterns and moisture availability over Australia.
Parts of Australia are also known for their temperamental temperatures. Melbourne, for example, is famous for cycling through four seasons in one day. This happens most often when hot air from Australia’s arid centre is shoved out of the way by cold air from Antarctica. This air-mass replacement leads to remarkable drops in temperature, otherwise known as a cool change.
Overseas, the United States and continental Europe are other whiplash hotspots, particularly for rapid temperature changes. In these parts of the northern hemisphere, the jet stream that keeps polar air up near the Arctic can wiggle and weaken, allowing freezing temperatures to spill out onto temperate regions.
What’s more, computer simulations reveal these trends will only worsen if we keep heating the planet by adding more greenhouse gases into the atmosphere. A major reason for this is climatic extremes are more dramatic than they were when our planet was cooler. Heatwaves are hotter, heavy rainfall is heavier and droughts are even drier.
Research suggests a warming planet is altering the speed and behaviour of the weather systems that drive these extremes. For example, the polar regions are warming faster than the tropics, particularly in the northern hemisphere. This uneven warming reduces the temperature change between the equator and the poles, which in turn weakens large-scale wind and pressure patterns that are driven by these temperature differences.
Rapidly changing weather places immense strain on our communities, ecosystems and emergency services.
Quick shifts between hot and cold temperatures affect human health and whole economies. Dramatic shifts between wet and dry conditions have been found to damage soil health, increase water contamination and fuel fast-moving bush and wildfires.
The phrases weather and climate whiplash give scientists another way to communicate just how extreme our weather is becoming. They also enable emergency responders and health services to better plan for back-to-back extremes, and communicate with vulnerable communities.
Weather and climate whiplash may sound like buzzwords. But these terms are a visceral expression of a worrying reality: the more we keep burning coal, oil and gas, the more chaotic and dramatic our weather will become.
Many of Australia’s floral species have evolved over millions of years alongside fire, but are bushfires becoming too frequent for some flowers to survive?
Prediction comes amid warning of ‘extreme heat’ this week with temperatures of 38C possible
The Guardian’s environment editor, Fiona Harvey, has written a useful explainer about the UK public services that are struggling in the extreme weather. You can read it in full here:
There’s only one solution in the end to the drought now declared across most of England and that’s rain, says Hannah Cloke, professor of hydrology at the University of Reading.
An important consequence of drought is that very dry soils can become less able to absorb rainfall when it does arrive. This can increase surface runoff and can even contribute to localised flash flooding, particularly if rain falls intensely over a short period.
The current situation highlights the need to improve long-term resilience to both drought and flood risk as climate variability increases, and shows one more damaging impact of the burning of fossil fuels.
