However, soil is often contaminated with chemicals, invasive plant species, seeds, roots, and plant pathogens. If this soil is reused without proper treatment, it can unintentionally spread invasive species to new areas.

Two technologies are sometimes mentioned when treating contaminated soil: soil washing and SoilSteaming.

While both methods process soil, they serve very different purposes — and only one of them is effective when dealing with biological contamination such as invasive plant seeds and plant pests.

What is Soil Washing?

Soil washing is a remediation technology designed to remove chemical contamination from soil.

It is commonly used to treat soil polluted with:

• heavy metals
• petroleum hydrocarbons
• industrial pollutants
• contaminated fine particles

The process separates soil into different particle sizes and washes the soil with water and sometimes chemical additives. Many contaminants bind to the smallest soil particles (silt and clay), which are separated from the larger mineral fractions.

Typical soil washing steps include:

1. Excavation of contaminated soil
2. Screening and separation of soil fractions
3. Washing with water or chemical solutions
4. Separation of contaminated fines from reusable soil

The cleaned mineral fraction can then be reused in construction projects.

Why Soil Washing Does Not Work for Invasive Species

While soil washing can remove chemical contaminants, it is not designed to eliminate living organisms.

When soil contains biological contamination such as invasive plants or plant pathogens, several problems occur.

Seeds survive the washing process

Many invasive plants produce extremely resilient seeds that can survive:

• water exposure
• mechanical disturbance
• transport through treatment systems

These seeds can easily follow the soil through the washing process and remain viable afterward.

Roots and plant fragments can regenerate

Some invasive plants spread through root fragments or rhizomes. Even small pieces can regenerate and grow into new plants if they are not destroyed.

Soil washing may break the soil apart but does not reliably destroy plant material.

Risk of spreading invasive species

Because seeds and plant fragments can survive the process, soil washing may unintentionally spread invasive species rather than eliminate them.

For this reason, soil washing is generally not considered a reliable treatment method for soil contaminated with invasive plants or biological pests.

What is SoilSteaming?

SoilSteaming is a thermal soil treatment method that disinfects soil using heat.

Instead of separating contaminants from the soil, steam is used to raise the soil temperature to above 90°C.

At these temperatures, biological organisms cannot survive.

Soil steaming effectively eliminates:

• invasive plant seeds
• roots and rhizomes
• fungi
• bacteria
• nematodes
• insects and larvae
• soil-borne plant pathogens

The method has been widely used in horticulture, greenhouses, and plant nurseries to disinfect growing media and soil before planting.

How Heat Destroys Seeds and Plant Pathogens

Living organisms rely on proteins and cell structures that break down when exposed to high temperatures.

When soil temperatures exceed approximately 70–90°C, critical biological functions fail.

At these temperatures:

• seed viability is destroyed
• root tissue breaks down
• pathogens are inactivated

Unlike soil washing, which attempts to separate contaminants, soil steaming treats the entire soil volume.

This ensures that invasive species and plant pathogens are eliminated rather than redistributed.

SoilSteaming vs Soil Washing – Key Differences

Why Thermal Soil Treatment is Important for Invasive Species Control

The spread of invasive plants through soil transport is a growing challenge worldwide. Construction activities, infrastructure projects, and land development often move large volumes of soil between locations.

If soil containing invasive seeds or plant fragments is reused without proper treatment, new infestations can occur.

Effective soil treatment therefore requires technologies that destroy biological contamination rather than simply separating it.

Thermal soil treatment, such as SoilSteaming, provides a reliable way to eliminate invasive plant seeds, roots, and pathogens before soil is reused.

Soil washing and SoilSteaming are two very different soil treatment technologies.

• Soil washing is effective for removing chemical contaminants but does not destroy biological organisms.
• SoilSteaming disinfects soil using heat and eliminates invasive plant seeds, roots, and plant pathogens.

When soil is contaminated with invasive species or biological pests, SoilSteaming provides a far more reliable solution for safe soil reuse.

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Incorrect handling of soil can lead to project delays, increased costs, regulatory non-compliance and long-term environmental damage.

The good news is that much of this risk can be eliminated before the first shovel hits the ground – if the right decisions are made early.

Below are the key steps every project should follow.

1. Identify invasive species before the design phase begins

The first – and most important – step is to understand what is present on site.

• Carry out an early ecological / environmental survey
• Identify:
  • invasive plant species
  • areas at risk of spread
  • existing soil that may be contaminated with seeds, roots or plant material

👉 Projects that overlook this in the early phase often experience:

• sudden stoppages on site
• costly emergency measures (often dig & dump)

2. Understand that soil is biological material – not just bulk mass

Soil containing invasive species is not inert waste – it is a biological risk material.

Common mistakes include:

• temporary storage without containment
• transporting soil between multiple locations
• reusing soil without treatment

The result can be unintentional spread both within and beyond the project area, often not discovered until months or even years later.

3. Plan soil management as part of the overall project logistics

Soil should be treated as a dedicated workstream, just like concrete, steel or logistics.

Well-managed projects:

• clearly define which soils are “clean” and which are “risk material”
• establish clear procedures for:
  • excavation
  • temporary storage
  • treatment or final use
• avoid unnecessary transport and re-handling

👉 This leads to better control, lower costs and fewer surprises.

4. Avoid “dig & dump” as the default solution

Excavating soil and sending it to landfill has long been the standard response to invasive species. In practice, this approach is often:

• expensive
• logistics-intensive
• dependent on limited landfill capacity
• environmentally unsustainable

Across many parts of Europe, millions of tonnes of biologically contaminated soil are handled this way every year – despite the soil itself often being of high quality.

5. Consider treating soil on or near the construction site

Modern projects increasingly view soil treatment as an alternative to landfill.

Key benefits include:

• reduced transport and disposal costs
• elimination of spread risk
• enabling safe reuse of soil within the project
• improved documentation and control

For many projects, this can be the difference between a reactive and a proactive environmental approach.

6. Document – for authorities, clients and future liability

Regardless of the method used, documentation is critical:

• What was identified?
• How was the soil handled?
• How was biological risk eliminated?

This protects:

• the contractor
• the client
• the developer

— both legally and financially.

Final thoughts: Start right to avoid costly consequences later

The spread of invasive species is rarely the result of bad intent – but often of insufficient planning in the early stages.

The most successful projects:

• take biological risk seriously
• plan soil management strategically
• choose solutions that reduce both environmental impact and cost

At SoilSteam, we work with contractors and developers who want to:

• eliminate biological risk in soil
• reduce reliance on landfill
• enable safe reuse of soil

👉 Engage early in the project phase – that’s where the best solutions are created.

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2025 has been a year in which SoilSteam clearly moved from being a “promising technology” to a documented solution in real-world applications. We have experienced strong international interest, several important projects – and, not least, a clear direction: soil as a resource, not waste.

This was not just a demo – it marked that the market is now moving rapidly toward more circular solutions for soil management.

First major step in Sweden: EWGroup

In 2025, we took an important step into the Swedish market through our collaboration with EWGroup, which became the first operator in Sweden to implement the SoilSaver 20 at its facility in Flen. This marks the beginning of a broader commitment in the Swedish market, where the need for circular handling of soil masses and control of invasive species is growing rapidly.

Trafikverket and Svevia tested SoilSaver in a project in Umeå, Sweden

SoilSteam then entered into an agreement with Svevia and Trafikverket for the treatment and recovery of approximately 1,500 tonnes of soil masses infested with lupins in Umeå. The project was planned for completion during May–June 2025 and was described as SoilSteam’s first collaboration with Trafikverket in Sweden.

This sends a strong signal that our method addresses a growing need in European infrastructure projects: stopping the spread of invasive alien species while simultaneously reducing landfilling.

An international meeting place: SoilSteam Demo Day 2025

In the autumn of 2025, we gathered more than 200 participants from eight nations at Gjennestad in Vestfold for SoilSteam Demo Day. The event demonstrated how thermal treatment can transform contaminated or infested soil and peat into a valuable resource, both for construction projects and for greenhouse production.

Gavin Griffiths Group – Japanese knotweed and the first UK unit

In the UK, 2025 has been a breakthrough year. Together with the Gavin Griffiths Group, we have taken important steps to document effectiveness against Japanese knotweed. This work is linked to the launch of what has been described as the UK’s first steam treatment unit for soil at their facility in the summer of 2025.

This marks the beginning of a broader UK journey, where documentation and strong partnerships are central.

Our goal is to save as much soil as possible from being landfilled. During 2025, our fantastic customers used their SoilSaver machines to save more than 23,000 tonnes of soil from disposal. This took place in Norway, Sweden, and the UK. Without SoilSavers in the contracting industry, this would never have been possible. A huge thank you to everyone who made this happen 😊

Professional documentation and international relevance: Sardinia Symposium 2025

In September 2025, we also participated in the Sardinia Symposium, where we demonstrated how SoilSteam technology is already being used in practice across multiple segments – from road and construction projects to the reuse of growing media in greenhouse production.

For many, this comes down to a fundamental question: Is it possible to control pests and invasive species without destroying soil quality? Our experience and documentation clearly show that the answer is yes.

New applications: substrates and growing media

2025 has also been about growing media and circularity in greenhouse production. SoilSteam has published several articles on the reuse of substrates and how this can contribute to more sustainable production.

In the summer of 2025, we carried out our first research project documenting that peat and substrate products can be treated using our SoilSaver technology and reused instead of being replaced with new material. This represents a new way of thinking about circularity in international greenhouse production and will also lead to significant reductions in methane and CO₂ emissions.

New customers and new continents

The end of 2025 was intense. We held meetings with several stakeholders in greenhouse production, waste management, and the contracting industry across multiple countries. This resulted in several SoilSaver units being sold for delivery next year during the final months of 2025.

One of these units will be delivered to North America, becoming SoilSteam’s first machine operating outside Europe. This is a major milestone for SoilSteam.

What do we take with us into 2026?

2025 showed us three things very clearly:

1. The need for circular soil management is growing rapidly – across multiple industries at the same time.
2. SoilSteam is moving from “pilot” to “scalable practice.”
3. We have documented that soil steaming works – and people understand it. During 2025, we were contacted by more than 200 companies from 24 countries interested in SoilSteaming. We believe this strong interest will grow even further in 2026.

Thank you to our customers, partners, and everyone who met us in 2025 – we look forward to building further in 2026.
Merry Christmas and Happy New Year!

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This represents an important milestone for us – not only because we now have documented results from the UK, but also because we are working alongside one of the country’s leading experts in the field.

The background is a long-standing challenge faced by UK authorities:

• The spread of invasive species threatens nature and infrastructure
• Enormous volumes of soil are being sent to landfills instead of being reused

With SoilSteam SoilSaver, we have now demonstrated that there is a safe and effective way to address both of these issues at the same time. Together with Dr. Jones and other leading UK experts, we will continue to build evidence showing that SoilSteam can be a key part of the solution for these pressing challenges.

This is just the beginning of our journey in the UK – and we look forward to sharing more soon.

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For SoilSteam, this was an opportunity to demonstrate how steam-based soil remediation is now moving from experimental stage to industrial reality.

From Theory to Practice

For many years, the key question has been: Is it really possible to clean soil infested with invasive species and pathogens while preserving its natural qualities?
Our answer is a clear yes – and at Sardinia Symposium, we were able to show how SoilSteam technology is already being applied in practice, from landscaping and horticulture to full-scale agricultural operations.

Through controlled steam treatment, we restore a healthy microbiological balance in the soil – without the use of pesticides or chemicals.
The result is clean soil, ready for new growth, in a way that is both scalable and economically sustainable.

Research, Collaboration and Global Solutions

A central theme at this year’s conference was the need for circular and regenerative approaches in the global food system.
In our presentation, SoilSteam highlighted our collaborations with leading research institutions – which sparked great interest among both academics and industry professionals.

Our field data from large-scale commercial projects were particularly noted as an example of how technology can bridge the gap between research and real-world implementation.

A Global Commitment

SoilSteam received numerous inquiries from international stakeholders eager to understand how steam technology can be integrated into existing soil management systems.
It is clear that the challenges we are addressing – soil degradation, pollution, and unnecessary landfill disposal – are shared across borders.

The Road Ahead

Our participation at Sardinia Symposium marked not only a professional milestone, but also another step in SoilSteam’s mission to make sustainable soil recovery accessible to more people and industries.
Through continued research, strong partnerships, and by deploying our machines in an increasing number of countries, we aim to build technology that protects one of our most vital resources – the soil itself.

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Lindum, in collaboration with SoilSteam, has carried out an exciting trial to combat the highly invasive plant Bohemian Knotweed. Using SoilSteam’s SoilSaver 20 machine, soil masses containing knotweed rhizomes were treated with steam at 70 °C for 12–16 minutes.

The results are very promising:

• Control samples (without steam) produced up to 13 new shoots.
• The steam-treated samples showed no regrowth at all.

This demonstrates that steam can be an effective and environmentally friendly alternative to chemical control methods. The trial confirms that treatment at 70 °C is sufficient to prevent further spread of Knotweed, a plant notoriously difficult to eradicate.

The report concludes that steam treatment has significant potential as a tool in the fight against invasive alien species. For Lindum and SoilSteam, this marks an important step toward finding sustainable solutions for both nature and society.

👉 Read the full report here:

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Soil – A Vital, Non-Renewable Resource

The day opened with Vestfold County Mayor, Anne Strømøy, who reminded the audience that soil is one of our most important – yet non-renewable – resources. She announced that the county will now require contractors to recycle soil masses containing invasive species and plant pathogens instead of treating them as waste.

“We cannot continue to treat soil as a waste problem. It must be seen as a resource to be protected and reused,” said Strømøy.

Technology That Changes the Industry

SoilSteam CSO, Hans Kristian Westrum, emphasized that landfilling soil has no place in a modern, sustainable society.

“SoilSteaming is often more affordable than landfilling. The technology removes weeds and plant pathogens while improving soil quality. With three machines already in Norway, one in Sweden, and one in the UK – the solution is here. Now we call on municipalities, consultants, and contractors to make SoilSteaming the standard in construction and road projects.”

The audience also heard from Gjennestad Drift’s Arne-Olav Klevsgård, who shared why his company is now adopting SoilSteaming:

“We’ve long struggled to secure soil of good quality. Now we can guarantee weed-free soil for ourselves and others, while contributing to a more sustainable resource cycle.”

From Theory to Practice

After the presentations, participants witnessed SoilSteam’s machines in action. Two models – SoilSaver 20 and SoilSaver 5 – were demonstrated in the field. Visitors also compared steamed soil with untreated soil, six weeks after treatment. The results were striking:

The steamed soil remained completely weed-free

• Grass grew better in the treated soil than in the untreated sample

“SoilSteaming doesn’t just eliminate weeds and pathogens – it can actually improve the soil’s growth properties,” summarized SoilSteam CEO, Ken Roar Riis.

A Step Toward a Circular Future

The Demo Day made it clear that interest in delivering heat-treated soil in line with the new upcoming standard is growing fast. With support from public authorities, industry leaders, and pioneering companies, SoilSteaming is becoming a key driver for a circular economy in both construction and agriculture.

You can see a summary of the day here

✅ Learn more about SoilSteam and our mission to redefine soil management: www.soilsteam.com

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Soil recovery as an alternative to costly landfilling

Instead of transporting the soil to landfill – which is both expensive and environmentally taxing – the masses were treated directly on site using heat. The SoilSaver technology uses hot water vapor to eliminate biological contaminants, without chemicals, while preserving the soil’s structure and function as a growing medium.

The project was carried out as planned in terms of time and budget. Trafikverket views the technology as a potential way to reduce the high costs associated with current practices:

“This is about finding out whether we can handle the soil on site at a reasonable cost instead of hauling it away and burying it in landfill, which is expensive,” says Claes Dahlgren, national coordinator for invasive species at Trafikverket.

“The landfill cost alone is around 1,500 SEK per ton,” he adds.

– Landfilling costs several times more than treatment

Hans Kristian Westrum from SoilSteam comments:

“We see time and again that recovering soil with our SoilSaver makes projects more sustainable – not only environmentally and ecologically, but also economically.
Our treatment cost is just a few hundred NOK per ton. In this project, the landfill cost alone was several times higher than the treatment cost.

We have to stop landfilling material that is cheap and easy to recover. Landfills should be reserved for waste we cannot recycle – not for valuable resources that can be reused with minimal effort,” Westrum concludes.

Next steps

Trafikverket will follow up the project throughout the summer and fall to assess the results. Key questions include whether the lupins are effectively eliminated – and whether the treated soil remains suitable for grass and plant growth.

SoilSteam looks forward to the outcome and hopes the SoilSaver can become a useful tool in Sweden’s efforts to manage invasive species through circular, cost-effective and environmentally responsible practices.

Read more from Trafikverket here:
New method tested to stop the spread of invasive plants – Trafikverket (in Swedish)

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The initiative was carried out by Dokka Entreprenør in partnership with SoilSteam, a company based in Sandefjord. With SoilSteam’s custom-built machine, the SoilSaver 20, over 4,000 tonnes of soil were treated on-site – soil that otherwise would have been trucked to a landfill due to contamination by species such as Japanese knotweed and Canadian goldenrod.

A New Approach to Sustainable Soil Management

The project was a pilot, and a crucial step toward more sustainable practices in large-scale construction. According to Mari Skybak of the Norwegian Public Roads Administration, the bidding process encouraged contractors to propose innovative solutions – and DEAS, the executing contractor, was the only one to suggest soil steaming as an alternative to landfill disposal.

“We have a strong focus on biodiversity and a vision of zero net loss of nature in our sustainability strategy,” says Skybak. “The idea of steaming the soil instead of disposing of it allowed us to reuse a limited resource – topsoil – right on site. That’s a win for both the environment and the budget.”

Contaminated soil is not only a biological problem – it’s also a resource issue. Topsoil is non-renewable on human timescales. Disposing of it due to invasive species results in a loss of valuable natural material. Steaming the soil and reusing it drastically reduces transportation, emissions, and the strain on landfill capacity.

Encouraging Results Across the Board

Despite some logistical challenges – including heavy rain and clay-rich soil – the project went ahead as planned. After steaming, the soil was returned to the site, seeded, and fertilized. The results? Strong vegetation growth, minimal weed presence, and no visible resurgence of invasive species so far.

“The grass has taken root quickly and grown well. With proper maintenance going forward, we’re optimistic,” says Skybak.

Hans Kristian Westrum, founder and Sales Director at SoilSteam, is thrilled with the outcome:

“This was the first time our technology was used in a live infrastructure project. We’ve now proven that the method is not only environmentally sound, but also cost-competitive. Plants grow just as well – if not better – in steamed soil, and there are no signs of the invasive species returning. That’s exactly what we aimed for.”

A Solution Gaining Traction

The success in Jevnaker is already spreading. According to Westrum, Sweden’s Transport Administration (Trafikverket) as well as several municipalities and county authorities in Norway are now encouraging – or even requiring – soil steaming as an alternative to landfilling contaminated soil.

“It’s incredibly important for us that large public agencies like the Norwegian Roads Administration take the lead. Their validation helps open doors. We expect to help recover over 100,000 tonnes of soil from being landfilled this year alone.”

Looking Ahead

Skybak is clear that the method won’t be a one-size-fits-all solution. It requires space, coordination, and the right project conditions. But when applicable, it offers clear environmental benefits.

“If a project has the space for soil storage and there’s a will to look beyond just the spreadsheets and carbon accounting, then steaming and reusing topsoil is the best way to protect a vulnerable natural resource,” she says. “I will definitely advocate for it in future projects.”

Rethinking Construction: Not Just Building, But Preserving

While many green innovations require major investment and long-term planning, the Jevnaker project shows how practical, implementable technologies can deliver immediate and measurable results. Perhaps the construction projects of the future won’t just be about what we build – but also about how we care for what’s already in the ground.

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