Biochar in ornamental Horticulture and Landscape
MODULE 1 — B4C project introduction
Short introduction to biochar in horticulture and landscape
This learning unit introduces biochar as a carbon-rich material obtained from biomass and highlights its emerging role in ornamental horticulture and landscape management. It aims to familiarize learners with the basic concept of biochar and its relevance as a sustainable input, setting the foundation for understanding its agronomic and environmental functions. This unit introduces biochar as a functional material used in horticulture. Learners understand that biochar is produced from biomass residues and can be reused as a soil or substrate amendment. The course explains concretely how it fits into horticultural practices: improving substrate structure, water retention, and plant growth conditions. It also highlights that biochar is not a uniform product—its properties depend on its origin and production conditions
Context: B4C project and EU sustainability goals
This unit explains how biochar contributes to real policy challenges. For example, using biochar allows growers to comply with waste management regulations by valorising crop residues instead of burning or disposing of them. It also contributes to reducing greenhouse gas emissions through carbon sequestration and supports the transition towards a circular economy by turning waste into a resource.
Key questions: Why biochar? What challenges does it address?
Here, learners explore concrete sector challenges: soil degradation, nutrient losses, water stress, and increasing environmental constraints. The course explains how biochar can address these by improving water retention, limiting nutrient leaching, and enhancing soil biological activity. It also encourages critical thinking: biochar is not a miracle solution and must be used strategically depending on the context.
Reflect on your starting point
Take a moment to think about your current understanding of biochar.
- What do you think biochar is used for?
- Have you ever used or encountered biochar in your work or daily life?
- Which sector or field best describes your experience?
This short reflection will help you identify your starting point and connect the course content to your own professional context.
MODULE 2 — Biochar properties and potential
Definition of Biochar
Biochar is a stable carbon-rich material with long-term persistence in soil. It emphasizes the difference with compost or organic matter: biochar decomposes very slowly and mainly acts through its structure and chemistry rather than as a direct nutrient source.
Production Process (Pyrolysis)
The course explains how pyrolysis temperature and feedstock (wood, crop residues, manure) determine the final properties of biochar. For instance, low-temperature biochars can contain more nutrients, while high-temperature biochars tend to have higher porosity and surface area.
Key physical and chemical properties
This is a key unit where learners understand how biochar works:
- Physical properties: Its high porosity increases water retention and improves aeration, which benefits root development and seed germination.
- Chemical properties:
- Its typically alkaline pH can correct acidic soils and improve nutrient availability.
- Its mineral composition can supply nutrients depending on the feedstock.
- Compounds such as karrikins, produced during pyrolysis, can stimulate seed germination and early growth.
- Biological effects: Biochar creates favorable habitats for microorganisms (bacteria, mycorrhizae), enhancing soil biological activity and plant health.
The unit also clearly explains limitations: some biochars may contain phytotoxic compounds, so quality control is essential before use.
Link to circular economy and carbon sequestration
Learners understand concretely that biochar acts as a carbon sink, storing carbon in soils for long periods and contributing to climate mitigation. It also promotes circular economy approaches by transforming agricultural or green waste into a value-added product that can even be marketed (e.g. carbon credits).
MODULE 3 — Applications in ornamental horticulture
Use of biochar in seedling production
Seed germination is one of the most sensitive stages in plant production: and early seedling development. At this stage, water availability and aeration are critical. Biochar, thanks to its porous structure, acts like a sponge. It retains water while maintaining air-filled pores around the seed. This creates a more stable environment for germination.
When finely ground biochar is incorporated into a substrate, it helps keep moisture close to the seed, improving imbibition—the very first step of germination. At the same time, it prevents waterlogging, which can reduce oxygen availability and slow down emergence.
In some cases, biochar may also contain compounds that stimulate germination, such as karrikins—natural molecules formed during biomass combustion. These can trigger faster or more uniform germination in certain species. However, results can vary depending on the type of biochar and the crop. This is why testing and adapting the material is essential.
Use in pot cultivation (flower and tree nurseries)
Here, biochar is typically mixed into growing substrates. It can also be combined with compost or fertilizers or applied directly in planting holes.
Its main interest lies in improving substrate performance:
- It increases water retention, helping reduce irrigation frequency
- It improves structure and aeration, supporting root development
- It limits nutrient losses by reducing leaching
In practical terms, this means more efficient use of water and fertilizers—two key challenges in nursery production.
For growers, this can translate into better plant quality and potentially lower input costs. But again, the effect depends strongly on the type of biochar used and how it is incorporated.
Experimental results and benefits (substrates, water retention, nutrient management, synergies with bacteria)
Experimental results show that biochar can provide clear benefits in some situations—but not always.
For example, in trials on crops like lettuce, tomato, or basil, biochar sometimes improves plant growth and development. In other cases, no significant effect is observed.
However, even when growth is not directly increased, biochar often improves:
- water retention
- resistance to stress
This means that biochar may not always boost yield immediately, but it can make the production system more resilient and efficient.
Another key point is synergy: biochar often performs better when combined with compost or beneficial microorganisms.
The key message here is simple: biochar is not a universal solution. Its effectiveness depends on the production system, the crop, and how it is used.
Reflect on a Practical Situation
Imagine you are advising a nursery or plant producer who is considering using biochar.
Reflect on the following questions:
- In which production stage(s) do you think biochar could provide the greatest benefit (e.g. seed germination, pot cultivation, or another application)?
- What potential advantages would you expect?
- What factors would you want to consider before recommending its use?
There is no single correct answer. Use the information from this unit to justify your reflections and consider how the effectiveness of biochar depends on the production system and application.
MODULE 4 — Applications in landscape management (green spaces)
What is soil fertility – structure, nutrients, soil life…
In landscape management, improving soil fertility is often a major challenge—especially in urban environments.
Soil fertility is not just about nutrients. It includes three key dimensions:
- physical structure
- chemical composition
- biological activity
Compacted soils, poor organic matter content, and low biodiversity are common issues in urban and degraded soils.
Understanding these factors is essential before introducing any amendment—such as biochar
Biochar services in soils and green spaces
In this context, biochar provides several important ecosystem services.
First, it improves soil structure. Its porous particles help loosen compacted soils, making it easier for roots to grow.
Second, it increases water retention. This is particularly important in urban green spaces, where irrigation is often limited and drought stress is common.
Third, biochar supports soil life. Its structure offers a habitat for microorganisms such as bacteria and mycorrhizal fungi, which play a crucial role in plant nutrition and health.
Altogether, these effects contribute to more resilient and sustainable green spaces.
Focus on Biochar and soil decontamination (cadmium example)
In some cases, soils are not only poor—they are also contaminated.
Biochar has the ability to adsorb and immobilize certain pollutants, including heavy metals like cadmium.
This does not remove the contaminant, but it reduces its mobility and bioavailability, making the soil safer for plants and limiting transfer into the environment.
This makes biochar a promising tool for soil remediation in urban or degraded areas.
Urban and landscape uses of Biochar
Typical applications include:
- urban parks
- roadside plantings
- brownfield or degraded sites
In these environments, plants often face multiple stresses: poor soil, drought, compaction, or pollution.
By improving soil physical and biological conditions, biochar helps plants establish more easily and survive under these constraints.
It is particularly useful in low-maintenance systems, where long-term soil improvement is needed.
Examples of projects, successes and barriers
Real-world projects show that biochar can deliver strong benefits—but also reveal some limitations.
Success factors include:
- choosing the right type of biochar
- adapting application rates
- combining it with other amendments
However, barriers still exist:
- variability in product quality
- limited technical knowledge
- cost and supply constraints
This highlights the importance of a case-by-case approach. Biochar must be understood and adapted—not just applied blindly
Apply Your Knowledge
Think of a landscape management project you are currently working on—or imagine one of the following scenarios:
- An urban park
- A roadside planting
- A degraded or compacted site
Reflect on the following questions:
- What are the main challenges in this project (e.g. drought, poor soil, compaction, contamination)?
- How could biochar help address these challenges?
- What factors would you consider before deciding to use biochar?
Use the knowledge from this module to explain your reasoning. Remember that successful applications depend on the site conditions and the type of biochar used.
MODULE 5 — Closing Unit
How to integrate biochar into professional projects
This unit synthesizes the course by guiding learners through decision-making: choosing the right biochar, defining objectives (agronomic, environmental), and adapting application methods.
Introduction to B4C website and mapping tool (suppliers)
Learners are introduced to practical tools that help them identify suppliers and resources, facilitating real-world adoption.
Key takeaways
The unit reinforces core messages:
- biochar is a multifunctional tool, not a one-size-fits-all solution
- its effectiveness depends on properties, context, and application method
- it has strong potential for sustainability and climate mitigation
Plan Your Next Steps
Imagine you would like to introduce biochar into your own work or an organisation you are familiar with.
Reflect on the following questions:
- What would be your main objective for using biochar?
- Which factors would you consider when selecting a suitable biochar product?
- Where would you look for reliable suppliers or additional information?
- What would be your first step towards implementing biochar in practice?
You can explore the B4C map to identify potential suppliers or resources in your region.
This activity encourages you to translate the knowledge gained throughout the course into a realistic action plan.