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Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems

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A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Horticultural Science and Ornamental Plants".

Deadline for manuscript submissions: closed (31 December 2025) | Viewed by 27711

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Special Issue Editors

Prof. Dr. Wanlai Zhou

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Institute of Urban Agriculture, Chinese Academy of Agricultural Sciences, Chengdu 610213, China
Interests: organic cultivation substrates based on plant-derived waste materials; the growth performance of horticultural crops in these substrates
Special Issues, Collections and Topics in MDPI journals

Dr. Wei Lin

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Institute of Urban Agriculture, Chinese Academy of Agricultural Sciences, Chengdu 610213, China
Interests: urban waste; compost; growing media; greenhouse gases; nitrogen cycle; soil microbiome
Special Issues, Collections and Topics in MDPI journals

Dr. Hong Wang

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Guest Editor

Institute of Urban Agriculture, Chinese Academy of Agricultural Sciences, Chengdu 610213, China
Interests: urban waste; microbial agent; Nitrogen transformation; fertilizer

Special Issue Information

Dear Colleagues,

Researchers have been exploring new materials and formulations for soilless cultivation substrates to enhance plant growth and nutrient uptake. One promising development is the use of biochar as a substrate, which has been shown to improve water retention, nutrient availability, and microbial activity in the root zone. Furthermore, because of the environmental concerns associated with peat extraction, our special issue aims to highlight innovative methods and technologies for developing sustainable alternatives to peat substrates. From biodegradable foams crafted from natural materials to organic substrates derived from agricultural waste, there is a growing interest in exploring eco-friendly substitutes that can reduce the horticultural industry’s reliance on peat-based substrates.

Advances in nutrient delivery systems, such as aeroponics and drip irrigation, have enabled more precise control over nutrient uptake and distribution in soilless cultivation systems. These systems allow for efficient nutrient delivery directly to plant roots, leading to improved growth rates and higher yields. The integration of technology, such as sensors, automation, and data analytics, has played a key role in advancing soilless cultivation practices. These technologies enable real-time monitoring of plant health, environmental conditions, and nutrient levels, thereby allowing growers to make data-driven decisions to optimize plant growth and resource efficiency. In addition, substrates from specific sources, such as plant material substrates rich in plant fibers, may have unique effects on crops, such as nitrogen fixation and phytotoxicity. Therefore, studying the performance of horticultural crops in different growing media and optimizing cultivation management practices accordingly is crucial.

By continuing to explore new materials, optimize nutrient delivery systems, and elucidate the interaction between soilless cultivation substrates and plants, the research progress in soilless cultivation substrates will lead to the development of innovative solutions that have the potential to revolutionize modern agriculture.

Prof. Dr. Wanlai Zhou
Dr. Wei Lin
Dr. Hong Wang
Guest Editors

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Keywords

soilless cultivation
growing media
biochar
biodegradable foam
agricultural waste
nutrient delivery systems
horticultural plants
nitrogen fixation
phytotoxicity

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Published Papers (13 papers)

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Editorial

Jump to: Research, Review

4 pages, 156 KB

Open AccessEditorial

From Waste to Resource: Driving Sustainability Through Eco-Friendly Substrates for Soilless Culture

by Wanlai Zhou, Wei Lin and Hong Wang

Plants 2026, 15(10), 1459; https://doi.org/10.3390/plants15101459 - 11 May 2026

Viewed by 118

Abstract

From high-tech greenhouses to urban vertical farms, the rapid global expansion of soilless cultivation has brought about unprecedented growing efficiency [...] Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

Research

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21 pages, 4107 KB

Open AccessArticle

Using Recycled Construction Waste Amended with Pine Bark as a Substrate for Urban Plantings

by Claire Kenefick, Stephen J. Livesley, John P. Rayner and Claire Farrell

Plants 2026, 15(3), 403; https://doi.org/10.3390/plants15030403 - 28 Jan 2026

Cited by 1 | Viewed by 796

Abstract

In urban plantings, mined sand and scoria are commonly used as low-nutrient substrates to improve plant establishment and growth. However, reliance on mined materials conflicts with sustainability policies promoting resource circularity and waste reuse. Construction wastes are readily available, and while their high alkalinity and density may limit plant growth, incorporating organic matter, like pine bark, can ameliorate these issues. We investigated whether construction waste amended with pine bark can support plant growth. We evaluated physical and chemical properties of 12 substrates combining four mineral components—scoria (mined), sand (recycled), crushed concrete (recycled), and crushed rock (recycled)—with pine bark (10%, 20%, and 50% v/v). We then tested eight of these substrates in a container experiment, evaluating the growth of two woody shrubs: Alyogyne huegelii and Goodenia ovata. All mineral components were alkaline (pH 9.2–12.3), with crushed concrete remaining hyper-alkaline despite pine bark addition. Greater pine bark volumes improved air-filled porosity but reduced water retention. Substrates with 50% v/v pine bark had lower plant biomass compared to those with 10% v/v. However, plant biomass was similar across all mineral components. This demonstrates that construction waste–pine bark substrates can support plant growth in urban plantings, supporting broader sustainability goals in cities. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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34 pages, 4505 KB

Open AccessArticle

Partial Replacement of Peat: Effects on Substrate Physico-Hydrological Properties and Sage Growth

by Anna Elisa Sdao, Sonia Cacini, Danilo Loconsole, Giulia Conversa, Giuseppe Cristiano, Antonio Elia and Barbara De Lucia

Plants 2025, 14(17), 2801; https://doi.org/10.3390/plants14172801 - 7 Sep 2025

Cited by 5 | Viewed by 2028

Abstract

The transformation of organic by-products derived from waste into value-added resources represents a promising strategy to advance circular economy principles and bolster environmental and agricultural sustainability, especially in soilless cultivation. This study evaluates the viability of three organic by-products—wood fiber (WF), coffee silverskin (CS), and brewer’s spent grains (BSGs)—as partial peat replacements in horticultural substrates. Ten growing media formulations were assessed, incorporating increased doses (0–40% v/v as peat replacement-PR) of each alternative by-product. The effects on physical and hydraulic substrate properties, along with plant growth traits, were examined using two ornamental Salvia genotypes, ‘Victoria’ and ‘Amistad’. To synthesize the multivariate growth data into a single, biologically meaningful metric, based on the first principal component, a Growth Index (GI), a PC1-derived index, was calculated, providing a powerful, unified metric to rank substrate efficacy. WF-based substrates exhibited increased porosity and diminished water retention, whereas media enriched with CS and BSG enhanced moisture availability, particularly at 20–40 PR. The bulk density was highest at PR40 for both WF and BSG treatments, and at PR20 in CS-based substrates. Electrical conductivity increased in CS and BSG treatments with rising PR levels. The results on the vegetative growth of ornamental sages have highlighted that differential PR rates are required depending on the specific organic by-product and plant genotype. In ‘Victoria’, GI indicates that a 20% replacement of peat with BSG provided the optimal conditions for holistic plant development; the lowest GI for WF substrates across nearly all peat replacement levels indicated that it was the most detrimental alternative for this cultivar. In ‘Amistad’, the analysis of the GI scores revealed that the CS20 and BSG20 of peat replacement yielded the highest overall growth, with GI scores significantly greater than those of the peat control. CS10 and BSG40 also showed high GI scores in ‘Amistad’. WF10 had GI scores similar to those of the peat control. In general, the GI-based approach confirms that moderate inclusion of brewer’s spent grain (BSG20) is a highly effective peat replacement for both genotypes. At the same time, coffee silverskin (CS) is particularly effective for the ‘Amistad’ genotype. This analysis underscores that optimal substrate formulation is not only dependent on the amendment type and rate but also critically on the plant genotype. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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15 pages, 1134 KB

Open AccessArticle

Potential of Pine Bark to Replace Perlite in Coir-Based Substrates: Effects on Nutrient Uptake, Growth, and Phytochemicals in Lettuce Under Two Salinity Levels

by Gonçalo C. Dias, Rui M. A. Machado, Isabel Alves-Pereira, Rui A. Ferreira and Nazim S. Gruda

Plants 2025, 14(16), 2577; https://doi.org/10.3390/plants14162577 - 19 Aug 2025

Cited by 3 | Viewed by 1511

Abstract

Enhancing the sustainability of growing media is an important objective in soilless vegetable cultivation. Here, we evaluated the potential of pine bark to replace perlite in coir-based substrates for lettuce (Lactuca sativa L. cv. ‘Godzilla’) cultivation. The experiment followed a factorial design with two coir-based substrate blends—one amended with perlite and the other with pine bark—and two nutrient solution EC levels (1.5 ± 0.2 and 2.5 ± 0.2 dS m⁻¹). The plants were cultivated in Styrofoam containers containing a substrate mix of 80% coir, 12% compost, and 8% perlite or pine bark (v/v). Replacing perlite with pine bark did not affect leaf macronutrient concentrations but increased leaf Fe and B levels. Increasing the EC of the nutrient solution increased leaf N, P, and K, with a significant rise in nitrogen. The substitution of perlite with pine bark in coir-based substrates did not affect leaf dry weight, head fresh weight, or chlorophyll content, total phenols, ascorbic acid, or proline, even under different salinity levels. The findings indicate the pine bark is an alternative to perlite, supporting comparable agronomic and quality outcomes in lettuce. Further research is recommended to confirm these results in crops with longer growing cycles. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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16 pages, 940 KB

Open AccessEditor’s ChoiceArticle

Effects of Seedling Substrate and Hydroponic Versus Aquaponic Nutrient Solution on Growth, Nutrient Uptake, and Eco-Physiological Response of Lemon Basil (Ocimum × citriodorum)

by Linda Signorini, Giuseppe Carlo Modarelli, Prospero Di Pierro, Antonio Luca Langellotti, Chiara Cirillo, Stefania De Pascale and Paolo Masi

Plants 2025, 14(13), 1929; https://doi.org/10.3390/plants14131929 - 23 Jun 2025

Cited by 4 | Viewed by 2339

Abstract

Lemon basil (Ocimum × citriodorum) is a highly valued aromatic plant renowned for its distinct citrus aroma. This study aimed to evaluate sustainable substrates and cultivation systems for its production. Two complementary and sequential experiments were conducted: an initial experiment designed to compare coconut fiber mixed in varying proportions with perlite to rock wool, evaluating their effectiveness during germination and early growth (experiment 1), and a subsequent experiment aimed at assessing plant performance in a decoupled aquaponic system relative to hydroponics utilizing the best-performing coconut fiber-perlite mixture from the first phase along with rock wool as substrates (experiment 2). The substrate with 70% coconut fiber and 30% perlite (F70:P30) significantly improved seed germination, leaf number, and total leaf area of seedlings. The decoupled aquaponic cultivation system resulted in a 52.5% increase in flavonoid content, accompanied by higher calcium and magnesium uptake in stems and roots compared to hydroponics. These findings clearly underscore the potential of coconut fiber substrates mixed with perlite as sustainable alternatives to rock wool, reducing environmental impact, disposal costs, and health risks. Similarly, aquaponic cultivation emerges as a valuable strategy for sustainable lemon basil (Ocimum × citriodorum) production, offering comparable yields to hydroponics while improving plant nutritional and phytochemical quality through beneficial plant-microbe interactions. These results provide practical evidence supporting the adoption of environmentally friendly substrates and cultivation practices, thus contributing significantly toward sustainable intensive vegetable production systems. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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19 pages, 7245 KB

Open AccessArticle

Nitrogen Immobilization by Wood Fiber Substrates Strongly Affects the Photosynthetic Performance of Lettuce

by Lingyi Wu, Ruohan Li, Juncheng Liu, Wenzhong Cui, Zhiyong Qi and Wanlai Zhou

Plants 2025, 14(10), 1518; https://doi.org/10.3390/plants14101518 - 19 May 2025

Cited by 6 | Viewed by 1956

Abstract

Wood fiber substrates are widely used as peat substitutes in horticulture, but the impact of their high carbon-to-nitrogen ratio on nitrogen immobilization and crop photosynthetic performance remains unclear. This study systematically examined the effects of wood fiber substrates on lettuce photosynthetic performance and underlying physiological mechanisms using pot experiments. Two substrate treatments—peat (control) and wood fiber—were combined with three nitrogen levels: low, medium, and high (63, 127, and 210 mg N·L⁻¹). Results indicated that wood fiber substrates significantly reduced the availability of fast-acting nitrogen, leading to a substantial decrease in lettuce biomass (39.0–56.8%), total nitrogen content (7.2–39.9%), and chlorophyll content (13.7–36.2%). Chlorophyll fluorescence kinetics analysis revealed that wood fiber substrates impair photosystem function through multiple pathways. At the early stage (15 days), key effects included structural damage to the donor side of PSII(Photosystem II), indicated by L and K peaks, and inhibited electron transfer on the PSI(Photosystem I) acceptor side (δRo decreased by 15.08–27.90%, along with a reduction in W_OI amplitude). The findings provide an important theoretical basis for optimising nitrogen management strategies for wood fibre substrates. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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20 pages, 2315 KB

Open AccessArticle

Fulvic Acid, Amino Acids, and Vermicompost Enhanced Yield and Improved Nutrient Profile of Soilless Iceberg Lettuce

by Beyza Keskin, Yelderem Akhoundnejad, Hayriye Yildiz Dasgan and Nazim S. Gruda

Plants 2025, 14(4), 609; https://doi.org/10.3390/plants14040609 - 18 Feb 2025

Cited by 12 | Viewed by 5215

Abstract

Soilless cultivation systems are sustainable innovations in modern agriculture, promoting high efficiency per unit area, supporting food sustainability, and addressing the growing demand for high-quality produce with minimal environmental impact. This study evaluates the effects of fulvic acid, amino acid, and vermicompost biostimulants on the growth, yield, and nutrient profile of soilless-grown iceberg lettuce (Lactuca sativa var. capitata) in floating culture under controlled glasshouse conditions. Two experiments were conducted to determine the most effective concentrations and combinations of biostimulants. In the first experiment, varying doses of fulvic acid (40 and 80 ppm), amino acid (75 and 100 ppm), and vermicompost (1 and 2 mL L⁻¹) were tested alongside a control. Optimal doses were identified based on their positive effects on lettuce growth and yield. The second experiment examined combinations of fulvic acid, amino acid, and vermicompost extract compared to a control. Biostimulants improved lettuce growth, nutrient uptake, and antioxidants. Vermicompost boosted root biomass and leaf area, while fulvic acid and amino acid reduced nitrates and increased dry matter. Fulvic acid and vermicompost resulted in the highest yield (17.15 kg/m², 18.2% increase), and the combined treatment maximized antioxidants, increasing vitamin C by 17.16%, total phenols by 52.54%, and flavonoids by 52.38%. These findings highlight the potential of biostimulants as eco-friendly solutions for optimizing lettuce production in soilless systems. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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19 pages, 1837 KB

Open AccessArticle

Nutrient Use Efficiency and Cucumber Productivity as a Function of the Nitrogen Fertilization Rate and the Wood Fiber Content in Growing Media

by Rita Čepulienė, Lina Marija Butkevičienė and Vaida Steponavičienė

Plants 2024, 13(20), 2911; https://doi.org/10.3390/plants13202911 - 17 Oct 2024

Cited by 8 | Viewed by 3807

Abstract

A peat substrate is made from peat from drained peatlands, which is a limited resource. A realistic estimate is that 50% of the world’s wetlands have been lost. Peat is used in horticulture, especially for the cultivation of vegetables in greenhouses. The consequences of peatland exploitation are an increase in the greenhouse effect and a decrease in carbon stocks. Wood fiber can be used as an alternative to peat. The chemical properties of growing media interact and change continuously due to the small volume of growing media, which is limited by the growing container. This study aims to gain new knowledge on the impact of nutrient changes in the microbial degradation of carbon compounds in wood fiber and mixtures with a peat substrate on the content and uptake of nutrients required by plants. The cucumber (Cucumis sativus L.) variety ‘Dirigent H’ developed in the Netherlands was cultivated in growing media of a peat substrate and wood fiber: (1) peat substrate (PS); (2) wood fiber (WF); (3) wood fiber and peat substrate 50/50 v/v (WF/PS 50/50); (4) wood fiber and peat substrate 25/75 v/v (WF/PS 25/75). The rates of fertilization were the following: (1) conventional fertilization (CF); (2) 13 g N per plant (N₁₃); (3) 23 g N per plant (N₂₃); (4) 30 g N per plant (N₃₀). The experiment was carried out with three replications. As the amount of wood fiber increased, the humidity and pH of the growing media increased. The fertilization of the cucumbers with different quantities of nitrogen influenced the nutrient uptake. The plants grown in the 50/50 and 25/75 growing media had the best Cu uptake when fertilized with N₂₃. When the plants grown in the wood fiber media and the 50/50 media were fertilized with N₁₃, N_23, and N₃₀, the Mn content in the growing media at the end of the growing season was significantly lower than the Mn content in the media with conventional fertilization. Thus, nitrogen improved the uptake of Mn by the plants grown not only in the wood fiber, but also in the combinations with a peat substrate. Growing plants in wood fiber and fertilizing them with N₁₃ can result in the optimum uptake of micronutrients. The number and biomass of cucumber fruits per plant were influenced by the amount of wood fiber in the growing media and the application of nitrogen fertilizer. The highest number of fruits and biomass of fruits per plant obtained were significantly higher when the cucumbers were grown in WF/PS 50/50 growing media with additional N₁₃ fertilization. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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15 pages, 2322 KB

Open AccessArticle

Assessment of Vegetable Species for Microgreen Production in Unheated Greenhouses: Yield, Nutritional Composition, and Sensory Perception

by Pabla Rebolledo, Gilda Carrasco, Claudia Moggia, Pedro Gajardo, Gabriela Rodrigues Sant’Ana, Fernando Fuentes-Peñailillo, Miguel Urrestarazu and Eduardo Pradi Vendruscolo

Plants 2024, 13(19), 2787; https://doi.org/10.3390/plants13192787 - 4 Oct 2024

Cited by 3 | Viewed by 2341

Abstract

Cultivating microgreens in central-southern Chile in unheated greenhouses offers a viable and productive alternative to growers. In 2023, two experiments were conducted in autumn and spring. These experiments involved the production of microgreens of eleven vegetable species. The tray system with the substrate was employed. Subsequently, agronomic, nutritional, and sensory perception variables were assessed. Despite notable fluctuations in external temperatures between these seasons, a diverse array of microgreens can be successfully cultivated, meeting local consumer preferences. Research indicates that microgreens grown under these conditions exhibit high nutritional quality, serving as a rich source of essential nutrients and bioactive compounds beneficial to human health. This nutritional value remains consistent across autumn and spring, establishing microgreens as a reliable and valuable food option. The observed acceptance and purchasing intentions among the surveyed population suggest a promising market opportunity for introducing these products regionally. Consumers appreciate microgreens’ quality and nutritional advantages, underscoring their potential. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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16 pages, 4240 KB

Open AccessArticle

Rapid Reduction of Phytotoxicity in Green Waste for Use as Peat Substitute: Optimization of Ammonium Incubation Process

by Wenzhong Cui, Juncheng Liu, Qi Bai, Lingyi Wu, Zhiyong Qi and Wanlai Zhou

Plants 2024, 13(17), 2360; https://doi.org/10.3390/plants13172360 - 24 Aug 2024

Cited by 1 | Viewed by 1623

Abstract

The rapid growth of the horticultural industry has increased demand for soilless cultivation substrates. Peat, valued for its physical and chemical properties, is widely used in soilless cultivation. However, peat is non-renewable, and over-extraction poses serious ecological risks. Therefore, sustainable alternatives are urgently needed. Ammonium incubation, a novel method to reduce phytotoxicity, offers the potential for green waste, a significant organic solid waste resource, to substitute peat. This study optimized the ammonium incubation process to reduce green waste phytotoxicity. It systematically examined different nitrogen salts (type and amount) and environmental conditions (temperature, aeration, duration) affecting detoxification efficiency. Results show a significant reduction in phytotoxicity with ammonium bicarbonate, carbonate, and sulfate, especially carbonate, at 1.5%. Optimal conditions were 30 °C for 5 days with regular aeration. Under these conditions, ammonium salt-treated green waste significantly reduced total phenolic content and stabilized germination index (GI) at a non-phytotoxic level (127%). Using treated green waste as a partial peat substitute in lettuce cultivation showed promising results. This low-cost, low-energy method effectively converts green waste into sustainable peat alternatives, promoting eco-friendly horticulture and environmental conservation. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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Review

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16 pages, 615 KB

Open AccessReview

Nitrogen Immobilization in Organic Media: A Double-Edged Sword Affecting the Utilization of Green Waste as Growing Media

by Ruohan Li, Wenzhong Cui, Min Zhang, Zhiyong Qi and Wanlai Zhou

Plants 2026, 15(9), 1298; https://doi.org/10.3390/plants15091298 - 23 Apr 2026

Cited by 1 | Viewed by 457

Abstract

This review proposes a “phenomenon–mechanism–regulation” framework for understanding nitrogen immobilization during the conversion of green waste into growing media. Nitrogen immobilization acts as a double-edged sword: intense short-term immobilization, typically occurring within the first 1–2 weeks after substrate establishment, can rapidly deplete mineral nitrogen and induce plant nitrogen deficiency, whereas the immobilized nitrogen is subsequently incorporated into microbial biomass and lignin-associated organic pools, forming a slow-release reservoir that enhances nitrogen retention and reduces leaching losses. Owing to its extremely high C/N ratio (often >100) and the coexistence of labile carbon fractions and recalcitrant compounds (e.g., lignin and phenolics), green waste exhibits substantially stronger immobilization potential than conventional media. Empirical evidence indicates that nitrogen immobilization can reach 10–115 mg N·L⁻¹ within a few days in wood-derived substrates, and additional fertilization of up to 100 mg N·L⁻¹ may be required to maintain crop growth. Mechanistically, nitrogen immobilization is governed by the coupling of microbial assimilation—driven by stoichiometric C/N imbalance (typically triggered when C/N > 20–25)—and abiotic chemical fixation, including reactions between NH₄⁺/NO₂⁻ and lignin-derived phenolics forming stable organic nitrogen compounds. The relative dominance of these pathways is jointly regulated by carbon quality, nitrogen form, and pH. Based on these mechanisms, regulatory strategies are summarized at multiple scales, including feedstock pretreatment to reduce labile carbon availability, substrate formulation to optimize C/N balance, and model-assisted intelligent fertigation to synchronize nitrogen supply with crop demand. Overall, this study provides a theoretical basis for improving green waste valorization and promoting sustainable horticultural production. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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16 pages, 907 KB

Open AccessReview

Kenaf Core as an Alternative Soilless Growing Medium: A Review

by Conner C. Austin, S. Brooks Parrish, David G. Clark and Ann C. Wilkie

Plants 2026, 15(4), 666; https://doi.org/10.3390/plants15040666 - 23 Feb 2026

Cited by 1 | Viewed by 729

Abstract

Kenaf (Hibiscus cannabinus) core, an abundant renewable byproduct rich in cellulose and hemicellulose, has emerged as a candidate to replace or supplement peat and coco coir in soilless culture. This review synthesizes the physical, chemical, and biological performance of ground kenaf core and benchmarks it against conventional substrates. Kenaf core exhibits low bulk density (0.06 to 0.15 g cm⁻³), high total porosity (approximately 90%), and substantial plant available water (approximately 42%), supporting root aeration and water supply. Its pH (6.0–7.2) is near optimal for most crops, whereas electrical conductivity (EC) (3.2–4.7 dS m⁻¹) can exceed recommended ranges for salt-sensitive species, which necessitates pre-leaching or blending. Growth studies show comparable shoot and root performance in blends containing 20 to 70% kenaf, with composted kenaf often outperforming raw core. Pure kenaf generally requires more frequent irrigation and may shrink at high proportions. We outline processing variables such as core purity, particle size, composting, and leaching that govern stability and plant response, identify critical data gaps (including standardized EC and pH methods, and long-term shrinkage), and frame a sustainability agenda. Practically, studies to date indicate that pre-leached kenaf core, incorporated at up to about 70% by volume into peat or coir-based blends with structurally stable components such as perlite, can maintain growth and quality for several ornamental and bedding crops under greenhouse and nursery conditions. At the same time, reports of poor performance in some conifers and early suppression in direct-sown vegetables underscore that the suitability of kenaf-based substrates remains crop specific and dependent on material processing and management. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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23 pages, 1821 KB

Open AccessReview

Beyond Peat: Wood Fiber and Two Novel Organic Byproducts as Growing Media—A Systematic Review

by Anna Elisa Sdao, Nazim S. Gruda and Barbara De Lucia

Plants 2025, 14(13), 1945; https://doi.org/10.3390/plants14131945 - 25 Jun 2025

Cited by 7 | Viewed by 3414

Abstract

Environmental concerns drive the search for sustainable organic alternatives in horticultural substrates. This review critically examines three agro-industry renewable byproducts—wood fiber, coffee silverskin, and brewer’s spent grain—as partial peat substitutes. We aimed to comprehensively analyze their origin, processing methods, current applications, and key physical, hydrological, and chemical properties relevant to horticultural use. In soilless culture, wood fiber can be used as a stand-alone substrate. When incorporated at 30–50% (v/v) in peat mixtures, it supports plant growth comparable to peat; however, higher proportions may restrict water and nutrient availability. Coffee silverskin demonstrates high water retention and nutrient content, but its inherent phytotoxicity requires pre-treatment (e.g., co-composting); at concentrations up to 20%, it shows promise for potted ornamental crops. Brewer’s spent grain is nutrient-rich but demands careful management due to its rapid decomposition and potential salinity issues; inclusion rates around 10% have shown beneficial effects. In conclusion, when used appropriately in blends, these bio-based byproducts represent viable alternatives to reduce peat dependence in vegetable and ornamental cultivation, contributing to more sustainable horticultural practices. Future research should optimize pre-treatment methods for coffee silverskin and brewer’s spent grain, investigate long-term stability in diverse cropping systems, and explore novel combinations with other organic waste streams to develop circular horticultural substrates. Full article

(This article belongs to the Special Issue Driving Sustainability: Innovations in Producing Eco-Friendly Substrates for Soilless Culture Systems)

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