During the past decades, peat has been the major constituent of substrates thanks to its physico-chemical properties favouring plant growth. At the same time, its high carbon content has risen concerns about its environmental impact. In 2022-2024, we investigated (1) what is the use and after-use of the horticultural peat extracted and used in Estonia; (2) what is the speed of peat decomposition during its use, and (3) where does peat carbon reach after use? For that, we conducted a survey among the plant growers and peat extracting companies that was complemented by the information from databases. In parallel, we conducted a laboratory study to measure greenhouse gases flux and carbon balance in the substrate during plant growth. During that, the major groups of ornamental plants (hyacinth, cornflower, azalea), vegetables (lettuce, broccoli, cauliflower) and forest tree seedlings (bare-rooted and potted) were grown and sampled.

We found that from 6,3 million m³ of peat extracted in Estonia in 2022, only 0,2 million m³ was the domestic use, mostly by small producers to grow various plants. The time of substrate use was generally relatively short and variable, from 1 month to 5 years, in average 4-6 months. After its use, almost all of the substrate (composted or not) reached to the soil in garden, field, forest or elsewhere: with the root ball, composted or straight. There, used peat substrate acts as a soil improver.

The carbon flux of all cultures was binding during growing (carbon sink), and the overall carbon gain by plant growth much higher than the losses from soil. Chemical analyses showed that Estonian peats have relatively low C (47,4%) and high lignin (53,1%) content, the latter slowing down decomposition that in soils is about 2% per year, but depends highly on soil properties. RothC models have shown that due to high lignin content, about 29% of Estonian peats remain stable in the soil after 100 years, therefore highlighting the inaccuracies in the current greenhouse gases reporting methodology.

The horticultural industry faces increasing pressure to find sustainable alternatives to peat due to environmental concerns associated with its extraction and use. This study investigates the potential of steam-exploded wood fibers (SEWF) derived from spruce and pine as peat-free media. Cucumber pot experiments were conducted using SEWF and SEWF-peat mix (50/50). Three levels of fertilization (1.2, 2.4 and 4.8 mS/cm) were supplied through irrigation using two different irrigation strategies, sub-irrigation and surface irrigation. Measurements included EC, pH, plant height, leaf area, fresh and dry weight, and relative chlorophyll content.

Plants grown in SEWF with peat demonstrated slightly better growth performance than sole SEWF media. However, dry weight measured from the cucumbers irrigated with the highest fertilization level were about equal for both growth medias with surface irrigation. This suggests that when provided with adequate nutrients, the SEWF medium can support cucumber growth as effectively as the SEWF-peat mix. 

Biomass differences were observed in SEWF media based on the irrigation strategy. Surface irrigation consistently resulted in higher cucumber dry weights across all fertilization levels. At a fertilization level of 1.2 mS/cm, surface irrigation produced a dry weight of 2.06 g, compared to 1.09 g with sub-irrigation. At 2.4 mS/cm, dry weights were 5.07 g and 3.29 g for surface and sub-irrigation, respectively. At 4.8 mS/cm, surface irrigation yielded 10.1 g, while sub-irrigation resulted in 8.40 g (n=5). In the peat-SEWF mix, differences in cucumber dry weight between irrigation strategies decreased at higher fertilization levels, while growth in pure peat consistently resulted in higher dry weights regardless of fertilization or irrigation strategy.

The findings emphasize the critical roles of irrigation strategy and fertilization levels in optimizing plant growth in SEWF media, suggesting nutrient availability may limit growth at lower fertilization levels due to the material's physical or chemical properties affecting nutrient dynamics.

Cattail (Typha ssp.) obtained from paludiculture could represent a sustainable source of raw materials for the production of growing media in horticulture. However, it is not possible to use cattail in unprocessed form, as nitrogen immobilization rate is too high. Predominantly, immobilization is due to the high ratio between easily degradable carbon sources and nitrogen in the biomass. Therefore, possibilities must be found to remove those carbon sources from the substrate or to protect them against microbial degradation. The aim of this study was to reduce the proportion of easily degradable hemicelluloses and sugars and thus increase the percentage of the more recalcitrant lignin in the cattail chops by thermal and thermal-hydrolytic treatments. For this purpose, cattail chops, were treated by different temperatures, treatment times as well as with and without the addition of sulfuric acid. The effect of these treatments on nitrogen immobilization and plant tolerability of the obtained material was tested in several incubation studies and vegetations tests.

The demand for sustainable alternatives to peat in horticultural growing media is arising. Therefore new materials are developed and tested as peat alternatives. In this study we investigated the microbial consortia of hardwood fibres developed in the project “Production and use of wood fibre as a peat substitute (HoFaTo)”.

In addition to the main project objectives, the study extended its scope to analyse the microbiome of the newly developed hardwood fibres. Advanced sequencing technologies were applied to provide insight into the microbial consortia associated the chosen hardwood fibres. The aim was to understand the impact of substrate composition on the rhizosphere microbiota and its potential implications for plant health and nutrient cycling. The outcome of this research is of significant value, providing comprehensive insights into the feasibility of using modified hardwood fibres as a sustainable alternative to peat in horticultural growing media to support healthy plant growth.

The search for sustainable alternatives to conventional hydroponic substrates in Vertical Indoor Farms (VIF) is increasingly important due to growing demands for environmental compatibility and resource efficiency. Many common substrates, like rockwool or cocos fiber, are either not biodegradable or create disposal challenges or environmental concerns. Biodegradable alternatives could reduce environmental impact, promote sustainable horticulture, and allow substrates to be composted after use. Ideal alternative substrates should be regionally available in large quantities and cost-effective to source. However, hydroponic substrates must maintain structural stability throughout cultivation to ensure proper plant support and efficient water and nutrient supply. Biodegradation should occur only after cultivation to preserve the medium's physical properties. This study investigates wax-coated hemp-miscanthus fiber mixtures as an alternative substrate for hydroponic cultivation in VIF. The aim is to modify the known fibers properties through wax coating and specific heat treatments to ensure improved structural stability of these regionally available, but often fast-degrading fibers throughout cultivation. Several forms (cubes, plates) of wax-coated fibers are tested for suitability in hydroponic cultivation of currently VIF-relevant crops like Pak Choi (Brassica rapa subsp. chinensis) or Mint (Menta spp.). The analysis includes microscopic examinations of fiber structure, measurement of substance loss to assess biodegradation, and plant growth analysis through biomass production measurements. Developing innovative, environmentally friendly, and biodegradable substrates could significantly contribute to meeting sustainability goals in VIF while maintaining the advantages of hydroponic cultivation. The Federal Ministry of Food and Agriculture (BMEL) funded the research, based on a resolution of the German Bundestag.

Due to an increasing demand of growing media and the concurrent reduction of peat, the need for alternative growing medium constituents is increasing. Established products as wood fiber, green waste compost, composted bark or coir are not available in sufficient quantities, to cover demand. Thus, we tested a broad range of renewable raw materials for their suitability as growing medium constituent, e.g. spelt husks, hop bines, fen paludiculture biomass, bagasse, hazelnut and sweet lupine shells and separated biogas residues. If necessary, the structure of the materials was improved by milling and pulping, respectively.

Chemical, physical and biological properties of the materials was analyzed, whereby a special focus was set on plant compatibility and microbial degradability. Therefore, a combined and modified plant response test with Chinese cabbage was done. Additionally to rating of plant compatibility, a nitrogen balance was calculated, to assess nitrogen drawdown of the materials. Furthermore, microbial degradability was assessed by a newly developed respirometric method, whereby the material is incubated for five days in 2.5 l vessels and oxygen uptake is measured continuously by pressure heads (OxiTop®).

With the exception of chopped hop bines and material of Juncus effusus all materials tested showed a high plant compatibility. However, several of them, e.g. all other plants from fen paludiculture, had a significant N immobilization and can only be used in higher proportions after any kind of preprocessing as composting or fermentation. Quite good results were found for biogas residue, especially if no animal manure or slurry was used as substrate. The potential of the various materials as growing medium constituent is discussed.

This study aimed to evaluate the effect of using walnut shell in coir-based substrates on lettuce yield and quality. To achieve this, an experiment was conducted with five treatments: coir as the control (C) and four coir-based mixes. Three of these mixes included walnut shells at different ratios (1:1, 1:0.5, and 1:0.25 v/v), and one mix included walnut shells and biochar (10:1.5:1 v/v). The walnut shell, triturated into particles ranging from 0.35 to 3.5 mm, had a pH of 4.5, an electrical conductivity of 1.4 dS/m, and a bulk density of 0.45 g/cm³. Lettuce seedlings were transplanted into Styrofoam planting boxes filled with the substrate and irrigated daily by drip with a complete nutrient solution. The yield (fresh yield) (7.1 kg/m²) in the coir-based mix with walnut shell and biochar was not significantly different from that obtained with coir alone. Mixes with different ratios of walnut shell led to a decrease in fresh yield, probably due to an increased volume of water-drained water. Despite this, shoot dry weight was only lower in plants grown in the 1:1 mix. Walnut shell in coir-based mixes substantially reduced shoot nitrate accumulation, decreasing nitrate levels from 4000 mg NO₃⁻/kg fresh weight in coir to below 2000 mg NO₃⁻/kg fresh weight. Shoot total phenols and ascorbate levels were not affected by walnut shell inclusion in mixes. Combining walnut shells with biochar in a coir-based substrate can improve lettuce quality without affecting yield. When using walnut shell only with coir, the lower ratio of walnut shell should be applied, and the irrigation scheduling must be optimized for the coir-walnut shell mix. 

The substrates used in horticultural nurseries are primarily composed of peat. The availability of peat capable of meeting the needs of both European and non-European users is uncertain, with a foreseeable future scarcity and a subsequent increase in costs. This is due to restrictive policies on its extraction and use, as well as the need to reduce the carbon footprint throughout the entire life cycle of the substrate. In addition, there is an increasing scarcity of highly decomposed peat, the preferred raw material for the production of young plants, due to its well-known binding properties in substrates. The substrate breakdown without highly decomposed peat is a common problem, especially during early transplants or when handling seedlings with underdeveloped root systems. The reduced availability of this type of peat on the market makes it necessary to find binding agents. These additives must be non-phytotoxic and not negatively affect the quality of the produced plants. They must also exhibit good binding properties, ease of application, and reasonable cost. This research presents the results of a multi-year study aimed at identifying mineral or organic binding agents, both of natural and synthetic origin, capable of providing adequate binding effects to substrates with lower amounts of highly decomposed peat or those containing also other organic matrices as well. The tests were conducted on blocking substrates and plugs, using respectively lettuce and tomato as models. The behaviour of various binding agents and different substrates was studied by simulating mechanical shocks during transplanting and handling operations. In addition, key biometric measurements were taken on seedlings ready for transplanting to evaluate the influence of the binding agents on seedling development. The study provided promising results, in some cases showing no significant differences from the control based on highly decomposed peat, in terms of resistance to mechanical shocks and balanced seedling development.

Mixed results are reported when biochar and wood fiber are used in growth media, and this is largely dependent on the source, nutrient content mechanical modifications, pyrolytic conditions, and mixing ratios with peat. Five pot experiments were conducted, 3 with Chinese cabbage (Brassica rapa subsp. pekinensis) and 2 with tomato (Solanum lycopersicum). The experiments used biochar and wood fiber from multiple sources with varying physical properties and pyrolysis conditions at peat replacement ratios of 10, 20, 30 and 40% (v/v) for biochar and 25 and 50% (v/v) for wood fiber, all compared to 100% peat. Both wood fiber and biochar did not affect germination rates of Chinese cabbage at the assessed mixing ratios. Over three experiments, the type of wood fiber did not significantly affect Chinese cabbage and tomato biomass while the mixing ratio with peat was a significant factor only for Chinese cabbage biomass production across two trials (P < 0.001 and P = 0.001). In the two Chinese cabbage wood fiber trials, mixing rates of 50% (v/v) yielded lower biomass than those at 25%. The type of biochar and its mixing ratio where both significant in altering biomass of Chinese cabbage and tomato. In these trials, generally higher content of biochar in the growth media (40%) yielded lower biomass for Chinese cabbage and tomato compared to lower rates of addition and 100% peat. Results indicate that there was not a detectable difference between the various types of wood fiber assessed in this experiment and that mixing ratios and their effect on different plant species needs further research. Regarding biochar, careful selection of biochar type and mixing ratio is recommended, both requiring to be optimized according to the nutrient availability from the material and crop type.

The exploration of local resources as growth media alternatives to coir for soft fruit production is essential particularly for coir importing countries to improve self-sufficiency and environmental sustainability. The agronomic performance of novel wood fiber-based formulations containing biochars (3 types), composted green waste (2 types), barks (2 types), and quarry waste (1 type) was compared with coir, and other 2 commercial media (peat and rockwool) for growing strawberries. A two-year glasshouse experiment was run with each treatment replicated 8 times in the first year and replicated 5 times in the second year. The same growth media was re-used in the second year with replanting of new strawberry plants. For both seasons, there were no statistical differences (P > 0.05) between class 1, class 2, and total marketable berry yields per plant between the various growth media, however all yields were significantly lower than expected commercial yields in Ireland. A similar trend was observed for berry count per plant, plant biomass and chlorophyl content. However, in the first season, a 50% composted green waste mix, a 20% quarry waste mix, a 40% biochar mix produced significantly smaller berries than coir. The same 20% quarry waste mix also produced strawberry above-ground biomass with significantly less P content than coir, while the same 40% biochar mix produced biomass with significantly less Ca content than coir. Results reveal that wood fiber based alternative growth media has good potential as commercial growth media, but they present complex relationships in the root zone that not only affects water regimes and uptake but also nutrient uptake even when the media are fertigated with the same solution and similar irrigation frequency. Further studies on optimization of alternative media through altering irrigation frequencies and fertigation solutions are recommended.

For reasons of climate protection and nature conservation, the reduction of peat content in growing media in all areas of horticulture is a declared environmental policy goal in Germany (e.g. Climate Protection Plan 2050). Both, the optimization of crop safety in the use of widely applied peat substitutes and the investigation of new materials in horticultural growing media is therefore urgently needed and is currently being investigated in numerous research projects.

As part of the ToPGa joint project, the raw materials fibre nettle and fermentation products of biogas plants were tested for their suitability as growing media components. Both raw materials were systematically analyzed in several test phases in terms of substrate analysis and plant cultivation in a test procedure for peat substitutes. In another experiment, various substrate mixtures with a maximum peat content of 50% were created in order to test the transferability of results of an experimental design for formulations based mixture model from vegetable nursery plants cultivation to potted herbs and ornamental plants.

Besides fibre nettle shives and a nutrient depleted fermentation product, established peat substitutes were added as mixture components. Peat and a growing medium established in practice were used as controls. In the ornamental plant cultivation division, petunia and in the potted herbs division, basil was examined as a crop in tests under practical conditions. Plant growth of petunia in the tested mixtures was approx. 60 % lower than in the control variants, which was due to a very dense substrate and the associated low air capacity and low root growth. In the case of basil, the growth reduction between the test variants and the control was 30 %. In order to transfer the mixture model to other crops, further adjustments are necessary, e.g. taking more into account the particle sizes of the growing medium.

The available substrates for soilless cultivations are limited and their production is based on resource-intensive materials in particular for rockwool and perlite. The exploration of alternative natural materials for substrate applications is critical for enhancing material innovation. Hydrogels in agriculture have been created applying different methods and materials but few studies have focused on investigating the practical assessment of them as plant soilless substrates. Alginate, a natural polysaccharide derived from brown algae, was chosen as the base for hydrogel development due to its plant biostimulant properties. Based on previous trials, using natural alginate based hydrogel as hydroponic substrate requires an environment where temperature and humidity are continuously monitored to control the material´s degradation. Indoor vertical farming systems provide the ideal conditions for this level of control.

This study aimed to develop a novel alginate-based hydrogel with enhanced biodegradability and biostimulant properties to promote seed germination. A newly developed natural alginate-based hydrogel, characterized by its fast and simple production process, was tested for its effects on the germination of pharmaceutical plants relevant to indoor vertical farming, such as mint (Mentha spp.), Madagascar periwinkle (Catharanthus roseus), and roseroot (Rhodiola rosea). The hydrogels were simply prepared using the cross-linking reaction that occurs between the alginate solution and the calcium of a calcium chloride solution.

The key results highlighted the potential of this material to be used as a biostimulant substrate and as an alternative solution to prevent root loss in transplant application. This aspect is particularly crucial for medicinal plants that store high valuable bioactive compounds in their roots. The results underscore the hydrogel's promise in enhancing seed germination and supporting the sustainable cultivation of high-value medicinal plants.

The project is funded by the Bayerisches Staatsministerium für Wissenschaft und Kunst (STMWK).

Global increase in poultry production has led to substantial rise in poultry waste, presenting environmental and management challenges. However, this nutrient-rich waste can serve as a valuable resource for agricultural production. This project investigated the potential to formulate compost suitable for application in urban residential areas from local poultry and horticulture waste, examining its effect on vegetable growth. Compost formulations were generated by blending poultry waste with horticulture waste in ratios of 40:60, 80:20, and 85:15 (v/v), composting it in an aerobic digester at 45 - 60 °C for 1 - 2 weeks. The 85:15 ratio yielded optimal results achieving: C:N ratio of 15.7, pH 6.4, electrical conductivity (EC) of 8.7 mS/cm, all within the recommended ranges of Singapore standards for compost, SS628:2017. In addition, the compost was found to free of Salmonella enterica serovar Enteritidis and Typhimurium. Greenhouse trials assessed the effects of formulated compost (FC) on baby pak choi (Brassica rapa subsp. chinensis) growth and determined a suitable commercial potting mix (CPM) to compost ratio of 95:5 (v/v), with a 70% increase in vegetable yields compared to CPM only (100:0). Furthermore, odour tests using the test method EN 13725:2003 and surveys with residents indicated that FC had low to no detectable odour, indicating that it would be suitable for use in urban residential areas. In conclusion, CPM:FC ratio of 95:5 (v/v) was effective at increasing yields with minimal odour, offering a sustainable approach for growing vegetables in urban residential areas.

There is a strong demand for replacing peat as a growing media, due mainly to the adverse environmental impacts of peat harvesting. Much work has been done investigating partial replacement of peat with processed biomass materials but little or no work - to our knowledge - on the use of these materials without any peat, possibly due to expectation of adverse results.  Coir can, of course, entirely replace peat but, like peat, it also has negative environmental and social aspects. In this investigation we sought a combination, principally comprising composted greenwaste (CGW), composted bark fines (CBF) and wood fibre (WF) which could completely replace peat.  The trials used tomato and petunia as test crops, tomato being less salt sensitive, and petunia more so.  In the first phase of trials, CGW (20-70% by volume), CBF (10-40%) and WF (20-40%) were mixed to form various treatments. In the second phase, CGW was used from 60-80% by volume, CBF at 10-20% and WF at 20-30%.  All trials had 100% fertilised peat as control.  All constituent materials were fertilized separately, based on known chemical properties, and characterised by pH, EC and bulk density. In the first phase, with tomato, the best treatments (all 100%+ compared to the control) were 25CGW:40CBF:35WF and 20CGW:40CBF:40WF. The poorest result was for 70CGW:10CBF:20WF (75% of control).  For petunia, the best results (100%+) were for the treatments 25CGW:40CBF:35WF, 20CGW:40CBF:40WF and 30CGW:40CBF:30WF.  Treatments 60CGW:20CBF:20WF and 70CGW:10CBF:20WF resulted in only 60%-70%.  In phase two, with tomato, 70CGW:10CBF:20WF and 80CGW:20WF each performed significantly better than the peat control. Treatments performing poorly included 60CGW:10CBF:30WF and 70CGW:20CBF:10WF (around 70%).  For Petunia, 60CGW:20CBF:20WF and 70CGW:10CBF:20WF were best (100%+) while 80CGW:20WF was only 75%In conclusion, it should be noted that these trials were on a small scale only and that a larger scale trial with these materials would be required to confirm these findings. Nonetheless, these results indicate there is potential to replace peat with processed biomass to 100% - at least in some situations - as long as the fertilizer regime for the chemical properties of each component material is considered. Clearly, physical properties of these combinations of materials would also need to be taken into account.

There is a great need to replace peat as a growing medium due to environmental concerns regarding industrial peat harvesting. Thus, there are numerous publications where various materials have been investigated as a partial component of a peat growing media such as woodfiber, composted greenwaste etc to partially replace peat. In most cases peat is often the base material. Research on a peat free mix or peat reduced mix suitable for organic growers is minimal. The objective of this investigation was to make progress towards a 100% peat free growing media based on composted spruce bark using organic inputs without the use of mineral fertilizers. Composting was done small piles (about 2 m³) with nitrogen source as organic poultry litter at two rates. Organic soya meal waste was also added as an additional treatment on two occasions during composting. For comparative purpose urea was also used as a nitrogen source for the composting. Composting was carried out for about 12 weeks with regular turning once a week. Regular analysis was carried out for pH, EC, NO₃-N, NH₄-N, P, K, Ca and Mg using 1:1.5 water extract. Nutrient dynamics during composting will be presented. At the end of the composting the nitrogen levels were very low except where a soya meal booster was added. In order to assess how this growing media would store 60L lots of the composted bark received 0,3,6,9,12g/L of soya meal waste was stored 4 months and samples were analysed 8 times during the period using water and CaCl₂/DTPA extract. Tomato at the propagation stage was used as a test crop. At the first harvest at 5 rough true leaves there was no response above 3g/L but at the second harvest before flowering on the first truss there was a response up to 9g/L. Additionally a short-term growing trial at using tomato again as a test crop, where the organic soya meal waste was added at the composting stage, was carried out with early and late harvest with fertilized peat media as a control. In the first harvest at 5 rough true leaves bark growing media was very slightly inferior to fertilized peat but by second harvest before flowering on the first truss, fresh weight was similar.

The aim of this research was to assess the potential of using a spent mushroom compost and livestock waste to improve the yield and quality of rocket salad in a soilless cultivation, as a part of a circular production approach in agro-alimentary systems. Three growing media were tested: Coir pith (CP; 100:0 w:w), CP+ livestock waste (CP+LW; 90:10 w:w) and CP+ spent mushroom compost (CP+MC; 50:50 w:w). Biometric plant parameters, yield and the total chlorophyll content and ion content in plant tissue were analysed. The highest yields were achieved by plants grown in CP+LW increasing by 115 and 12% in the first and second harvest, respectively, in comparison to plants cultivated in CP alone. Similarly, plants cultivated in CP+MC in the first harvest exhibited a 45% higher yield than plants grown in CP. Furthermore, plants grown in CP+LW showed significant improvements in biometric parameters and shoot/root ratio. The K, Ca and S content in the leaf tissue were significantly increased in plants grown in CP+LW and CP+MC, whereas a higher values for P was found in CP and CP+LW. Plants grown in CP+MC reached the highest nitrate accumulation (3523.52 mg kg-1 FW, on average), whilst a noticeable decrease of 57 and 32% was found in plants grown in CP alone and CP+LW, respectively. Therefore, the utilisation of a blend of livestock waste and spent mushroom compost represents a viable alternative for the attainment of sustainable production and the enhancement of ions content in rocket salad plants. 

In recent years, there has been a growing focus on integrating sustainable materials into growing media to enhance its environmental sustainability. The processing of sheep wool generates significant waste, including wool grease and short fibers, which require proper disposal or repurposing to minimize environmental impact. The potential utilization of wool waste as an amendment in growing media remains a largely underexplored area of research, with limited studies addressing its effects on plant growth, media properties, and overall sustainability within horticultural systems. In our study, we tested pelletized sheep wool waste mixed with peat at different volumes—5%, 10%, 15%, and 20%—along with varying concentration of nitrogen application- 0, 100 and 200 ppm. The results showed that media mixes with 5% and 10% wool, with or without added nitrogen, supported plant growth comparable to pure peat, with similar or improved plant height, spread, leaf count, chlorophyll content, and dry weight. pH, electrical conductivity (EC), and nutrient levels in the root zone were also better regulated. In particular, the mix containing 5% wool even without nitrogen fertigation outperformed control plants grown in 100% peat with 200 ppm of nitrogen. On the contrary, higher wool volumes (15% and 20%), regardless of nitrogen application, had adverse effects on shoot and root growth.