Introduction

Global demand for plant-based medicines continues to rise, yet cultivation of many medicinal species remains limited and underdeveloped. Approximately 90% of medicinal plants raw materials are still harvested from the wild, leading to significant ecological pressure, over-exploitation and endangering the species [1]. Even in traditionally cultivated agricultural systems, crop yield and quality are increasingly compromised by climate change, particularly due to the rising frequency of droughts, floods, and extreme weather events [2]. This is a predicament for the pharmaceutical industry, which demands the highest levels of quality, steady supply and reproducibility. This problem is further exacerbated by soil-borne pathogens, heterogeneous nutrient availability, and contamination risks, all of which can adversely affect plant health, secondary metabolite synthesis and product safety. Environmental factors and variable growth and harvesting conditions often lead to significant fluctuations in the concentration of pharmacologically active compounds, posing major challenges for consistent quality and safety in pharmaceutical production [3; 4]. Additionally, soil harvesting often damages fine roots and increases the labor-intensive process of cleaning soil residues [5]. These limitations led to growing interest in the controlled and sustainable cultivation systems, because they offer stable cultivation conditions, efficient resource use, clean root harvest and the potential to enhance the production of secondary metabolites [6]. In particular the use of hydroponics as a way to maximizing yield, secondary metabolites, and strategies to implement continuous root harvesting is gaining momentum despite the higher initial costs compared to outdoor cultivation. In this paper, we review various hydroponic systems for medicinal root crops, highlighting their advantages and presenting case studies on species such as Valeriana officinalis (valerian) and Rhodiola rosea (rhodiola).

Hydroponic cultivation systems for medicinal root crops

Figure 1: Different hydroponic cultivation systems. Key to this technique is the soilless cultivation of plants, allowing direct access of the roots to the nutrient solution [7]

Bild 1: Verschiedene hydroponische Kultivierungssysteme. Der Schlüssel dieser Technik ist die substratlose Pflanzenkultur, welche den Wurzeln einen direkten Zugang zur Nährlösung ermöglicht [7]

Hydroponics offers an effective method for cultivating medicinal plants by enabling growth in soilless growing media. As shown in figure 1, there are different hydroponic systems for the need of each crop; Nutrient Film Technique (NFT), a thin stream of nutrient solution continuously flows over the roots; Ebb & Flow (Flood and Drain) systems periodically flood the root zone and then drain it away; Deep Water Culture (DWC) suspends roots directly in an oxygen-enriched nutrient reservoir; and Aeroponics holds roots in the air, intermittently misted with nutrient solution [8]. Cultivating medicinal crops hydroponically offers several benefits over traditional soil systems: precise control of nutrient delivery, reduced risk of soil-borne diseases, accelerated growth rates and higher yields, cleaner roots requiring minimal post-harvest processing, less irrigation water, and the potential for year-round, climate-resilient production [9]. Exposed roots in hydroponic systems enable innovative approaches such as plant milking, where bioactive compounds are extracted directly from intact roots without harming the plant [10]. Additionally, hydroponic systems such as aeroponics allow for continuous root harvesting without harvesting the complete plant. Furthermore, successful hydroponic cultivation can be a foundation for transitioning to advanced systems such as indoor vertical farming. Several studies have demonstrated that hydroponic cultivation can improve both biomass yield and phytochemical content compared to conventional soil-based methods in medicinal. Tabatabaei [11] found that the highest biomass and essential oil content in valerian were obtained using Deep Water Culture, compared to aeroponics or cultivation with growing media. Rostami and Movahedi [12] evaluated valerian in an aeroponic system, reporting significant increases in plant height, root length, root volume, shoot and root dry weight, and photosynthetic pigments when roots were misted with nutrient solution enriched with naphthalene acetic acid. In other root-based medicinal crops like Withania somnifera, NFT and aeroponic systems yielded the higher biomass and secondary metabolite content compared to outdoor cultivation [13]. Conversely, Echinacea angustifolia showed higher biomass yield in hydroponics, but greater secondary metabolite content in outdoor conditions [14]. Field-grown spearmint had higher physical and chemical yields, whereas apple mint had higher yields in hydroponic systems compared to field cultivation [15]. These studies highlight the potential of cultivation of medicinal plant species and cultivars in hydroponic systems to optimize productivity. For the two case studies presented in this article, two perennial medicinal crops were selected in which root is the commercially valuable plant organ, but which differ in their cultivation periods.

Case studies: Cultivation of valerian and rhodiola in hydroponic systems

Under conventional outdoor conditions, valerian is typically cultivated for one year, whereas rhodiola requires a cultivation period of three to five years. By using hydroponic cultivation systems, the growth cycle of these perennial species can be shortened while maintaining or enhancing root biomass by higher plant density, nutrient solution optimization, environment optimization and tailored stress to increase the phytochemical quality.

Hydroponic cultivation of Valeriana officinalis (Valerian)

Valerian is an important medicinal plant in the Caprifoliaceae family, which contains sesquiterpenes such as valerenic acid, valerenal, and valeranone; compounds known for their sedative, neuroprotective, and sleep-enhancing properties [16]. Although the field cultivation of valerian is well established it is not without challenges. It is a water loving plant that requires constant access to fresh water for a period of one year [17]. This constitutes a problem as climate change, a rising demand for freshwater and frequent droughts constraining the use of water for agriculture. Hydroponic systems have been shown to reduce water consumption by up to 90 % compared to conventional soil-based agriculture [18]. However, little is known about the soilless cultivation of Valerian. Hence, in this study the dry weight and secondary metabolites content of valerian in two hydroponic cultivation systems (Nutrient Film Technique and Ebb&Flow) were tested. Three cultivars of valerian ‘Weilariana’, ‘Jagsttal’, and ‘Lubelski’ were used. These cultivars of valerian were selected for this different characteristic of the roots, ‘Weilariana’, characterized by its thick roots, high essential oil content, and low biomass yield; ‘Jagsttal’, known for its fine root texture, high biomass yield, and high content of secondary metabolites; and ‘Lubelski’, which has thicker roots but lower secondary metabolite content compared to the other cultivars [17].

Table 1: Materials and methods used for the cultivation of valerian for 6 months in NFT and EF hydroponic system (Closed irrigation system) at University of Applied Sciences Weihenstephan-Triesdorf.

Tabelle 1: Material und Methoden für den sechsmonatigen Anbau von Baldrian im NFT- und Ebbe-Flut-Kultursystem (geschlossenes Bewässerungssystem) an der Hochschule Weihenstephan-Triesdorf.

Valerian was successfully cultivated in both NFT and EF hydroponic systems. Biomass production was influenced by cultivar and cultivation system. In the NFT system, the cultivar     ‘Jagsttal’ produced significantly higher shoot and root dry weight compared to ‘Weilariana’ and ‘Lubelski’, corresponding with a greater vegetative growth and leaf area. Increased leaf area likely enhanced photosynthetic capacity, resulting in higher biomass accumulation [19]. In the EF system, ‘Jagsttal’ had higher shoot and root biomass compared to the other cultivars. Root length did not differ among cultivars, likely due to the restrictive 12 cm pot size, although increased lateral root formation was observed. Overall, biomass tended to be higher in the NFT system, possibly due to continuous root contact with the nutrient solution, which may have improved water and nutrient uptake compared to the EF system. Hydroponically cultivated valerian, particularly the high-performing cultivar ‘Jagsttal’, achieved root dry yields of up to 20.7 t ha⁻¹, which is four to five times higher than yields reported for outdoor cultivation (≈ 4.9 t ha⁻¹) [20] as shown in figure 2a. This yield was achieved within a six-month cultivation period, whereas the referenced outdoor results were obtained over one year cultivation period. Secondary metabolite accumulation varied between cultivar and cultivation system. In the NFT system, increased formation of adventitious roots was observed, which likely contributed to higher concentrations of valerenic acid derivatives [21]. Among the cultivars, ‘Jagsttal’ consis­tently exhibited the highest concentrations of sesquiterpenic acids. In the EF system, metabolite concentrations were generally lower and more variable among cultivars, potentially due to limited irrigation frequency and mild stress conditions. Overall results can be seen in figure 2b.

Figure 2: a. Dry root yield (t ha⁻¹) in the hydroponic cultivation shown as bar graphs (number of plant samples=9), compared with the maximum dried root yield of the 'Lubelsk'i cultivar grown outdoors, (shown as a line graph) [20]. b. Secondary metabolites content in mg/g DW (Valerenic acid) of the 'Lubelski' cultivar cultivated outdoors (line graph) [20] and all three cultivars cultivated in hydroponic systems (bar graph).

Bild 2: a. Ertrag der Wurzeltrockenmasse (t ha⁻¹) in der hydroponischen Kultur, dargestellt als Balkendiagramme (Anzahl der Pflanzenproben=9), im Vergleich zum maximalen Ertrag der Wurzeltrockenmasse im Freilandanbau der Sorte ‘Lubelski’ (dargestellt als Liniendiagramm) [20]. b. Sekundärmetabolitengehalt in mg/g TM (Valerensäure) der im Freiland angebauten Sorte „Lubelski“ (Liniendiagramm) [20] sowie aller drei in Hydrokultursystemen angebauten Sorten (Balkendiagramm).

Hydroponic cultivation of Rhodiola rosea (Rhodiola)

Rhodiola is a perennial medicinal plant widely used in the pharmaceutical and nutraceutical industries because of its adaptogenic properties. Extensive research into the outdoor cultivation and agronomic standardization of Rhodiola rosea has been carried out, including experimental field trials to optimize site conditions, planting densities, and cultivation practices [22]. The principle bioactive compounds, rosavins and salidroside, are mainly accumulated in the rhizomes. Under field conditions, Rhodiola requires 3–5 years to reach harvestable biomass, which limits its economic viability. The raw material is traditionally obtained from soil-based cultivations or wild collections, both of which face increasing constraints due to environmental pressure and land-use limitations. Growing demand for standardized raw materials has increased interest in alternative production systems. Even though hydroponic cultivation of Rhodiola has been reported, there are no data on long-term soilless cultivation. In this study, Rhodiola was cultivated for two years in an ebb-and-flow hydroponic system within an indoor vertical farming facility under controlled climatic conditions to assess the feasibility of long-term production. 

Table 2: Materials and methods for the cultivation of rhodiola for 2 years in an indoor vertical farm using hydroponic systems.

Tabelle 2: Material und Methoden für die zweijährige Kultur von Rhodiola in einer Indoor-Vertical-Farm unter Verwendung hydroponischer Systeme.

Two-year cultivation of Rhodiola was successfully in an indoor vertical farm. The dry weight per plant of roots and rhizomes from hydroponically grown plants was 1.6 times lower than that of plants cultivated outdoors, which may be attributed to reduced light intensity and limited space for rhizome development. However, the plant density in the hydroponic system (50 plants·m⁻²) was considerably higher than that in outdoor cultivation (7 plants·m⁻²). When plant density was taken into account, the yield per hectare in the hydroponic system was approximately four times higher than that of outdoor cultivation. Furthermore, as shown in Figure 1b, the content of secondary metabolites was higher in hydroponically grown plants compared to those grown outdoors.

Figure 3: a. Dry weight of roots in g/plant and t/ha cultivated in one-layer hydroponic system outdoor conditions (number of plant samples=13), b. Secondary metabolites content of plants cultivated in hydroponic system and outdoor cultivation in mg/g DW (number of plant samples=13).

Bild 3: a. Trockengewicht der Wurzeln in g/Pflanze und t/ha, kultiviert in einem einlagigen hydroponischen System und im Freilandanbau (Anzahl der Pflanzenproben=13). b. Gehalt an sekundären Metaboliten von Pflanzen aus hydroponischer und Freilandkultivierung in mg/g TM (Anzahl der Pflanzenproben=13).

Conclusion

Hydroponic systems offer a sustainable and efficient alternative for cultivating medicinal plants, particularly species where root is commercial part despite of high initial costs compared to outdoor cultivation. Evidence from the literature, supported by our experimental findings, demonstrates increased secondary metabolite accumulation and improved root integrity under hydroponic conditions. These advantages position hydroponics as a promising solution for addressing supply shortages, reducing pressure on wild populations, and enabling reliable year-round production.

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Author data

M. Sc. Pooja Suresh Gowda is a research associate at the Applied Science Center (ASC) for Smart Indoor Farming at the University of Applied Sciences Weihenstephan-Triesdorf.

Dr. Heidi Heuberger is the project leader of the working group "Kulturpflanzenvielfalt - Arznei- und Gewürzpflanzen und Pflanzengenetische Ressourcen" at the Bayrisches Landesamt für Landwirtschaft (LfL).

Prof. Dr. Heike Mempel leads the Applied Science Centre (ASC) for Smart Indoor Faming at the University of Applied Sciences Weihenstephan-Triesdorf.