Nettle Cultivation Practices—From Open Field to Modern Hydroponics: A Case Study of Specialized Metabolites

Abstract

Conventional agricultural production faces numerous challenges due to the pronounced effects of climate change, particularly global warming, and drought more than ever before in history, with the primary concern being to produce adequate yields and high-quality, nutritious plant material. Likewise, people are increasingly looking for new sources of food and are becoming aware of the importance of a varied diet and its connection to health. In this sense, stinging nettle (Urtica dioica L.) stands out as a valuable species that is neglected as a food source, as it has a significant content of specialized metabolites, and thus has an extremely high potential for use both nutritionally and pharmacologically, but is still traditionally collected from natural habitats, so it can be of questionable quality and undefined chemical composition. Therefore, sustainable agricultural practices are increasingly shifting to modern hydroponic cultivation methods in greenhouses. The advantage lies in the easier management and control of a number of factors during cultivation (air temperature and relative humidity, balanced and rational fertilization, minimization of nitrate uptake, etc.), ensuring better conditions for the growth and development of nettle according to its needs. The aim of this review is to give an overview of the technology of stinging nettle cultivation in the field and to show the possibilities of cultivation with modern hydroponic techniques to obtain a final product of consistent and uniform quality, high content of specialized metabolites and significant nutritional value. Research on this topic is still sparse but will certainly increase in the future. Therefore, this review provides all the necessary data for such future studies.

Intraspecific Variability of Stinging Nettle (Urtica dioica L.)

“…With regards to the nettle, this aspect has not been studied comprehensively. The available literature on the nettle concentrates on the methods of establishing plantations using different planting densities, mineral fertilization or the influence of plantation age on the raw material quality [ 23 , 25 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Our purpose was to determine the diversity of the species both within and between populations, to select individuals useful in further work on nettle propagation and industrial cultivation.…”

“…Jankauskiené [ 28 ] claims that this parameter may be even higher; it oscillates from 0.25 to 0.91 kg DW per plant. According to the literature data, the yield of nettle may be influenced by various factors, such as genetic, environmental (type of soil, temperature, humidity, water content, irradiance, photoperiod) and agricultural factors (e.g., nutrients and their availability; cultivation technology) [ 23 , 25 , 32 ]. Our work, carried out in uniform ex situ conditions, indicates that genetic factors are crucial here.…”

“…In the view of such need, one of the first steps to be taken is to recognize the range of natural diversity of the species, which is the main source of genes indispensable for future cultivation and agrotechnical programs. So far, only a few trials with nettle that address this problem have been undertaken [ 10 , 18 , 22 , 25 , 26 ]. Some of the experiments indicate that the most important traits in determining the variation amongst the species seem to be the height of plants, the length of internodes and the number of leaves per shoot [ 27 ].…”

Nettle, a Long-Known Fiber Plant with New Perspectives

“…However, taxa belonging to Urtica dioica appear to have similar metabolite compositions and, therefore, similar pharmacological properties [84]. Modern hydroponic cultivation methods in greenhouses have also been set up for the easier management of environmental factors to improve metabolite production [101]. Nevertheless, males and females harbor different content and chemical composition of polyphenolic acids in their leaves, with the male form characterized by a higher content of these compounds [102].…”

“…Indeed, male plants would produce more leaves, more side shoots, and more rhizomes [150]. None of these possible cultivation techniques is well described, and further research is needed to identify the most suitable technique depending on the objective of the cultivation [101].…”