Phacelia tanacetifolia Benth. as a Multifunctional Plant: Support for Pollinators and Sustainable Agricultural Practices

Abstract

Phacelia tanacetifolia Benth. is a species of annual plant that has been gaining importance in recent years. Initially, it was treated as an ornamental plant and valuable only to bees. Over the years, this species has become more widely known, and many more of its advantages have been discovered. The aim of this study was to learn about the contemporary economic importance of Phacelia tanacetifolia Benth. The extraordinary, rapid increase in the plant’s biomass means that it is valued as a fodder plant and at the same time is included in the group of leaders among catch crops. It is characterized by low requirements for soil quality. The main advantage of this plant is its high resistance to drought and frost. A great advantage of this plant is its high drought resistance. It is recommended for sowing both in monoculture and in mixtures with other species. In the light of current standards and assumptions, it fits perfectly into the framework of sustainable development. It is a valuable link in the biodiversity chain, as well as support for a number of ecosystem services such as CO₂ sequestration, retention of nutrients in the soil or protection of its structure. Phacelia is seen as having great potential as a plant that provides food for a number of pollinators. The latest research also focuses on assessing the possibility of using it for energy purposes (biogas). Efforts are being made to introduce phacelia on a wider scale to eliminate crop monocultures and significantly strengthen biodiversity in a given area. Phacelia plays an important role in various agronomic systems and effectively supports the protection of the natural environment. The contribution of this species to the development of ecosystem services to date is undeniable. It should be assumed that this plant will continue to significantly support a number of activities for sustainable development.

1. Introduction

Agriculture in the 21st century faces a dual challenge: feeding a growing global population while preserving and regenerating the natural resource base on which it depends. According to the Food and Agriculture Organization (FAO), global demand for food, feed, and fiber is expected to rise by approximately 70% by 2050, while agriculture must simultaneously meet climate goals, support biodiversity, and manage natural resources sustainably [1].

Modern food systems are increasingly threatened by soil degradation, biodiversity loss, and the impacts of climate change. As a result, there is a clear shift towards sustainable, multifunctional cropping systems that integrate food production with ecosystem services such as soil health, carbon sequestration, and pollinator support [2].

Sustainable agriculture emphasizes the importance of crop diversification and the inclusion of species that contribute to soil health, support pollinators, and help mitigate climate change. Global analyses confirm that cropping diversification enhances biodiversity, improves soil health, and strengthens ecosystem services, including pollination and pest regulation [3].

One of the species gaining attention in recent years and recommended to enhance sustainable agriculture practices is Phacelia tanacetifolia Benth., an annual plant species belonging to the Hydrophyllaceae family, although some taxonomies classify it within Boraginaceae. It is native to North America and the Andes in South America and was brought to Europe in the first half of the 19th century [4,5,6]. The first activities related to the cultivation of this plant were undertaken on a small scale in gardens. Initially, it was treated as an ornamental plant and sown only in botanical gardens [7]. It was quickly discovered that in addition to its aesthetic values, this plant is very attractive to bees. Sowing this plant to provide bees with greater amounts of food is considered the beginning of its field cultivation [7]. Currently, knowledge about this species is much broader. It is known that phacelia has moderate water and soil requirements, is highly resistant to stress, and grows very dynamically. Improved knowledge of this species has contributed to its widespread popularity, especially in countries with temperate climates. Currently, interest in phacelia cultivation is strongest in Europe (where it is now widely used in sustainable farming systems), East Asia, and South America (Figure 1) [7,8]. Although official statistics from Eurostat do not report phacelia separately—grouping it instead under the category of “other annual crops harvested green”—multiple independent sources confirm a notable increase in its cultivation. A 2019 report by the Joint Research Centre (JRC) of the European Commission indicates that phacelia is among the four most commonly used catch or cover crops in countries such as France, Spain, and the Netherlands, alongside rye, mustard, and vetch [9]. In Hungary, where phacelia is grown on a commercial scale for seed production, cultivated areas have ranged from 1500 to 11,000 hectares over the past two decades, with the majority of seed destined for export to Western Europe. This trend reflects both rising demand and the economic relevance of the species in international markets [8].

Currently, in many countries, agriculture is required to use non-chemical methods to control diseases, pests, and weeds [10]. Many reports indicate that phacelia is exceptionally resistant to diseases and pests. Moreover, after harvesting, it constitutes a valuable pre-crop for most crop species. Its species distinctiveness, combined with allelopathic properties, has gained recognition among both supporters of high-volume technologies and those seeking low-volume technologies [11].

All these data indicate the high potential of phacelia in both economic and ecological dimensions, especially in the field of various ecosystem services such as pollination support, erosion control, and carbon sequestration. In light of the latest assumptions, agricultural production should pursue several goals at the same time. In addition to producing healthy food, sustainable agriculture should mitigate climate change, positively affect soil fertility, and provide clean energy [12,13,14]. The integration of this species into modern agroecosystems aligns well with these goals and represents a promising step toward the implementation of the United Nations Sustainable Development Goals (SDGs), especially those related to responsible production, climate action, and life on land [15].

The aim of this study is to verify the available knowledge on Phacelia tanacetifolia Benth. and the possibilities of its potential, multi-directional use in sustainable agriculture.

Figure 1. Geographic distribution of Phacelia tanacetifolia Benth. Source: Global Biodiversity Information Facility [16].

Figure 1. Geographic distribution of Phacelia tanacetifolia Benth. Source: Global Biodiversity Information Facility [16].

2. Materials and Methods

The manuscript was developed in accordance with the methodology presented by Mackiewicz-Walec et al. [14]. In order to obtain data for the literature review, the following bibliometric databases were comprehensively searched: PubMed, Web of Science, Scopus, AGRO, MDPI, Cambridge Journals, Taylor & Francis, Science Direct, and Springer. For the literature analysis, the following keywords were adopted: “Phacelia tanacetifolia”, phacelia + cover crops, phacelia + fertilization, phacelia + chemical composition, phacelia + energy, and phacelia + erosion. The analysis was based on papers published in English and Polish. Popular science articles and those presenting the results of research at the cellular level were excluded from the analysis. The review includes research papers published in the years 1999–2025. The articles selected for the review were assigned to the appropriate thematic groups based on which the chapters of the manuscript were built.

3. Morphology

Phacelia tanacetifolia Benth. reaches a height of 20 to 80 cm in poor and average soil and climatic conditions [4,6,17,18,19,20,21], but in conditions of good water and nutrient supply, it can grow up to 115–120 cm [22]. As reported by Walden et al. [23], the stems of the phacelia are semi-erect or erect, glandular, covered with rough hairs that protect against excessive water loss and pests. The stems are hollow and brittle, which makes them susceptible to breakage under the influence of strong winds [23]. Almost every node has first-order lateral branches 50–65 cm long, with four to six leaves. In the following stages of growth, second-order lateral branches develop, which are usually smaller and have two to three leaves. As a result, according to Cǐrlig [24], the mature plant takes on a bushy form with 15–22 branches. The leaves are alternate, sessile, pinnate, consisting of seven to eight leaflets with toothed or pinnate edges. The basal leaves are larger, asymmetric, with irregular, sharp, or obtuse edges. The flowers of the phacelia have a five-fold, bell-shaped structure and are grouped in whorls. The calyx consists of five fused sepals, and the funnel-shaped corolla, characteristic of this species, is purple-blue, with a dominant shade of purple [25] (Figure 2). The stamens are long and extend significantly beyond the corolla, which facilitates access for pollinating insects. The bipartite style of the pistil is also exposed, which is of great importance in the pollination process. At the base of the corolla is a disc-shaped nectary, protected by ten scales, which prevent access by unwanted insects, especially those that consume nectar without contributing to pollination, such as certain species of Muscidae or Formicidae. The scales also protect the nectary to a large extent from excess moisture. The scales are arranged in pairs around the stamens. Pollen, which is intensely dark blue, accumulates on the insects’ legs, giving them a characteristic dark blue or black shade [26,27].

The fruits of the phacelia are small, elliptical seed capsules containing two to four small, dark seeds (Figure 3). The seeds exhibit negative photoblasticity, which means that they germinate only in the dark [28]. According to Tiryaki and Keles [28], their germination capacity can persist in the soil for several years. The possibility of seed survival in the soil creates a risk of spreading this species, and in subsequent years, it may pose a threat to crops as a weed. The weight of a thousand seeds is about 1.8–2.4 g, and one plant can produce hundreds of thousands of seeds [29].

Phacelia is characterized by a deep tap root system, often exceeding 70 cm. At the same time, it is quite dense, thanks to which, according to many authors, it directly affects the improvement of soil structure [30,31,32,33,34].

4. Soil Requirements and Impact on Soil Properties

Phacelia has low soil requirements; it grows successfully on various types of soil, tolerates a wide range of soil pH. The optimal pH range for this plant is considered to be 6.4–8.5. However, this species tolerates an acidic pH of 4.6–5.5 [7,35]. Sowing phacelia as a catch crop or cultivated as a main crop beneficially modifies many physical properties of the soil [31,36,37]. Intercrops with phacelia contribute to improving the soil structure, arrangement of its particles, bulk density, and soil moisture content [38]. This species also has a beneficial effect on the size distribution of soil aggregates and the pore network [31]. The greatest role in improving soil properties is played by the tap root system of phacelia, reaching at least 70 cm (Figure 4). A positive effect on improving soil structure (especially on soil aggregates) after sowing phacelia as a catch crop is observed even to a depth of 40 cm [30]. Research by Harasim et al. [38] showed that catch crops with phacelia improve the soil particle size distribution, which results in a higher share of finer soil fractions. In addition, catch crops have a positive effect on bulk density and soil compaction. The same authors noted that catch crops also stimulated enzymatic activity—in particular, urease and dehydrogenase. An important advantage of phacelia is the ability to easily manage the plant mass and leave it in the form of mulch for the winter [39,40]. The stems (hollow inside) and leaves of this species, especially after freezing, become brittle and can be easily mixed with the topsoil. This method is currently recommended as one of the best soil protections for the winter [23,41,42].

5. Agronomic Management—Cultivation Recommendations

Phacelia is considered a species that is not very demanding in terms of agrotechnics. It is grown both as a main crop and as a catch crop [18]. Literature reports indicate that cultivation as a main crop is much less popular than catch crops or intercrops [7]. It has low nutritional requirements. Grown as a main crop, for fodder or seeds, it needs approx. 40–80 kg N, 60–70 kg P₂O₅, and 80–90 kg K₂O per hectare. In the secondary crop, both for catch crops with the intention of ploughing in and for energy purposes, it is recommended to introduce only approx. 40 kg N/ha to the soil. The remaining components should come from the pool unused by the main crop [7,43,44]. Svensson et al. [43] even believe that the use of a higher dose of nitrogen per catch crop than 40 kg is economically unjustified. Phacelia has a short vegetation period of 90–100 days. For this reason, it can be sown even three to four times per season [45]. The sowing rate for seed plantations is 9–12 kg of seeds/ha. Phacelia grown as a catch crop in pure sowing requires sowing 14–18 kg of seeds/ha. This species, intended as a catch crop, works very well in mixtures with other plants such as Persian clover, buckwheat, oilseed radish, field vetch, or rye [43,46]. In such use, the sowing rate should be reduced accordingly. Phacelia sown in a mixture with rape and peas at a rate of 6 kg/ha is shown in Figure 5. This mixture effectively protects the field from weeds and nutrient loss. However, as Żuk-Gołaszewska et al. [47] report, growing autumn-sown crops can be significantly affected by water deficits. It is recommended to place the seeds at a spacing of 12.5 cm at a depth of a maximum of 1.5–2 cm and cover them well with soil [44]. For this purpose, both classic seed drills and cultivation-sowing units are used, as well as special seed drills dedicated to catch crops. The possibility of quick, direct sowing of phacelia when stubble management after the main crop is also its great advantage as a catch crop [7]. Phacelia’s germination capacity is high and usually amounts to 84–92%, and the germination energy is 1–3 days [5,24]. The plant’s high resistance to stress conditions allows germination to occur even with low soil moisture. In the later stages of growth, the plant tolerates periods of drought well [7]. Phacelia tanacetifolia Benth. exhibits moderate tolerance to water stress during both the germination and vegetative growth stages. Recent agronomic studies have reported that phacelia exhibits high root length density and root area, traits that are typically associated with drought-adapted cover crops. This characteristic facilitates efficient soil moisture extraction from upper soil layers [36]. The species germinates in field conditions at temperatures from 8 degrees [24]. According to Kosolapov et al. [11], it thrives in sunny areas and in partial shade under tree crowns. It withstands frosts down to −10 °C [7]. However, Haberle et al. [48] point out a disadvantage, which is the poor resistance of this species to frost during the flowering period. Phacelia is characterized by a very rapid increase in biomass. It can reach its full development cycle in as little as 45–50 days [49]. The amount of biomass obtained is strongly dependent on the period of the year in which the seeds were sown, climatic conditions, and soil type [50].

Dynamic growth means that it can quickly shade the soil and effectively drown out weeds. It has been proven that the use of herbicides in phacelia crops is not always justified. With intensive development, this plant effectively competes with weeds, and the application of herbicides is unnecessary [51]. Phacelia as a catch crop contributes to a strong reduction in weed infestation [52,53,54]. The results of Büchi et al. [55] show that the cultivation of cover crops (including phacelia) before corn is a promising method supporting weed control. Both mowing and incorporating cover crops into the soil effectively reduce the number of weed species and their diaspores. As reported by Tursun et al. [56], phacelia, mowed or mixed with soil as a cover crop, has proven to be more effective in protecting apricot orchards than herbicides or mechanical weed control. In the competition of the blue phacelia with weeds, the essential oils secreted by it are extremely helpful. Thanks to this mechanism, phacelia eliminates almost 100% of some species [57]. Currently, many reports indicate the need to include catch crops in crop rotation. This results from the many obligations and standards imposed on modern agriculture [47,58]. Phacelia, in at least several aspects, suits the assumptions of modern agricultural policy [59]. One of the most important tasks of these policies is the sustainable management of nutrients. Phacelia cultivated as a catch crop effectively retains nutrients through biological sorption. The nutrients accumulated in the biomass are largely not lost through leaching [43,44,47]. This species is a valuable complement to crop rotation due to its botanical distinctiveness [8,29]. The cultivation of phacelia is particularly beneficial on farms with simplified rotation; the introduction of this plant eliminates the effects of an excessive share of cereals in the sowing. It is reported that when used in crop rotation, it has, among other things, phytosanitary effects—it limits the occurrence of some pathogens in the soil (non-chemical method). It is primarily useful in crop rotation with frequent cultivation of winter rape, as it limits the occurrence of beet cyst nematode (Heterodera schachtii Schmidt), which multiplies intensively in the presence of brassica plants [60,61]. Phacelia cultivation as a cover crop has been shown to exhibit clear allelopathic effects, primarily due to phenolic compounds released from decomposing plant residues. A recent glasshouse experiment using aqueous extracts from roots, stems, leaves, and flowers demonstrated that even at 10% concentration, phacelia significantly inhibited germination and early seedling growth of triticale (×Triticosecale), with leaf and flower extracts being the most phytotoxic. In orchard systems, particularly apple and peach, phacelia mulch has been observed to reduce soil fatigue symptoms by lowering phytotoxic phenolic accumulation and suppressing soil-borne fungal pathogens. These allelopathic effects are both concentration- and time-dependent: longer cover periods (>60 days) and higher residue levels result in greater inhibition of competing plant growth, suggesting cumulative suppression potential useful in integrated weed management [62,63]. Although phacelia’s allelopathic impact is relatively mild compared to strongly phytotoxic species (e.g., Juglans regia), its contribution to soil restoration and weed suppression in diversified cropping systems is agronomically valuable. Phacelia is also considered relatively resistant to diseases [7,8,18]. However, Stępniewska-Jarosz et al. [64] list Botrytis cinerea, Sclerotinia sclerotiorum, and Fusarium spp. among the most important pathogens causing diseases in phacelia. However, further field-based studies, particularly those quantifying interspecific competition coefficients, allelopathic indices, and nutrient scavenging efficiency, are needed to better define its role in sustainable crop production systems.

The vigorous and rapid growth of phacelia allows for the production of a large mass of organic matter in a short period of time [45]. Grown as a catch crop, it can compensate for a dose of manure of up to 24 tons [65]. Importantly, the components accumulated in the biomass usually constitute a pool of those most exposed to losses [43]. At the same time, phacelia sequesters undesirable CO₂ in the atmosphere, which additionally increases the balance of positive ecosystem activities of this plant [59].

Many reports indicate a beneficial effect on the yield of successive plants after phacelia cultivation [47]. The presented data are generally not very precise, and this phenomenon requires further research. In the study by Siwek et al. [66], a phacelia catch crop increased leek yields by 15.8% and parsley by as much as 197%. However, the catch crop did not affect the chemical composition of the above-mentioned vegetables [66]. The beneficial effect of the mulched phacelia catch crop is also reported by Kęsik et al. [67], who found an increase in the yield of onion and carrot.

6. The Role of Phacelia in the Aspect of Beekeeping

Currently, phacelia is most appreciated primarily as a honey plant [7,8]. Many reports indicate that, in terms of benefits for pollinating insects, phacelia is among the world’s leading honey plants. It is one of the 20 most efficient species in this respect. In European countries, it is included in an even tighter group of the most valuable plants for pollinators and is often placed near the “podium” [5,8]. One of the main reasons for the popularity of phacelia among beekeepers is its very long flowering time of 40–55 days, and its length is slightly dependent on the weather [68,69]. Petanidou [70] reports that irrigation of phacelia increases nectar production and extends the flowering period. Flowers in the inflorescence open gradually, and the last ones open while the fruit is forming and ripening [68,69]. This feature, however, is a serious disadvantage of this plant when harvested for seeds, as the presence of still-forming inflorescences may increase the moisture content of the harvested seeds [7]. Phacelia secretes nectar regardless of the weather and is eagerly visited by pollinators, even after dark [26] (Figure 6 and Figure 7). The amount of nectar is 1.0–4.5 mg/flower, with an average sugar concentration of 28% [24]. This enables the plant to provide nectar for honeybees, which equates to a honey production of 600–1200 kg/ha [24,71].

The second equally valuable product is bee pollen produced from phacelia pollen. The pollen consists of proteins, lipids, sterols, numerous minerals, and biogenic elements such as carbon and nitrogen. The concentration of protein in phacelia pollen is comparable to that of rapeseed flowers and amounts on average to approximately 27% [72,73]. The detailed content of amino acids in the phacelia inflorescence is given by Vergun et al. [74] (Figure 8). Phacelia pollen is considered a noteworthy source of minerals. Their concentration is one of the highest among plants used by honeybees. Pollen granules collected from foragers returning to the hive are particularly rich in phosphorus, potassium, and calcium. All this makes bee pollen from phacelia flowers considered a valuable natural dietary supplement [75,76].

In beekeeping, a common recommended and positively reviewed practice is the intentional sowing of Phacelia tanacetifolia Benth. in monoculture. This is associated with ensuring sufficiently high food resources for bees while simultaneously obtaining high levels of honey [22]. Sprague et al. [77] report that phacelia grown to enrich the range of melliferous plants is not always eagerly visited by bees and other pollinators. Studies conducted on honeybees have shown that they may not use intentionally sown phacelia under agri-environmental schemes (AES). The cited authors indicate the need for a more thorough assessment of the use of resources dedicated to honeybees and other pollinators under AES. Phacelia is recommended for annual mixtures for flower strips. Studies by Kowalska et al. [78] also confirm the possibility of using phacelia in the second year of maintaining these areas, where only phacelia with incarnate clover (among the plants sown the previous year) is able to produce seeds and repopulate the area designated for this purpose. Phacelia sown in this way accounted for 6.73 to even 33.10% of the total pool of flowering plants of the flower strip in May and June, respectively. Nevertheless, uncontrolled sowing of seeds is a potential risk that phacelia may pose to native species [79,80].

7. Suitability for Livestock

One of the important uses of phacelia is its role as a fodder plant [50,81]. This plant is used as an alternative source of fodder in animal production, especially in Turkey. According to Dumanoğlu [81], phacelia green fodder grown for feeding purposes can constitute a full-value feed for ruminants. Due to its short vegetation period, Phacelia tanacetifolia Benth. allows for the production of large amounts of feed [45]. Its yield depends, to a great extent, on soil and climatic conditions. Ates et al. [82] report the possibility of obtaining a yield of green mass of phacelia at the level of over 60 tons/ha FM (9.87 t/ha DM). Pruszyński and Mrówczyński [7] report that the yield of phacelia green fodder in Central European conditions is so unattractive in terms of quantity that this species is replaced by more efficient plants, e.g., grass or clover. They also emphasize that this plant can be a good source of feed throughout the year in Turkey. The nutritional value of feed obtained from phacelia is comparable to alfalfa [83]. The exact chemical composition of this plant is given in

Table 1. Chemical composition of phacelia (budding phase experimental conditions [32], field experiments, Akmanlar, Türkiye [36]; high tunnel experiment, Cracow, Poland [44]; field experiments, Mochelek, Poland [82]; field experiments-Türkiye [83]; microplot experiment, National Botanical Garden, Chişinău, Republic of Moldova [84]; field experiments, northwestern Alberta, Canada).

Ingredient	Unit	Content	Source
Dry matter (DM)	%	11.8	[36]
Acid detergent fiber (ADF)	g/kg	346.3–388.0	[32,82,84]
Neutral detergent fiber (NDF)		425.1–553.0
Total digestible nutrients (TDN)		588.0–601.2
Acid detergent lignin (ADL)		224.3–237.0
Crude protein (CP)	g/kg	132.2–170.0	[82,83,84]
Crude fiber (CF)		324.0	[83]
Celulose		303.0
Crude ash		93.8–104.7	[32,83]
Carbon (C)	g/kg	499.0	[83]
Nitrogen (N)		23.7–27.9	[44,83,84]
Phosphorus (P)		4.9–5.5	[44,83,84]
Potassium (K)		38.8–39.6	[44,83,84]
Calcium (Ca)		16.3–29.0	[44,83,84]
Magnesium (Mg)		2.0–3.9	[82,84]
Sodium (Na)		2.0–3.1	[36,84]
Sulfur (S)		2.3	[36]
Boron (B)	mg/kg	26.8	[36]
Copper (Cu)		7.57
Iron (Fe)		158.0
Zink (Zn)		24.1
Manganese (Mn)		27.9
Titanium (Ti)		3.44
Biomethane potential	l/kg	324.0	[83]
Digestible energy	MJ/kg	12.05	[83]
Metabolizable energy		9.89

. One of the important features of phacelia is the high proportion of leaves, reaching 56.4% of the entire plant. Thanks to this, the plant is eagerly consumed by animals even later in the growing season [83]. Green fodder from phacelia is considered rich in nutrients; however, due to the possible high concentration of nitrates, it disqualifies the use of phacelia for direct feeding to beef cattle [84]. On the other hand, Jasińska and Kotecki [18] report a positive effect of phacelia on the fatty acid profile in cow’s milk. Furthermore, according to the aforementioned authors, due to its crude protein content and high digestibility, this species should be used in ruminant nutrition.

Research on the use of phacelia as a substrate for the production of protein concentrates should be considered developmental. Catch crops, which include a phacelia monoculture, can be a real option for obtaining products rich in high-value protein and provide farmers with additional income from catch crop cultivation. Phacelia grown for this purpose achieves a 25% higher dry matter yield and protein yield by as much as 70% compared to, for example, buckwheat [85].

8. The Healing Role of Phacelia

Phacelia is an increasingly popular subject of interest in terms of its medicinal use. Beneficial effects on health have been proven for bioactive substances isolated from whole plants, pollen, and those contained in phacelia honey [86,87,88,89].

Due to the fact that phacelia cultivation is becoming more and more common around the world, it is possible to obtain larger amounts of this type of pollen, which translates into its availability on the market and the possibility of multi-directional use [87]. For the consumer, it is a source of over 200 nutrients, including almost all vitamins (especially C, A, E, and B vitamins), micro- and macro-elements (iron, cobalt, manganese, copper, calcium, sodium, potassium, phosphorus), and also some plant hormones. However, it should be emphasized that the bioavailability and stability of these nutrients during digestion may be limited. Studies on bee pollen have shown that the average bioavailability of total phenolic compounds and flavonoids was approximately 25% and 31%, respectively. This was associated with a decrease in antioxidant capacity after gastrointestinal digestion, and of the 35 phytochemicals, phenylamides were the most digestible [90]. Pollen exhibits limited nutrient absorption due to its complex outer cell wall, which is not readily digested by monogastric species such as bees and humans. For example, the hard exine wall of pollen can limit nutrient release, reducing bioavailability by up to 50% in untreated pollen—although processing methods such as milling, enzymatic hydrolysis, fermentation, or wall disruption can increase digestibility from 62% to 85–98% [91]. Phacelia pollen is a rich source of bioactive phenolic compounds, especially flavonoid glycosides and phenolamides, known also as hydroxycinnamic acid amides or phenylamides [87]. As reported by Sheykhmagomedova et al. [88], the use of phenolic compounds as agents preventing the risk of developing various cardiovascular diseases, as well as the prospect of creating modern, highly effective drugs based on them, is currently the subject of practical application [88]. Phacelia can be used for cost-efficient extraction of bioactive compounds, including N′,N′′,N′′′-tri-p-coumaroylspermidine with proven cytoprotective, antiviral, and antidepressant potential. It has also been shown that in conditions of twin hyperlipidemia, therapeutic and prophylactic administration of Phacelia tanacetifolia phytocomplex at a dose of 300 mg/kg helps to normalize lipid metabolism in blood serum [87,88].

It has been proven that phacelia honey has medicinal properties, such as antibacterial, antifungal, and anti-inflammatory properties, and it is therefore used, in particular, in the treatment of inflammation of the mouth and throat. It is an excellent source of energy, supporting the healing and convalescence processes. Due to the high content of easily digestible simple sugars, it is also effective in the regeneration of the body after mental and physical exertion [86,92,93,94,95].

9. Reclamation of Degraded Areas and Ecosystem Services

Plants grown as catch crops provide a number of ecosystem services, including CO₂ binding. As a result, plants grown as catch crops directly contribute to improving the climate [52,58]. Scientific studies in this area are scarce and require further detailed research. Carbon taken from the atmosphere for the purposes of building biomass goes directly to the soil and forms the basis for the formation of humus compounds. This, in turn, positively affects soil fertility [96,97]. In the case of phacelia catch crops, despite being harvested for feed or biogas, 25–35% of the grown biomass still remains in the soil in the form of crop residues and roots [98]. This is an important source of nutrients (especially phosphorus) for subsequent crops. Phacelia has a unique predisposition to accumulate phosphorus even in soils poor in this element. This is facilitated by an extensive root system that penetrates the soil and absorbs nutrients from deeper layers [47].

The cultivation of catch crops to a great extent prevents water pollution with nutrients from agricultural and horticultural production, especially nitrates. However, the addition of fresh plant material to the soil in late autumn or winter, through the abrupt termination of cover crop growth resulting from tillage or exposure to freezing temperatures, may constitute a risk factor for nitrous oxide emissions. This is facilitated by the simultaneous occurrence of moist soil conditions. Nevertheless, the risk of dinitrogen oxide contamination is over 2.5 times lower in the case of phacelia than, for example, oil radish [52].

Cover crops, including phacelia, are very effective in erosion control and counteracting soil environment degradation [31,46,81,99]. Kumar et al. [100] report that the protective effect of phacelia is strongly dependent on the autumn sowing date. It is possible to reduce nitrogen leaching by about 47 kg N/ha. The longer the date is delayed, the weaker the protective effects are. Soil protection decreases with the decomposition of plant biomass. Over time, the effectiveness of reducing nitrate leaching decreases significantly. Phacelia is also used to prevent water erosion [81]. It is most effective during vegetation time. At the beginning of winter, when cover crops freeze, above-ground biomass becomes less effective in protecting the soil from this phenomenon [46]. On the other hand, phacelia used as a catch crop improves water management through its effective water retention. The use of water by this species is considered very rational [101]. Phacelia thrives in soils heavily contaminated with heavy metals. It is recommended as a plant with phytoremediation properties. Both green fodder and residue from crops in contaminated areas do not require additional treatment related to the removal of metals and can be used for direct fertilization [102]. The use of phacelia for the biological reclamation of areas after sulfur extraction brings good results [103]. As reported by Klimont et al. [104], introducing this species to post-mining areas additionally fertilized with municipal sewage sludge is rational, because it allows for the simultaneous utilization of post-industrial and domestic waste, allows for the reconstruction of plant cover in devastated sites as well as obtaining bee food (nectar, pollen) and has a positive impact on the aesthetics of the surroundings. In addition, the cultivation of phacelia in such areas has a beneficial effect on the chemical properties of the substrate by increasing the resources of organic matter and available nutrients. Phacelia can be successfully used in the process of removing oil-derived pollutants from the soil. This species also supports the development of biological life and the population of microorganisms, which significantly improves the efficiency of the purification process [105].

10. Energy Generation

Phacelia is increasingly indicated as a typical cover crop with the possibility of using it for energy purposes in various parts of the world (Europe, Australia, North America) [106]. The subject of interest is fresh biomass or ensiled biomass intended for biogas production [43,59,107]. The average methane content in biogas from phacelia fermentation is one of the highest among many species of annual plants and can range from 58.8 to 63.6% [107]. Svensson et al. [43] determined the possibility of obtaining methane from phacelia biomass from monoculture at the level of 749 m³/ha and its mixture with buckwheat (40% share of phacelia) at the level of 704–755 m³/ha. The same authors emphasize that this is a good way to use soil nitrogen resources after harvesting the main crop. They also report that both plants not fertilized during growth and fertilized with 40 kg N/ha produce such large amounts of biomass that the entire biogas production process is profitable. It is also worth mentioning that after harvesting the catch crop with phacelia, 25–35% of the components still remain in the soil in the form of biomass from crop residues and roots [98]. After fermentation, the residues are returned to the fields and introduce a number of nutrients [59]. The digestate can be dosed onto the field based on the current soil fertility, which allows for more precise fertilization than in the case of direct ploughing into the grown biomass.

11. Directions for Further Research on Phacelia tanacetifolia Benth.

Based on the analysis of available literature, the authors’ own research, and expert opinions, it is possible to suggest a certain research area related to phacelia and its impact on sustainable agricultural practices. Research on the correlation between phacelia cover crops and ecosystem services such as CO₂ sequestration, nutrient biosorption, and a climate-neutral energy source (biogas) should be continued and expanded [43,59,106]. Literature reports indicate the need to improve the nutritional value of phacelia forage intended for direct feeding. No studies were found in the available literature regarding the energy inputs associated with phacelia cultivation and its impact on the carbon footprint. Many practitioners point to the need to develop technology that would ensure the longest possible flowering of phacelia in the same area—varying sowing dates can make phacelia bloom almost throughout the entire season of pollinator activity [25,80]. The authors’ own previous, multi-year research on fallow land suggests that it would also be worthwhile to conduct research on the selection of species accompanying phacelia in mixtures intended for flower meadows, flower strips, and perhaps also fallow land in the future [12,13].

12. Conclusions

Currently, phacelia has attracted great interest among researchers. Its popularity is not waning among farmers either. This is a direct result of its numerous possible applications. In countries with a dry climate, phacelia is used in animal feed. Analysis of cultivated areas indicates that phacelia is used for direct feeding only in small quantities. In Central Europe, it is more appreciated as a honey plant and a source of valuable biomass for soil regeneration. The above-average nutritional value of phacelia pollen prompts researchers to determine an easy and effective way to support not only the honeybee breeding but also a number of other pollinators. Phacelia’s lush and rapid growth, also in the autumn period, means that it is increasingly present in cultivated fields as a catch crop. The noted increase in interest in its cultivation is related to its use as a catch crop. Its moderate agrotechnical requirements, low seed cost, the possibility of sowing seeds after simplified cultivation, and achieving a good effect of improving soil fertility at a low cost in a short time make phacelia have a well-established position as a catch crop. The reports indicating the possibility of further improving its potential by introducing genes from wild-growing lines of this plant should be considered promising. However, it should be remembered that such activities may encounter limitations typical of interspecific crosses, such as linkage drag or differences in ploidy levels. As indicated by Bohra et al. [108], practical implementation requires further field verification and assessment of legal conditions. According to many scientists, there is a great chance of obtaining even taller plants of this species, which will result in greater efficiency of feed, energy, or catch crop biomass. All previous scientific achievements, largely already used in practice, indicate the great potential of phacelia. According to the latest guidelines, modern agriculture should pursue economic, social, and pro-environmental goals. In this respect, phacelia can play a valuable role in the implementation of sustainable development goals.