Advances in the Sustainable Use of Plastics in Horticulture—Perspectives, Innovations, Opportunities, and Limitations

Abstract

The use of plastics in horticulture is reviewed with respect to its sustainability based on the traditional criteria of triple Rs (reduce, reuse, and recycling) plus a re-place strategy, taking into account possible alternatives. Hail (and insect) nets made of HD-PE, with their long-term use mostly on apple and polytunnels of LD-PE for cherry and strawberry as well as solarisation mulches (reuse), were found to be relatively sustainable solutions for their needs and are currently without alternatives. In contrast, standard black mulch, with its largest share among horticultural plastics, had the widest range of sustainable alternatives, ranging from biodegradable to spray mulch; few sustainable alternatives are available for fleeces and reflective mulches. For the third sustainable option, pilot recycling schemes were examined, such as PolieCo^TM (Italy), MAPLA^TM (Spain), and ERDE^TM (Germany); they collect 30–50% of the agricultural plastics used in their respective areas, with a successful retrieval growth rate of ca. 20% per year in the case of ERDE^TM. For the fourth new R option (replace), future sustainability perspectives for the predominant black mulch are research into and development of better, biodegradable, non-fossilbased plastics, sprayable mulch; microbes for the digestion of deployed polyolefins and, for a certain limited range (on shade tolerant crops or in high-light intensity environment), hail nets and polytunnels that are equipped/substituted by/with solar panels (“agri pv”) for the concomitant sustainable production of green renewable energy.

1. Introduction

Why Plastics?

This review for the Special Issue “Challenges for sustainable plant cultivation practices and produce supply” comes at the time of the EU single-use plastics ban, affecting items such as drinking straws and plastic shopping bags; presently, there is also the dispute about small plastic fruit packs under 1.5 kg, e.g., in France, with a focus on SDG 12 (“responsible consumption and production”). Plastic plays a dominant role in agriculture and horticulture, and it answers the following question [1,2]: “Can horticulture exist and provide year round supply of local fruit by a horticultural process called forcing (from strawberry, cherry to white asparagus), ensure fruit quality, save water and herbicides and protect the crops from insects and climate change (hail)?”.

2. Materials and Methods

2.1. Source of Information

The outcome of a literature search of the ISI Web of Science resulted in 1089 references, which were reduced to 608 references by eliminating plastics use for solely agriculture applications but without sustainability aspects; this final review uses ca. 30 references from up to mid-2023 and is based on a former related review (Blanke, 2020) [3]. This review was extended and updated (60% of references are now from the last three years) as well as integrating experience from conference participation (such as GKL) and discussion, projects; master theses; own publications; studies not yet published; visits to polyethylene (PE) and polypropylene (PP) manufacturer/plastics industry; and experience with polyolefins.

2.2. Sustainability Criteria

For the sustainability assessment of plastics use in horticulture, the traditional triple “Rs” [1,2] were applied and “replace” was added as a further alternative:

◦

Reduce: plastic type, density, and longevity/lifespan;

◦

Reuse: single-use or repeated use in the same or another year;

◦

Recycle: degree and type of contamination;

▪

plastic retrieval rate;

▪

chance of recycling;

◦

Replace: effective alternatives for the same purpose;

Fossil origin was not automatically included, as a long-lived fossil-derived plastic may be more sustainable than a single use, short-lived biodegradable plastic with; e.g., a 15-year plastic like a hail net being more sustainable than long-distance fruit imports in each of these 15 years [4].

3. Results

3.1. Hail, Insect, and Shade Nets

Use: Hail nets (

Table 1. Specifications of plastics used in agriculture and horticulture [4,5,6,7].

Plastic Specs	Main Crop	Material	Specs	Longevity	CO2e *
High structures
Hail net	Apple	HD-PE	32 µm	8–20	2
Polytunnel	Cherry	Trans LD PE	200 µm	6–12	2
Low structures; crop or ground covers
Reflective mulches	Apple	PP white		8–10 a	2–4
Mulch textile	Nurseries	PP black		8–10 a	2–4
Mulches	Veg. straw.	LD-PE black		1–2 a	2
Solarisation mulch	Bare soil	LD PE trans		1 a	2
Fleece	Vegetables	PP	16–24 µm	2 a	2–4
Asparagus	Asparagus	LD-PE	120 µm	8–10 a	2
Cultivation
Irrigation pipes	Misc.	PP black	n.a.	8–10 a	2–4
Plant pots	Misc.	PP black	n.a.	once	2–4

* values in kg CO_2e/kg of plastic.; a—years; colours represent the different type of structures.

) consist of 0.30–0.38 mm HD-PE fibres and are a costly, long-term response of fruit farmers to climate change to secure their crop and provide local market supply of apple, pear, kiwi etc. (Table 1 and

Table 2. Ecological and economic effects of plastics in horticulture/alternatives.

Plastic Specs	Main Crop	Use	Alternative
High structures
Hail net	Apple	Protect from hail, prevent sunburn, save water	No
Polytunnel	Cherry, strawberry	Prevent cherry cracking, force cherries and strawberries	No
Low structures/crop or ground covers
Reflective mulches	Apple	Produce the required fruit colouration, save mulching	Yes
Mulches	Veg. strawberry	Prevent weeds, save water and herbicides, and prevent soil erosion	Yes
Fleece	Vegetables	Protect from frost	Yes
Forcing	Asparagus	Force crop, prevent weeds, save herbicides, and prevent soil erosion	No
Cultivation
Irrigation pipes	All	Supply and save water	No
Solarisation	No	Disinfect and maintain moisture	Yes
Flower pots	Misc.	Physical plant protection	Yes
Clips	All	Tie young fruit trees/branches	Yes

). The physically strong material has to withstand hail and sometimes snow (with subsequent rain); there is currently no (e.g., biodegradable) alternative plastic, which provides such physical strength/tension for hail nets.

Sustainability aspect: Alternative, eco-friendly netting concepts include the combination with additional physiological and pathological features, such as shading and insect exclusion to reduce the amount of, e.g., insecticides against Drosophila in fully enclosed cherry orchards using a dense 1 mm mesh size (Vukovic et al., 2022) [8].

3.2. Polytunnel

Use: The use of poly(ethylene) tunnels of transparent LD-PE or HD-PE (150–250 µm; Table 1) on steel frames is to satisfy the increasing consumer demand for locally grown fruit (Figure 1) and vegetables, particularly for cherry (Figure 2) and strawberry, and to a lesser extent, raspberry, blueberry and red currants; the tunnels are also employed to provide a year-round supply of local fruit. For cherry, rain covers can prevent fruit cracking and enable picking in otherwise rainy weather, i.e., a relevant issue for fruit quality, market access, and food security. Sustainability: The alternatives are greenhouses or less sustainable, long-distance import of fruit from abroad [4].

3.3. Irrigation Pipes

Black polypropylene (PP) irrigation pipes (Figure 3) with microspinklers (Table 2) are used for drip irrigation, but also for frost protection and misting for evaporative cooling. The pipes typically remain for the duration of the orchard lifespan and are the most environmentally friendly water-saving approach in irrigation. Both the use of water and fleeces is more environmentally friendly and sustainable than the alternatives, e.g., burners or furrow irrigation, with the latter resulting in excessive water use.

3.4. Flower Pots

Use: Plant pots mostly of black PP (or PE) are widely used for the sale of flower plants, shrubs, and solitary trees (ca. 1 bil pots a year or ca. 20,000–30,000 t of PP in Germany). Sustainability: In recycling, the black colour of any plastic, including pots, prevents the near-infrared (NIR) scanning of the waste sorting machine to identify and recycle this plastic item [3,9].

Three sustainable approaches have been suggested: In the refund system, customized plant pots (Figure 4) are reused; the customer is reimbursed on their return. Pots are also re-used by the business e.g., when planting in cemeteries or public flower beds, but require expensive new dedicated potting machines and thicker pots for replicate use; however, they are beneficial for customer relations [9]. Secondly, pots from organic material such as sunflower husks (www.pottburri.de (accessed on 15 April 2023) (Figure 4) are biodegradable. However, some of these pots can be fragile (not shown) and are not destined for a potting machine. Thirdly, flower pots can be recycled if they were (a) properly disposed, (b) cleaned, and (c) not black [3,9].

3.5. Special Mulches

3.5.1. Fleeces

Use: White thin fleece spread over various vegetable crops, i.e., not directly on the soil, protects them from spring frost. The type of fleece employed is typically thin white spun polypropylene (PP) with ca. 15–20 g/m².

Sustainability: The type of fleece fiber, i.e., thin long white fibers with a 16 µm diameter, and short exposure time (2–4 weeks) in spring (March–April in the Northern hemisphere [NH]) with low UV minimize the fleece’s pre-deposition for fiber breakage and their potential of causing microplastics (Mählmann, J., pers. communication, 2022) [10]. Additionally, the relatively low contamination with soil and hence the possibility of multiple use implies a sustainable use.

3.5.2. Solarisation and Soil Disinfection e.g. against SARD

Use: Thicker transparent LD-PE (>50 µm) is used in (semi-)arid medtype climates, e.g., in strawberry cultivation in Spain, to sterilise and maintain soil moisture (Figure 5).

Sustainabilty: This is a more sustainable approach compared with chemical soil disinfectants such as poisonous chloropicrin with a large ODP or similar methods [11]; transparent PE has just been successfully substituted by sprayable polymers using the “sealing and heating approach” in Citrus orchards in the San Joaquin Valley in Southern California (Stapleton, 2021) [12].

3.5.3. Reflective White (or Silver) Mulches

Use: Reflective mulches (e.g., Extenday^TM, Lumilys^TM, BriteWhite^TM, Agritelia^TM, etc.) are woven white polypropylene (75–110 g/m²) made from fresh PP pellets; i.e., of fossil origin. They are used in greenhouses, e.g., for tomato cultivation or, more often, spread out for 2–6 weeks under the trees prior to fruit harvest (Funke et al., 2021) [13] to satisfy the market/consumer in terms of red fruit colouration, in years or areas or for difficult to colour varieties (Table 2). The main application is enhancing anthocyanin synthesis in and, to a lesser extent, red pear, cherry and red grapes. Reflective mulches are most widespread in Washington State (US), Chile, and China and to a lesser extent in South Africa, Italy, and New Zealand (Figure 6).

Sustainability aspect: In the search for sustainable alternatives to Extenday & Co., Hess et al. (2021) [14] at Klein-Altendorf (University of Bonn) developed two solutions: (a) the spreading of the reflective mulch in every other row; or (b) silver foil made from recycled aluminum. The authors’ LCA showed savings in GHG emissions in the order of 0.7–1.1 t CO_2e/ha. The question for solution (b) remains as to whether a mulch from recycled aluminum is more sustainable than plastic. An earlier work at the same location investigated the use of bright fresh wheat straw and biodegradable white paint, as used in sports arenas, for the purpose; however, both were overgrown by newly emerging grass in the orchard alleyways, which differs from the situation in the med climate without rain in August/September. The current work of Gür et al. (2023) [15] again in the temperate zone of at Klein-Altendorf (University of Bonn) and others elsewhere compared the success of reflective mulch with pneumatic partial tree defoliation for exposing the apple fruit in the autumn to direct sunlight. Partial defoliation originates from viticulture and is possibly a more sustainable approach than plastic or aluminum (Figure 7).

3.5.4. Black Mulches in Nurseries

Black woven polypropylene (PP) such as Mypex^TM (Beaulieu, Belgium) is widely used as a weed barrier/suppressor in nurseries and landscape architecture to conserve water, prevent weeds, and prevent erosion, and it can be classified as sustainable given its continuous, several year “reuse”.

3.5.5. Asparagus Black/White Mulch

Use: The early harvest of forced white Asparagus for Easter and the May bank holidays is a prime objective and rewarding business in many European countries/regions that have deep sandy soils to supply local produce at a particular time before harvesting ceases on 24 June (“Johannitag” or “St. John’s Day”). A thicker black-white LD-PE mulch (120 µm-g/m²) (Figure 8) is used to force this white Asparagus and adjust the soil temperature to a warmer or colder temperature in times of climate change for the purposes of forcing or delaying the harvest, respectively.

Sustainability: This thick, double-sided b/w PE mulch is often heavily contaminated by sandy soil adhering in its pockets, which makes it difficult to recycle. However, it is repeatedly reused over 8–10 years [13], making it a sustainable option and one that is without an alternative.

3.6. Black PE Mulch

Standard Black Mulch

Use: Black LD-PE mulch (30–50 µm/m²) is the most widely used plastic mulch, and its usage is on the increase with sometimes even thinner films, particularly in China; at least 10% of worldwide agricultural plastics are mulch films [3,4,5,6]. Whereas polytunnels increase in China, they decrease in other countries, e.g., in Germany. Due to their high molecular weight and hydrophobicity, PE films are resistant to degradation; this is an advantage for plant cultivation but a negative for their final fate on and in the soil, apart from physical tensions. Light (photo-oxidation) and UV cause PE degradation [5,6,7]. PE mulch removal from the soil at the end of a crop cycle only partially removes the undegraded parts as they can be torn apart by harvest machinery and, consequently, may be dispersed throughout the harvested area. In the past, PE mulches were recovered from the soil, disposed of in landfills, and rarely recycled or incinerated for thermal gain. To the farmer, plastic waste disposal represents an additional cost and now poses a possible problem as a source of microplastics [4,5,6].

Sustainability aspect: Black mulch is mostly a single-use plastic and can be heavily contaminated with adhering soil, making its disposal and recycling difficult, tedious, and expensive (Table 2). The use of PE films ranges from vegetable crops to strawberries (Figure 9), where plantlets are inserted into slits in the mulch. The black LD-PE mulch prevents weed growth, saves water in irrigation (Table 2), and, in strawberries, reduces the Botrytis fungal infection of the fruit.

4. Alternatives (Plastics) to Black Mulch-PE versus PLA

A wide range of papers (e.g., [7,14,15,16,17,18,19,20]) have dealt with alternative biodegradable plastics on bare soil for short cultivation cycles, but they are unsuitable for long-term covers on a rough soil surface. Their main practical and ecological advantages are that they can be left in the field (Figure 10) and/or buried in the soil to be degraded by microorganisms. Fungi, bacteria, and algae can transform these residues into carbon dioxide, methane, water, and biomass [7,16,18].

The biodegradable mulches currently in use are mainly based on starch and cellulose, polyhydroxybutyrate/valerate copolymers (PHB), and polylactic acid polymers (PLA) (Cozzolino et al.) [19], which are molecules that are susceptible to UV- and visible light-facilitated photo-oxidation or that are thermo-oxidized at high temperatures [5,6,7]. While PLA and PBB are “compostable under industrial conditions and completely degrade in the soil” (EN 13432) [21], PHB so far lacks physical strength for field use, which is an objective for the current research project ENSURE. PLA polylactic/copolyester blends, which is currently the most likely alternative, originate from a corn starch fermentation process. They are chemically synthesized and are hence not of fossil origin. But is PLA more sustainable than LD-PE, e.g., when used as black mulch in strawberry cultivation in Spain or elsewhere?

A limitation of biodegradable films is that, similarly to PE films, they are subjected to weathering and the chemical substances that are used on crops, as well as to soil microorganisms; hence, there is a risk of incomplete soil coverage for the entire crop cycle (Figure 8). Dark or transparent PE mulch used in agriculture fulfill certain criteria [19], such as the tensile strength at break or the tensile elongation at break of at least 16 MPa and 180–250%, respectively. Biodegradable films have both tensile stress and tensile elongation at a break that is lower than those of PE (Scarascia-Mugnozza et al., 2011) [7]. However, their mechanical properties fall within the range required to ensure an adequate soil coverage during the entire strawberry growing cycle. Moreover, on the basis of ecotoxicological tests, the authors demonstrated the absence of soil ecotoxicity at the end of the crop cycle after burying the material. To balance the biodegradation and physical–mechanical properties of a mulch plastic, a biodegradable mulch needs to endure until the end of the crop cycle with adequate weed control, similarly to PE mulch. In Portugal, starch-based biodegradable mulch provided such adequate ground cover and weed suppression during a strawberry autumn–winter cycle (Andrade et al. 2014) [22]. Giordano et al. (2020) [23] favoured three (out of two PEs) (Ecoflex, FKur GmbH, Willich, Germany) and eight PLA (20–40 µm/m²) biodegradable mulches in a strawberry field under the high light/UV/temperature med climate in Huelva, Spain.

4.1. PLA–Biodegradable Plastic (Mulch)—A More Sustainable Option?: “Plough the Plastic”

In practice i.e., the field, a thinner version of PLA (typically 10 µm PLA/m²) compared with PE (30–50 µm) is often used to enable faster biodegradation on and in the soil. This thinner PLA is firstly exposed to light/UV on the ground and then after ploughing to enable intimate contact with soil microbes. Two contrasting independent sustainability studies, both under a comparable Western European climate, exist in the literature. The UMSICHT study (Bertling et al., 2019) [24] is based on modeling, and many assumptions and conclusions severely contrast with the “Imulch” (“intelligent mulch” study 2021) [25]. This study is based on laboratory and sub-commissioned studies and developed new methodologies for applications such as microplastic detection (

Table 3. Amount of microplastic (“MP” < 5 mm O) retrieved by two methods, the TED GC-MS and RAMAN spectroscopy analysis after field use (Imulch, 2021) [25].

Land Use	PE (30 µm PE/m2)	PLA/PBAT (10 µm/m2)
Strawberry	<1 µg MP/g	<0.1 µg MP/g soil
Asparagus	<1 µg MP/g	<0.1 µg MP/g soil
Grass meadow	<1 µg MP/g	<0.1 µg MP/g soil

).

The 3-year “Imulch” project (2021) [25] showed, contrary to general expectations, a longer longevity of PLA/PBAT films in the field than previously found in the laboratory, where the simulated long-term exposure was speeded up in a short time. While the Bertling study (2019) [24] used 50 µm/m² PE, the thin 10 µm PLA/PBAT in the “Imulch” study started to biodegrade in Western European fields after 6 weeks but without complete degradation after 3 months the 30 µm PE showed no signs of change.

Table 3 shows that (a) microplastic residues were below detection limits and (b) were independent of the land use, contrary to the expectations and common belief. This is in line with the 2–3% residual LD-PE after field use as assumed (not measured) by Bertling et al. (2019) [24] and which is rated by experts as an overestimate.

4.2. LCA (Life Cycle Assessment) and GHG of Alternative (Biodegradable) Plastics

There are two very different approaches in the literature. In the first one, GHG emissions of ca. 1600 kg CO_2e/ha of mulch were similar for both LD-PE (30 µm) and PLA/PBAT (Imulch, 2021) [25] with the energy-expensive precursor adipic acid. The second one (Chen et al., 2023) [26]) also ends up at ca. 1600 kgCO_2e/ha for LD-PE, but 2380 kg CO_2e/ha for biodegradable PLA/PBAT mulch.

An analysis of the employed LCA shows that it includes nitrite oxide and CO₂ emissions during the cultivation phase, but it uses the thinner 10 µm LD-PE mulch. Whereas the first LCA benefits from the thermal digestion of the thicker PE, which is absent from the second study, the latter ends up in a contrary result.

4.3. Hormonal and Endocrinal Activity—Beyond Sustainability

The “Imulch” study (2021) [25] investigated hormone action that was associated with the adsorption of pesticides. The bioassays showed no endocrinal (hormonal) activity of either type of black plastic mulch, no uptake into the plant, and no adsorption and resorption of copper (used as a fungicide in organic growing) or herbicides used in conventional growing.

5. Outlook and Perspectives

5.1. Spray on Plastic Mulch from Renewable Sources

The promising research project “ABOW” (“Alternatives Beikrautmanagement im Obst- und Weinbau”) is currently still underway in a collaboration between Germany, Austria, and South Tyrol/Italy funded by the Bavarian state MAFF. Two spray nozzles concomitantly apply suspension A and suspension B (Figure 11). On mutual contact, the fluid suspensions form a solid film. The suspensions under trial are all based on renewable materials such as rapeseed oil. The target crops for this non-fossil product are fruit, grapevines, and vegetables in an another UBA project (“MuNaRo”). The hopes are high for such a sustainable product without the use of fossil sources with good biodegradation and lack of potential for microplastics; however, the fears are inconsistent soil coverage (particularly when the top soil is uneven), insufficient conservation of water soil, weeds, and the price and technology.

5.2. Microbial Plastic Digestion and Possibility of Upcycling Plastics

Another alternative is the selection and breeding of dedicated microbes for or after field use, which are able to digest PE and/or PP, i.e., in the “Imulch” and “ENSURE” project at the University of Stuttgart, headed by Prof. M. Kreutzbruck, as well as the EU Horizon 2020 project “RECOVER” (https://recover-bbi.eu/project/ assessed on 12 April 2023), which includes a biofermenter to digest the recycled plastic using microbes. In another EU horizon 2020 project MIX-UP (https://www.rwth-aachen.de/cms/root/Die-RWTH/Aktuell/Pressemitteilungen/Oktober-2020/~krbya/RWTH-erforscht-Plastikrecycling-mit-Mikr/?lidx=1 (accessed on 23 April 2023)), Prof. Lars Blank of RWTH Aachen started a project on upcycling plastics irrespective of the source (

Table 4. Recent projects on substituting or recycling agricultural (and other) plastics.

Project Acronym	Topic	P I	Website
Alternatives to (fossil-based) plastic mulches
ABOW MuNaRo	Two-component sprayable mulch	TFZ Bavaria, Austria, Italy (South Tyrol)	https://www.tfz.bayern.de/
Imulch (intelligent mulch)	PLA/PBAT as substitutes for PE mulch Umsicht, Fraunhofer	Carmen Wolf EU regional development fund ERDF	http://imulch.eu/
Projects/studies involving bacterial breakdown of plastics
ENSURE	Bacterial breeding for digestion of plastics	Marc Kreutzbruck Stuttgart-EU horizon	http://www.project-ensure.eu/
RECOVER	Biofermenter	EU horizon	https://recover-bbi.eu/project/
Upcycling of retrieved plastics
Mix-Up	Bacterial breakdown for upcycling plastics	Lars Blank, RWTH Aachen	https://www.mix-up.eu/rwth-aachen-university

).

5.3. Organic Agri PV

Trials are under way in many locations with solar panels (“agri pv”), which may then replace hail nets in some locations; similarly inorganic silicon or flexible organic solar panels (Figure 12) are on trial for use in polytunnels (B. Zimmermann, 2022 [24], pers. comm.).

5.4. Retrieval and Recycling—Part of the Solution at the End of Life

“PolieCo”, “MAPLA”, and “ERDE”—promising agricultural plastic retrieval and recycling schemes.

In Italy, “PolieCo”, the “Italian Consortium for the recycling of PE materials”, recycles ca. 34% of agricultural PE in their respective business areas (Scarascia-Mugnozza et al., 2012) [7] and also MAPLA (https://plasticosagricolas.es) in Spain.

“ERDE” (https://www.erde-recycling.de/en/; assessed on 23 April 2023) [25] is a joint venture of the recycling company RIGK (https://www.rigk.de/en/; assessed on 21 April 2023) and the international producers/traders of horticultural plastics Aspla (Spain), Barbier (France), Berry (Belgium), Daios Plastics (Greece), Reyenvas (Spain), RKW Agri (Germany), Solplast (Spain), Sotrafa (Spain), and Tencate (Austria). Local collection points and dates allow farmers to dispose of their agricultural plastics irrespective of the country of origin, producer, or trader. From 2020, this scheme now includes the difficult double-sided black and white asparagus mulch (Figure 5), and from 2021, it also includes agricultural fleeces. Since April 2022, “ERDE” (acronym for Erntekunststoffe Recycling DEutschland) included the recollection of agricultural plastic mulches; similar services are now also available for the recollection of hail nets (Figure 9) by their larger distributors such as BayWa and MaBo. All ag plastic films retrieved by “Erde” [20] such as the 26,000 t (2020), 32,668 t (2021), and 38,500 t (2022) (Figure 13) varieties, are 100% recycled and are not incinerated, with an “Umwelt certificate” being used as incentive.

6. Towards a Sustainable Use of Plastics in Horticulture and Agriculture

6.1. Hail Net (HD-PE)

(1)

Prolonged use by careful rolling up over winter and minimising physical damage over, e.g., support poles and wires;

(2)

Careful net retrieval and collection (e.g., by like “ERDE”) for recycling.

6.2. Black Mulch (PE and PP)

(1)

Short-term use of thicker, more durable PE mulch (50 µm instead of 30–40 µm), which results in a larger recovery rate of near 98% and fewer residues (Figure 8, Figure 9 and Figure 10);

(2)

Careful PE mulch retrieval and recycling using schemes such as PolieCo, MAPLA, or ERDE

(3)

Search for non-fossil alternatives with an efficient biodegradation rate.

7. Conclusions

At the moment, alternatives to hail nets (hail canons and airplanes) and fleeces do not appear to be widely feasible. In some instances, summer pruning and tree defoliation (and sometimes biostimulants) may be a suitable alternative to reflective mulches. Agri pv will add a new dimension irrespective to the sustainability of hail and shade nets, where the fruit or vegetable crops are shade-tolerant or even benefit

Overall, the sustainability of the first group of plastics in horticulture, such as hail nets, Asparagus foils, fleece, and reflective films, can be improved by better durability and longevity, proper retrieval, and plastic recycling schemes like PolieCo, MAPLA, and ERDE (

Table 5. Sustainability ranking of plastics in horticulture based on use, application, longevity, and possible alternatives (LD-PE-0.92–0.93 g/cm³; HD-PE-0.94–0.96 g/cm³).

Plastic	Use	Reuse	Alternative	Sustainability
HD-PE	Hail shade, insect net	Yes (longevity)	No
LD-PE	Polytunnel	Yes (longevity)	No
LD-PE b/w	Asparagus	Yes (longevity)	No
LD-PE transp	Solarisation	Yes	Maybe
LD-PE black	Ground mulch	No	Maybe
PP Black	Flower pots	No	Refund
PP Black	Nursery	Yes	No
PP white	Light reflection	Yes	Yes

).

The second group presented a surprise in that short-lived mulches are in demand by the grower, allowing a fast crop cycle. Some more recent studies have also indicated a longer lifespan of biodegradable mulches than required, even under field conditions of Spain (Table 5).

This review has shown many innovative projects that are underway, ranging from microbial digestion, down-cycling and upcycling to spray mulch. It remains a challenge to put the results into practice and test them under harsh field conditions for a more sustainable use of plastics in plant cultivation practices.