Strawberry tunnels: which shelter to choose?

Choosing a shelter for strawberry growing is not a catalogue decision. It is a structural decision that commits the farm for ten to twenty years: it determines the crop systems available, the margins for manoeuvre on ventilation and shading, the uncovering schedule, and ultimately the profitability of every season. Between the removable low tunnel, the multi-span structure with straight sides, and the heated greenhouse, the agronomic and economic logic is not the same — and a sizing mistake is paid for over several campaigns.

The protected cropping market has become considerably more structured over the past twenty years. Professional strawberry growers targeting early production, soilless systems or ever-bearing varieties have requirements that entry-level structures cannot meet. On the other hand, a well-managed low tunnel remains a highly effective tool for diversified farms seeking to secure two to three extra weeks of production without tying up significant capital.

This article compares the three main shelter families, examines the agronomic criteria guiding the choice — covering film, ventilation, seasonal management schedule, compatible crop system — and sets out the basis for realistic economic reasoning. The variables are numerous: what follows is a decision-making framework, not a prescription.

Your strawberry shelter has been in place for three years — but do you really know how to manage it?

Do you know exactly at what humidity threshold inside the tunnel you need to open the vents to avoid triggering a Botrytis epidemic during flowering? How do you adapt the uncovering protocol if a cold snap is forecast when your flowers are already open? And if you are considering switching to suspended gutters, can your current structure bear the additional load?

These questions cannot be answered by a generic technical fact sheet. Fraisibot advises you in real time on your strawberry crop, taking into account your crop system, your variety and the current phenological stage.

Low tunnel, multi-span, heated greenhouse: three different logics

Strawberry shelters fall into three main families. Their fundamental difference lies not only in dimensions or cost — it lies in the production logic they enable or constrain.

The removable low tunnel

The low tunnel — also called a forcing tunnel or caterpillar tunnel — is the most common structure on small and medium-sized farms. Its standard width ranges from 4 to 5 metres, its ridge height is around 2.20 to 2.30 metres with a straight-side height of 0.80 to 1.00 metre. The hoops are made of galvanised steel, the covering film of 200-micron thermal or diffuse polyethylene.

Its main advantage is operational flexibility. The structure can be assembled and dismantled relatively quickly, moved from one plot to another as rotations require, and it needs no foundations or planning permission. For a diversified farm that rotates strawberries through its cropping plan, it is a well-suited tool.

Ventilation is managed by sliding the film laterally or by opening the end walls. This is simple but imprecise: the adjustment range is limited, and daily opening and closing requires significant labour over long tunnel runs. The internal air volume is low, which reduces thermal inertia and exposes the crop to wide day-to-night temperature swings.

In thermal terms, a 200-micron plastic tunnel retains +3 to +6°C above outside temperature at night. Adding a non-woven fleece type P17 close to the plants provides an additional gain of -2 to -3°C on minimum temperatures — which can make the difference during a spring frost of -1 to -3°C at the flowering stage.

The multi-span structure with straight sides

The multi-span is the reference intensive production structure for professional strawberry growers. It is characterised by spans of 6 to 12 metres wide, straight sides of 1.65 to 1.90 metres, high-strength TO95 oval-tube hoops and aluminium gutters. The ridge height often exceeds 3 metres on the largest models.

This high air volume gives it significantly superior thermal inertia compared to the low tunnel: temperature variations are dampened, daytime heat spikes are attenuated, and nights are better retained. Ventilation can be motorised — ridge openings, lateral roll-up, fans — enabling precise climate management without deploying labour for every weather change.

The multi-span is compatible with all crop systems: in-ground on ridges, soilless in suspended gutters with integrated reinforced supports. It is the only structure that allows the passage of a tractor or spray equipment without a cab, thanks to the straight-side height. It is insurable (certified to greenhouse standards depending on the region) and eligible for certain agricultural financing schemes.

Its constraints are real: the investment is incomparable to a low tunnel, the installation is fixed for one to two decades, and depending on the covered area, planning permission may be required.

The heated greenhouse

The heated greenhouse — glass or polycarbonate with forced-air or hot-water heating — is reserved for ultra-early production strategies or continuous ever-bearing production. It offers maximum thermal control: winter night minimums are managed, plantings can take place in autumn or winter, and first harvests can be brought forward to as early as March.

Its running cost is its main drawback: the energy bill structurally increases variable costs, and profitability depends closely on commercial positioning — premium circuits, catering, early-season niche markets — and the selling price achieved at the start of the season.

The covering film: an agronomic choice as much as a technical one

The covering film is often treated as a secondary variable — an accessory to the choice of structure. This is a mistake. It directly determines thermal management inside the shelter, the risk of leaf scorch, the intensity of solar radiation and, ultimately, the health quality of the fruit.

Clear film vs diffuse film

Clear film allows direct solar radiation to pass through. Under strong sunlight, it creates significant temperature peaks during the day and generates shadows cast by the hoops — zones of heterogeneous light that can affect the uniformity of fruit colouring.

Diffuse film (90% light diffusion) eliminates cast shadows and distributes radiation uniformly across the entire cultivated surface. It attenuates thermal peaks, reduces the risk of solar scorch on fruit — particularly for sensitive varieties such as Glorielle or Florence — and improves working conditions in summer. It is particularly recommended in high-sunshine areas and for soilless gutter systems, where planting density amplifies the thermal mass effect.

Precise comparative agronomic data on the impact of diffuse vs clear film (Brix, fruit size, colour) are not well documented in French public technical references. What practitioners observe does converge, however: diffuse film reduces the need to whitewash films during heatwaves and improves ripening uniformity. The choice between the two should be reasoned according to the climatic zone, the orientation of the structure and the main production period.

Service life and replacement

A professional 200-micron 7-layer UV-stabilised film carries a 5-season guarantee, with an observed service life of 6 to 8 years under normal operating and maintenance conditions. This replacement must be factored into the cash-flow plan from the initial investment — it is a significant recurring cost per hectare.

Uncovering, ventilation and climate management: the seasonal schedule

This is the topic that shelter manufacturers never address — because it is not their job. Yet the quality of seasonal management often makes more difference to the economic outcome than the structure itself.

The logic of seasonal uncovering

The uncovering schedule does not follow a fixed calendar. It follows a dynamic logic that combines the phenological stage of the plants, local weather forecasts and varietal sensitivity. The general strategy for unheated tunnels is to close shelters in autumn and early spring to accumulate heat hours and activate vegetative development, to protect flowers — which freeze at just -1°C — during at-risk nights, and to ventilate heavily in summer to avoid overheating and humidity build-up.

In practice, the decision to open or close is not made on a date but on a combination of signals: expected night-time temperature, phenological stage (vegetative, flowering, fruit set, fruiting), humidity inside the shelter, sanitary status of the plot.

The ventilation / Botrytis tension

Botrytis prevention in strawberry growing is inseparable from ventilation management inside the shelter. Botrytis cinerea develops in a window of 15 to 25°C combined with relative humidity above 75% — conditions that frequently occur inside tunnels in spring.

Ventilation is the first prevention lever: opening the sides when temperatures are mild allows stagnant humidity to escape, dries plant tissue and brings the RH below the critical threshold. This ventilation also promotes the work of pollinating insects. In parallel, overhead irrigation on flowers and fruit must be avoided: free water on tissue is a direct triggering factor for the fungus.

But here lies the fundamental tension: ventilating at flowering also exposes flowers to night-time temperature swings. A cold drop to -1°C on an open flower means compromised fruit set. Managing ventilation at the flowering stage requires permanently balancing the Botrytis risk against the frost risk — and the answer depends on the variety, the exposure, and the season.

Fraisibot answers your agronomic questions in real time — including the most delicate ventilation decisions, stage by stage and according to your pedoclimatic context.

Summer shading and Drosophila suzukii

In summer, the challenge reverses: ventilation must be maximised to protect fruit from heat stress. Above 30°C inside the tunnel, fruit flavour quality deteriorates, post-harvest shelf life drops and the risk of flower abortion increases in ever-bearing varieties. Documented solutions include diffuse film, lateral shade netting and targeted film whitewashing during heatwave episodes.

Opening shelters in summer also requires particular vigilance regarding pest management in strawberry crops under cover: Drosophila suzukii — a fly that lays eggs in undamaged fruit — exploits unprotected openings to enter the tunnel. Installing insect-proof mosquito-mesh netting over end walls and lateral vents is an essential preventive measure as soon as temperatures allow prolonged opening.

Crop systems: what the shelter makes possible

The type of structure directly determines the crop systems available — and therefore the achievable yields and intensification levels.

In-ground on ridges

This is the most common system under low tunnels. The recommended density in a double staggered row is 55,000 to 65,000 plants per hectare, with a 25 cm spacing on the row and 120 cm between ridges. This system remains compatible with crop rotation, limits equipment investment and suits diversified farms well.

Its main risk is soil-borne disease pressure: Verticillium wilt, Phytophthora cactorum and other soil pathogens accumulate with frequent returns of strawberry on the same plot. The duration of the crop cycle and rotation management strongly determine the sanitary pressure over the long term.

Soilless in suspended gutters

Gutter cultivation is the system that makes the best use of a multi-span structure with reinforced support-equipped straight sides. Density rises to 75,000 to 110,000 plants per hectare, with 20 cm plant spacing on the row and gutters spaced 80 to 110 cm apart.

The most commonly used substrates combine blonde peat (60-70%), coco fibre (20-30%) and perlite or vegetal compost (~10%). This blend optimises water retention, root aeration and drainage — critical parameters when fertirrigation manages all of the plant's nutrition.

The advantages of the soilless system are multiple and measurable. Yields reach 40 to 70 tonnes per hectare versus 20 to 40 t/ha for in-ground tunnel production — roughly double the productive potential. The elimination of soil-borne diseases removes a significant share of the sanitary pressure. And the ergonomics of picking in a standing position reduce the physical strain of a task that accounts for 60 to 70% of variable costs on the farm — a direct labour competitiveness lever.

Substrate on the ground

Bags or pots on the ground represent an intermediate system, compatible with taller low tunnels or lightweight multi-spans. The substrate investment is lower than for suspended gutters, sanitary control is better than in-ground, but harvesting ergonomics remain constraining. It is often a transition step for farms testing soilless production before investing in a structure adapted for gutters.

Economic trade-off: reasoning the investment over time

No available comparative guide addresses this angle with reference data. Yet it is the central question for a professional grower who must choose between three investment levels with radically different economic logics.

Investment ranges

The reference figures from technical institutes are as follows. Installing a single-span plastic tunnel represents an investment of €15,000 to €30,000/ha, excluding plants. For equipped multi-span structures with automated ventilation, investment rises to between €100,000 and €250,000/ha. To these structural costs must be added the purchase of planting material: from €9,000 to €50,000/ha depending on plant technology — cold-stored bare-root, plug plants or tray plants.

The gap between a low tunnel and a fully equipped multi-span therefore represents a factor of 5 to 10 in initial investment. This ratio means nothing on its own: it must be cross-referenced with achievable yields and margins per system.

Reasoning by margin

In light tunnel production with direct sales or organic farming, turnover runs at around €45,000 to €70,000/ha, with an estimated gross margin of between €20,000 and €60,000/ha. This is an achievable outcome with limited structural investment.

In soilless production under multi-span tunnels, the potential changes scale: turnover can reach €120,000 to €250,000/ha, with gross margin of between €30,000 and €100,000/ha. The investment is heavy, but the level of production and commercial valorisation that comes with it is incomparable.

The cost structure also changes profoundly. Labour systematically accounts for 50 to 70% of variable costs in strawberry production, and picking alone weighs 60 to 70% of that item. A switch to suspended gutters that improves hourly picking productivity by 15 to 20% has a direct impact on profitability — and that gain compounds over the entire service life of the structure.

The earliness gain as a value driver

Earliness is the primary economic argument for shelter investment, and is often underestimated in calculations. Technical reference data indicates that a standard market-garden tunnel advances harvest by 2 to 3 weeks compared to open-field production. A semi-forced low tunnel system can achieve a gain of 3 to 6 weeks. In a heated greenhouse with winter planting, first harvests are possible as early as March.

These extra weeks are positioned on a market where early-season prices are significantly higher than prices during peak production. Shelter investment should therefore be reasoned as much on the timing of the harvest as on the volume produced.

What the technical comparison cannot decide for you

This guide covers the main lines of choosing a strawberry shelter. It cannot answer the questions that depend on your specific situation — and it is precisely those questions that make the difference between a sound investment decision and a sizing mistake.

Should you open the vents on the 12th of April at 6am when the thermometer reads 8°C inside the tunnel, your Cléry plants are in full flower and a return of cold is forecast for the following night? Your north-south oriented multi-span on clay soil that retains moisture: at what RH threshold do you trigger the ridge ventilation to control Botrytis without disrupting flowering? You are planning to move to soilless on 3,000 m²: can your electrical installation and water network handle the automated fertirrigation that implies?

None of these questions has a universal answer. They depend on your variety, your pedoclimate, your phenological stage, your plot history and the current season. This is precisely what Fraisibot handles — in real time, with the precision of advice contextualised to your farm.

Access Fraisibot and secure your crop decisions now, with no appointment and no travel required.

Conclusion — Choosing your shelter means laying the foundations for fifteen years of management

The low tunnel, the multi-span and the heated greenhouse are not three versions of the same tool. They are three different production logics, with levels of intensification, crop systems and economic profiles that have little in common.

The low tunnel suits farms looking to secure two to three extra weeks of production with limited investment and maximum rotation flexibility. The multi-span with straight sides is the tool of intensive production — it opens access to soilless systems, yields of 40 to 70 t/ha and margins that justify a six-figure investment. The heated greenhouse is the answer to strategies of ultra-early positioning in premium markets.

None of these choices is made from a catalogue. It is built from the coherence between your commercial project, your surface area, your climatic zone, your target crop system and your investment capacity. And once the structure is in place, it is day-to-day management — ventilation, uncovering, shading, sanitary control — that determines whether it delivers on its promises over time.

Fraisibot answers your agronomic questions in real time, on every aspect of strawberry management under cover: from varietal arbitrage before planting through to managing a Botrytis episode in full flower. Discover our crop-specialist AI agronomic agents and make your technical decisions with the rigour of the best growers.