Tray plant strawberry growing guide
Econome à LégumesProfessional strawberry growing has been profoundly reshaped around a central trade-off: which planting material for which commercial window? The tray plant has established itself as the technical answer for early markets — the one that captures the value of the first French strawberries in March and April before Spanish imports flood the distribution networks. In 2024-2025, France produces around 55,000 tonnes of strawberries per year but remains structurally in deficit against Iberian volumes. The only defensible position for the French producer is earliness and flavour quality — two levers that the tray plant addresses directly.
The promise is clear: a harvest 3 to 4 weeks earlier than a cold-stored plant, with yields of 400 to 600 g per plant over a 90-day cycle. But this promise is only fulfilled under one condition: a precisely managed growing programme, from plant material selection through to EC management of the nutrient solution at fruiting.
For a grower managing 3,000 m² of tunnel or one hectare of substrate gutter systems, tray plants represent a significant financial commitment — between €0.75 and €0.80 per unit compared to €0.20–0.45 for a cold-stored plant. This higher planting cost is only recouped if the commercial window is effectively captured. A 15-day gap on the first harvest date often means the difference between selling at €4–5/kg and joining the market at import price. A poorly managed tray plant batch — water stress at establishment, night temperature too low during flowering, EC drainage drifting above 2.0 mS/cm — can turn a premium investment into a loss-making season.
This article explores the key technical variables of the tray plant programme: plant material selection, planting calendar by zone and system, planting technique, climate management under cover, fertirrigation by phenological stage, and integrated biological pest management on short cycles.
Fraisibot answers your questions on tray plant management
Before going further, here are the types of questions strawberry growers ask when planning their season with tray plants:
- Standard tray plant or mini-tray: which to choose based on my system — mulched soil under tunnel or substrate gutter — and my market — direct early sales or retail chains?
- Planting end of December or mid-January: what is the real impact on my first harvest date in a northern zone, given that my tunnels have no active heating?
- Intake inspection: my batch shows reddish rhizomes on 3% of checked root balls — do I plant or reject the lot?
- Fertirrigation at establishment: what EC target for the first 15 days to favour rooting without salt stress on a plant whose floral induction is already complete?
These decisions play out within hours of intake or planting. Fraisibot, Agronomia's specialised strawberry agronomic AI advisor, provides real-time answers to these trade-offs taking into account your growing system, your climatic zone and your variety.
Tray plant, mini-tray, waiting bed: what the terminology actually means
The professional strawberry plant market covers very different realities under names that are sometimes used interchangeably. Getting the terminology right is a prerequisite for any planting decision.
The tray plant is a premium plant grown in cell trays, with a root ball volume of 5 to 10 cm³. Its structural advantage lies in floral induction, completed entirely at the nursery before delivery. The plant arrives ready to produce: establishment is near-instantaneous, and the first harvest flush is predictable at around 90 days after planting, with a yield of 400 to 600 g per plant depending on variety and management. This level of predictability — rare in agriculture — is what justifies the higher planting cost.
Understanding the floral induction mechanism is essential, as it drives the entire logic of the programme. At the nursery, the strawberry plant is exposed to short days and cool temperatures to trigger the initiation of floral primordia. By the time the plant is delivered, those primordia are already formed. The plant begins its reproductive cycle almost immediately after planting, without waiting for the next induction-suitable period. This is precisely why establishment root management is critical: the plant must simultaneously anchor itself in its new medium and sustain a heavy flowering load.
The mini-tray is a variant grown in smaller pots of approximately 6 cm in diameter, with a lower root volume. Its cycle is shorter — around 60 days after planting — with yield performance equivalent to the standard tray. It is particularly suited to short cycles in substrate systems, where turnover speed takes priority over volume per plant. Its lower unit cost compared to the standard tray makes it a relevant option for intensive gutter systems running at high planting density.
The waiting bed (WB) follows a different logic: it is a cold-stored plant re-established in open ground at the nursery, lifted in December and returned to cold storage. Its calibre is not measured by root ball volume but by crown diameter: Light (15–18 mm), Medium (18–22 mm), Heavy (over 22 mm). Its harvest lead time is slightly longer — around 105 days — with a yield of 300 to 500 g per plant. Its intermediate cost (€0.50–0.60) makes it a compromise between performance and investment, relevant for growers who want to spread their risk across several types of planting material.
The following table summarises the key decision parameters:
| Plant type | Structure | Floral induction | Harvest lead time | Yield/plant | Unit cost |
|---|---|---|---|---|---|
| Tray plant | Cell tray, 5–10 cm³ | Done at nursery | ~90 days | 400–600 g | €0.75–0.80 |
| Mini-tray | Pot ~6 cm Ø | Done at nursery | ~60 days | Equivalent to tray | < tray |
| Waiting bed | Crown Ø 15–22+ mm | Partial | ~105 days | 300–500 g | €0.50–0.60 |
| Cold-stored plant A/A+ | Bare root | Not done | ~120 days | 250–400 g | €0.20–0.45 |
Plant health certification governs every purchase decision. Always require a CAC-certified plant (Conformitas Agraria Communitatis), guaranteeing freedom from the four major viruses — SMoV, SVBV, SMYEV, SCV — as well as from Aphelenchoides fragariae nematodes and tarsonemid mites. An uncertified plant at a lower price can compromise the entire plot. On material costing €0.75–0.80 per unit, the saving made on an uncertified batch never covers the cost of replanting.
Planting calendar: reading the signals from your zone and system
The planting date for a tray plant is not a free choice — it is the result of a back-calculation from the target commercial window, adjusted for growing system and climatic zone. A grower who misses their tray plant window by 15 days plants part of their investment directly into competition with imports.
Cold tunnel or greenhouse — southern zones: planting in August-September, expected harvest from December to May. This slot corresponds to premium early production, ahead of the ramp-up in Iberian imports. Extreme earliness is the only economic argument that holds durably against Spanish volumes. Mediterranean zones benefit from mild winters enabling rapid vegetative restart — but some varieties require a minimum chilling sum that these zones do not always provide. Variety choice is critical here.
Forced tunnel — Atlantic or northern plains: planting of cold-stored tray plants in September-October, harvest in April-June. The window is less premium but structure costs are often lower. Spring frost risk must be anticipated, particularly on exposed or hollow sites. In northern or continental zones, production is concentrated in a narrow window, and in-soil tunnel growing often retains an advantage over substrate systems in terms of natural thermal buffering and lower capital cost.
Winter planting under heated cover (December-January): this is the most technically demanding programme, targeting a first harvest in March-April — the highest price slot for French strawberries. It requires a structure with active thermal regulation capacity and rigorous climate management.
For substrate gutter systems, planting density rises to 7.5–11 plants/m², versus 5–6 plants/m² in mulched soil on single or double rows. The density gain is a gross yield lever, but it amplifies demands on irrigation management, ventilation and pest control — a dense gutter system is an ideal environment for a spider mite population explosion or an undetected Botrytis focus.
| Zone | System | Plant type | Planting period | Expected harvest |
|---|---|---|---|---|
| Southern Mediterranean | Cold greenhouse / tunnel | Standard tray plant | August–September | December–May |
| Atlantic plain / north | Forced tunnel | Cold-stored tray plant | September–October | April–June |
| All zones | Heated cover | Tray plant or mini-tray | December–January | March–April |
| Substrate gutters | Tunnel or greenhouse | Mini-tray | Variable | 60-day cycle |
On variety selection for winter forcing, professional references converge on varieties with low chilling requirements and fast response under cover. Gariguette and Ciflorette remain reliable choices for the premium early market — flavour, earliness, commercial recognition. Clery stands out for productivity and firmness for retail export. For mid-December to mid-January plantings targeting very early harvest, Dély, Flair and Twist are options proven by professional winter forcing specialists. Variety choice commits the entire season and the entire value chain — and must be finalised before ordering plants, not after intake.
Planting: the adjustments that determine establishment
Planting quality determines root establishment, which determines the plant's ability to sustain the flowering load imposed by nursery-completed induction. A poorly planted tray plant is a contradiction in terms: you purchase the earliness of floral induction and undermine it at the very first step.
Intake inspection: before any planting, visually inspect 1% of the root balls in the batch. The three pathogens to identify are:
- Phytophthora cactorum: crown blackening, generalised wilting of the plant. If the root system shows a black "rat tail" appearance, suspect Phytophthora fragariae, whose impact on the plot is even more severe.
- Colletotrichum acutatum (anthracnose): black spots on leaves (0.5–1.5 mm), dark oval lesions on petioles. A cross-section of the rhizome showing a reddish tinge inside is a strong indicator — do not plant.
- Verticillium dahliae: asymmetric wilting — often 50% of the foliage affected — stunted, weak-looking plant. Darkening of the vascular tissue visible on cross-section.
The professional tolerance for these three pathogens is zero. Any batch showing red rhizomes, blackened crowns or rot at inspection must have the affected plants immediately destroyed. Planting a suspect batch to "wait and see" is an economically unacceptable risk on material at €0.75–0.80 per unit, and even more so on plots that will be difficult to clean up before the following season.
Soil preparation and ridges: deep decompaction to 35–40 cm, pre-planting organic amendment (20 to 40 t/ha of mature compost depending on initial organic matter level). Ridges 20 to 30 cm high, promoting drainage, soil warming and harvest ergonomics. Black polyethylene film under normal conditions, black/white bicolour film in warm seasons to limit root zone overheating.
Planting depth: the crown must be at soil level, never buried. The crown must not be forced into a hole that is too small — prepare the space to receive the root ball without constraining or bending the roots. A buried crown favours crown rots; a crown set too high exposes roots to desiccation.
Irrigation at establishment: the first 15 days are critical. The goal is to encourage root exploration without waterlogging — a saturated soil at establishment favours Phytophthora and slows anchoring. Frequent short irrigations rather than long infrequent ones, to keep the root ball moist without saturating the surrounding substrate.
Fertirrigation by phenological stage: precision management
This is the section that generic guides skim over — yet it is what separates a controlled season from a reactive one. In a tray plant substrate or tunnel system, the root system is confined and responds almost instantly to inputs. There is no soil buffer to correct a drift. Electrical conductivity (EC) and pH of the drainage solution must be monitored continuously.
Permanent monitoring parameters: drainage EC maintained between 1.4 and 2.2 mS/cm depending on stage, target pH 5.5 to 6.5. In direct fertirrigation, target an EC of 1.2 to 1.5 mS/cm in the vegetative phase, 1.5 to 1.8 mS/cm in the production phase. Never exceed the critical threshold of 2.0 mS/cm — beyond this, the plant experiences salt stress leading to reduced yield and fruit firmness, difficult to recover from on such a short cycle.
Establishment phase (D0–D15)
The objective is plant establishment, not production. A light localised application of diammonium phosphate in microdose (starter effect) promotes initial root development. Balanced N-P-K ratios such as 10-10-10 or 14-14-14 are suited to this phase — balanced inputs that support the plant without forcing it. Nitrogen must remain moderate to avoid stimulating excessive vegetative growth at the expense of rooting.
Vegetative growth and floral initiation
The plant builds its canopy and prepares for flowering. A nutrient solution supplying 20 to 30 units of nitrogen and 20 to 30 units of potassium is preferred. A 4-6-12 (N-P-K) fertiliser may be used pre-flowering. The objective is to build a leaf canopy sufficient to sustain the coming fruit load, without creating lush vegetation that would favour Botrytis and powdery mildew.
Flowering
Inputs are moderate and balanced. This is the stage at which micronutrients play a critical role. Boron (B), applied as a foliar spray, supports fruit set and pollen quality. Calcium, also applied foliarly, prevents flower abortion and prepares the firmness of future fruits. A boron deficiency at flowering results in irregular fruit set and deformed fruits — a problem that is difficult to correct on a cycle of only 60 to 90 days.
Fruit swelling and production
The balance shifts towards potassium. It is potassium that drives sugar content (Brix), fruit size and partly firmness. Recommended forms are potassium sulphate, calcium nitrate and monopotassium phosphate (MKP), with high-potash fertilisers (such as 0-0-30). Repeated foliar calcium applications — calcium nitrate as priority — prevent fruit softening and are critical for export shelf life.
Adjustment by market outlet: the potassium/calcium balance must be adjusted to match the commercial objective. For direct sales and fresh markets, push Brix — dominant potassium inputs. For retail chains and long-distance export, prioritise firmness — dominant calcium, measured potassium. An excess of potassium aimed at high Brix produces fruit that does not hold in a punnet after 48 hours of transport.
Managing the crop under cover: climate, IPM and pest control
Thermal management
Temperature is the primary control variable in the tray plant programme under cover. Optimal daytime temperature is 18 to 22°C. At night, the optimum is 10 to 13°C. Alert thresholds are precise and non-negotiable:
- Vegetative arrest below 5°C
- Flower frost (black heart) from -1°C
- Irreversible damage to newly set fruit from -0.5°C — flower abortion and deformed fruits
- Night temperature exceeding 20°C: drastic reduction in fruit set
Marked day/night temperature swings must be avoided in winter — ventilate on bright days even in cold weather, to prevent scorching and maintain humidity around 60%. At the 2–3 mm flower bud stage, daytime temperatures between 8 and 12°C for just one day cause fruit deformations visible 30 days later. This is a short vulnerability window with lasting consequences on the corresponding harvest flush.
Pollination under closed cover: install 1 bumblebee hive per 500–1,000 m², positioned at crop height, entrance facing the crop, sheltered from direct sunlight. Do not introduce the hive before 5 open flowers per square metre are present — the risk of over-buzzing (pollen collected without effective pollination, causing fruit deformation) is real if introduced too early. Avoid all insecticide or acaricide treatments during full flowering.
Botrytis cinerea management
Botrytis is the primary fungal risk on tray plants under tunnel — it can destroy an entire flowering flush within days under favourable conditions. Triggering conditions are precise: temperature between 15 and 25°C combined with relative humidity above 75%. These conditions are easily reached in a closed tunnel during the transitional season.
The strategy is built on climate-based prophylaxis first — keeping humidity below 75% through active ventilation even in winter, avoiding draughts that create cold spots. Rapid removal of plant debris (fallen petals, mummified fruits) is essential — they act as inoculum reservoirs. In biological control, Bacillus amyloliquefaciens (Serenade, Amylo-X) is applied preventively before flowering stages. Conventional fungicide interventions (SDHIs + benzimidazoles in alternation) are timed at 2 to 3 applications per flowering period, observing the pre-flowering interval to avoid affecting pollinators.
Powdery mildew management (Podosphaera aphanis)
Powdery mildew is frequently underestimated by growers starting out with winter heated tunnel tray plants — this is a mistake. This pathogen thrives precisely in the conditions created by heated cover: temperatures between 10 and 25°C, confined air, high humidity without free water. Day/night temperature swings generate morning dew inside tunnels — ideal conditions for its development.
Unlike Botrytis, powdery mildew does not need free water — rain actually washes away its spores. The confinement of a winter or early spring tunnel is its ideal environment. Prophylactic rigour means strict ventilation to avoid stagnant air, micronised sulphur applied preventively (evening or early morning to avoid scorching), potassium bicarbonate, and Bacillus subtilis. Never wait for the first visual symptoms to intervene — by that point, the pressure is already established.
Spider mites and thrips: IPM on the short cycle
On a short tray plant cycle (60 to 90 days), pest populations can explode within days in a confined, warm environment. IPM is built on anticipation — preventive releases must precede pest pressure, not follow it.
Two-spotted spider mite (Tetranychus urticae): introduce Neoseiulus californicus or Phytoseiulus persimilis preventively at the first temperature rises above 12°C, or at the very first isolated mite observations. The curative intervention threshold is 5 individuals per 10 leaves — beyond this, pressure is difficult to contain with beneficials alone, and acaricides (abamectin, spiromésifen) become necessary in rotation of active substances.
Western flower thrips (Frankliniella occidentalis): monitor using blue sticky traps from planting onwards. Position Neoseiulus cucumeris or Amblyseius swirskii, and the predatory bug Orius spp., preventively before full flowering — ideally from the appearance of the first flowers. The curative threshold is 2 thrips per flower. Beyond this, biopesticides (spinosad, compatible with organic production) or acetamiprid (outside flowering only) must be deployed. Early intervention is critical — thrips damage achenes and produce corky, commercially downgraded fruits.
Yields observed under professional conditions reflect the complexity of the variables at play: 20 to 36 t/ha in mulched soil under cold tunnel, 35 to 60 t/ha in substrate gutter systems, up to 40 to 70 t/ha in optimised short cycles. These wide ranges are not imprecisions — they reflect the actual spread of results observed depending on how each operation is managed.
To manage your tray plant fertirrigation and IPM programme in real time — interpreting deficiency signs, adjusting EC by stage, diagnosing a fungal or pest focus — our crop-specialist agronomic AI advisors are available 24/7, with no appointment and no travel required.
Why the same programme delivers opposite results from one farm to the next
This is the question strawberry growers regularly ask after a disappointing tray plant season: the programme was correct on paper. The answer lies in the combination of variables that a generic guide cannot resolve for a specific situation.
The climatic zone reshapes every parameter. In Mediterranean zones, mild winters enable a rapid vegetative restart — but they also reduce the chilling sum available for some varieties and create early pest pressure. In northern or continental zones, spring frost risk is higher, the production window narrower, and in-soil tunnel growing often retains an advantage over substrate systems in terms of natural thermal buffering. The same Gariguette tray plant planted in late December will deliver radically different results in Perpignan and in Brittany — even in identical cover systems.
Variety interacts with system and zone. Gariguette under heated cover in December does not behave like Clery in the same system, nor does it target the same commercial outlet. Flair will be more tolerant of difficult winter conditions than an early variety with low cold hardiness. Twist responds differently from Dély to temperature swings under tunnel. Variety choice commits the entire season and the entire value chain — and must be finalised before ordering plants.
Plant batch quality varies between nurseries and between seasons. The actual level of floral induction achieved at the nursery directly affects the size of the first flush and the effective harvest lead time. Two batches of tray plants of the same variety, bought at the same price, can deliver very different results depending on the climatic history of the nursery at induction time. This variable is invisible at intake — it only reveals itself at flowering.
The combination of fertirrigation × under-cover climate × IPM is a system of interdependent variables. Water stress at establishment weakens the root system and compromises the plant's ability to sustain flowering. Poorly managed humidity at flowering favours Botrytis cinerea, which sterilises stamens. EC drifting above 2.0 mS/cm at fruiting reduces fruit firmness. An undetected thrips focus before flowering produces damaged achenes and corky, downgraded fruits. Each of these errors is independent — and their combination is potentially catastrophic on a 60 to 90-day cycle that allows no time for recovery.
These interactions cannot be read in a generic technical guide. They are diagnosed from the actual parameters of your operation — system, zone, variety, phenological stage, plot history — and require a response tailored to your situation, not a standardised prescription. This is precisely what our crop-specialist agronomic AI advisors are designed to address.
Conclusion
The tray plant programme is a genuine competitiveness lever for the professional strawberry grower targeting early market slots or seeking to extend their production window. The potential is documented: 60 to 90-day harvest lead times, 400 to 600 g per plant, up to 40 to 70 t/ha in optimised substrate systems. But this potential is not automatic — it is conditional on a chain of interconnected decisions, from plant type selection through to EC management of the nutrient solution at fruiting, climate control under cover and anticipation of pest pressure on the short cycle.
The technical guide sets the parameters. It cannot make the trade-offs for you, because your zone, your system, your variety, your batch quality and your market outlet create a combination that is specific to your operation — and that evolves throughout the season.
Fraisibot, Agronomia's specialised strawberry agronomic AI advisor, is available 24/7 to answer your real-time management questions — whether arbitrating between two plant types before ordering, adjusting your fertirrigation programme by growth stage, diagnosing abnormal behaviour at establishment, or timing your beneficial insect releases ahead of flowering.
Discover the full range of crop-specialist agronomic AI advisors on Agronomia.