Strawberry plug plant growing guide
Econome à LégumesThe strawberry plug plant has become a standard in professional French strawberry growing. Its planting flexibility, vegetative reactivity and predictable time to first harvest make it a highly effective campaign management tool — provided every step of the growing itinerary is properly mastered. Because while the plug plant appears robust, it is precisely its prolonged dormancy period in cold storage that makes it demanding: from the moment of reception, every decision commits the season's yield trajectory.
From cold storage to harvest, the strawberry plug plant growing guide concentrates a series of critical decisions — variety and grade selection, thawing protocol, planting date, planting density, irrigation management during root establishment — whose effects accumulate on final yield. A poorly chosen grade can cost an entire season of commercial production. A botched thaw compromises rooting for the following four weeks. Insufficient irrigation in the fifteen days after planting reduces establishment and delays flowering.
This article documents the full itinerary, from plant selection to harvest, with the technical data needed for professional crop management: grades, planting densities by growing system, tensiometric thresholds, fertilisation programme by phenological stage, and key phytosanitary watchpoints.
What Fraisibot can resolve where this article cannot
This article gives you the technical benchmarks for the plug plant itinerary. But in real field conditions, some decisions resist any standardised framework:
- Your incoming batch of grade A- plug plants shows unusual crown heterogeneity — immediate planting or a few extra days in cold storage?
- You are combining two varieties with different maturity windows on the same plot: which planting density and planting window should you optimise to secure your marketing slot?
- Your tunnel heats up quickly in the morning towards the end of flowering — at what humidity threshold do you trigger preventive ventilation against Botrytis without compromising pollination?
What is a plug plant — definition and technical characteristics
A plug plant is a bare-root strawberry plant, harvested in autumn (typically in November) from runners produced by certified mother plants, then held in cold storage at a temperature maintained between -1.5°C and -1°C. This storage in a state of deep dormancy can last from a few weeks to several months, depending on campaign requirements and variety availability.
Cold storage serves two distinct functions. The first is logistical: it allows deliveries to be staggered and planting on demand, without being constrained by the natural biological window of vegetative regrowth. The second is agronomic: the metabolic arrest in cold storage concentrates reserves in the crown and roots. At planting, the plant restarts with accumulated energy which, depending on grade, translates into rapid production onset and high yield potential in the first year.
What fundamentally distinguishes the plug plant from the tray plant (plug or pot) is the absence of growing medium: the roots are bare, making them vulnerable to any desiccation or thermal shock upon removal from cold storage. This characteristic is what makes the first 48 hours after reception critical — and justifies a rigorous preparation protocol before planting.
Plug plant grades: reading a batch sheet and deciding
The grade of a plug plant is defined by the diameter of its crown (collar). There are five official classes, which directly determine expected first-year yield and speed of production onset.
Grading scale:
- A++: crown diameter greater than 18 mm
- A+: crown diameter greater than 15 mm
- A: crown diameter between 10 and 15 mm
- A-: crown diameter between 8 and 10 mm
- B: crown diameter between 6 and 8 mm
Impact on yield and speed to first harvest:
Grades A+ and A++ are the only ones capable of delivering significant commercial yield in year one: 250 to 400 g per plant from the planting season, with production onset around 60 days (8 to 10 weeks) after establishment. These are the reference grades for any strawberry production with a direct commercial purpose.
Grade A allows first-year production, but lower in volume and consistency than an A+ plant. Main production is often pushed to year two. Below grade A, commercial yields in year 1 are near zero: grade A- requires flower truss removal in the first season to build towards a second-year harvest, and grade B is strictly reserved for nursery transplanting.
Recommendation by growing system:
For production under tunnel or in elevated gutter systems targeting a specific marketing window, grades A+ and A++ are non-negotiable. For open-field bare soil with a two-year yield strategy, a homogeneous A batch may be acceptable, provided first-year expectations are adjusted accordingly.
Variety selection — maturity, market, disease behaviour
The variety choice determines the marketing window, resistance to pathogen pressures and fit with the intended sales channel. Strawberry plug plant varieties fall into four main groups according to maturity and fruiting type.
Early varieties (production onset April–May depending on region): Gariguette, Ciflorette, Clery, Honeoye, Kent. Valued on premium fresh markets and short supply chains for their aroma and earliness. Gariguette and Ciflorette are particularly sought after by farm shops and restaurants for their aromatic profile. Clery and Honeoye are better suited to intensive production with concentrated marketing.
Mid-season varieties: Elsanta, Darselect, Sonata, Polka, Korona, Malling Centenary. The varieties of the retail trade: consistent grading, good cold chain performance, high productivity. Elsanta remains a reference in Northern Europe for its ability to produce uniform volumes. Darselect is valued for its grade and adaptability to varied soils.
Late varieties: Malwina, Florence, Salsa, Arosa, Laetitia. They extend the season into July–August and capture marketing windows that open after spring volumes. Malwina stands out for its partial tolerance to powdery mildew, a useful trait under tunnel.
Everbearing varieties: Ostara, Portola, San Andreas, Monterey, Evie 2, Amandine. They produce continuously from May to October, with a possible mid-summer dip when temperatures exceed fruit set capacity. These varieties suit a regular delivery logic over a long season rather than a concentrated production peak.
Professional selection criteria beyond maturity:
Maturity is only the first filter. The following criteria are decisive for a profitable variety decision:
Commercial destination radically shapes the choice. For the fresh market via farm shops or restaurants, aromatic profile and visual appeal take precedence over raw grade. For retail, grade consistency, cold chain performance and shelf life matter more than flavour. For processing (jam, freezing), the criteria are reversed: firmness, sugar content, tolerance to mechanical sorting.
The pedo-climatic and phytosanitary context of the plot is a frequently overlooked filter. On soils that have received sensitive previous crops (solanaceous crops, strawberries themselves), the risk of Verticillium dahliae makes it essential to favour partially tolerant varieties — San Andreas and Ventana show documented partial resistance to this pathogen. In regions with high powdery mildew pressure (tunnels in wet areas), varieties such as Malwina or Rumba reduce fungicide pressure. In areas with high Botrytis pressure during flowering, a variety with more open flower architecture (petals drop quickly) mechanically reduces residual inoculum.
Season extension is a major economic lever in professional production. Combining an early variety (Clery or Gariguette for the first weeks), a main-season variety (Darselect or Elsanta for peak volume) and a late variety (Malwina or Florence for the back end of season) allows workload at harvest to be smoothed, cash flow spread and commercial presence maintained over several months.
Note on licensed varieties: The majority of recent commercial varieties (Clery, Darselect, Malling Centenary, Sonata, Malwina, Portola, San Andreas...) are protected by plant breeders' rights. Any reproduction, even for the farm's own use, constitutes a breach of European regulations. Sourcing certified plants from a licensed nursery is the only legal route for protected varieties.
Reception and plant preparation — the 48 hours that determine establishment
The quality of vegetative establishment is largely determined in the hours following lot reception. Plug plants removed from dormancy at -1.5°C are in a physiologically fragile state: bare roots are sensitive to desiccation and thermal shock, and metabolic reactivation must be gradual to avoid burning root tissue.
Thawing protocol
On reception, plants must be stored in shade, sheltered from wind and direct sunlight. Thawing must be slow and progressive, until the core temperature of the bundle reaches 4°C. Direct sun exposure or high ambient temperature creates a thermal gradient between the outside and core of the batch that can scorch outer tissue before the centre has thawed.
Rehydration
Once thawed, plants must be submerged roots-down in clean water for 15 to 20 minutes. This soaking rehydrates root tissue and definitively breaks dormancy. Root dipping (clay + water + optionally a root biostimulant) may be carried out at this stage to optimise establishment, particularly on drying soils or in difficult planting conditions.
Root and foliage preparation
Overly long roots are trimmed to 10 cm from the crown. This trimming is not an amputation — it stimulates lateral root hair production and improves soil-to-root contact at planting. If large leaves are present (plants harvested late or from short storage), they may be partially removed. Heart leaves (young leaves developing at the centre of the rosette) must be preserved — they sustain photosynthesis at restart.
Time to planting
Once thawed and rehydrated, plants break dormancy irreversibly and rapidly. There is no defined post-thaw holding period: the operational rule is to plant on demand, without allowing roots to dry out or plants to be exposed to open air. Every hour spent out of the ground or out of moist storage after thawing is an hour of root stress that penalises establishment.
Planting dates and densities — the variables that structure the campaign
The plug plant planting window generally runs from March to late May, with variation according to region, growing system and production objective.
The advantage of early planting
March plantings offer a structurally important agronomic advantage: cool temperatures slow aerial growth in favour of root development. Deep, dense rooting early in the season translates into better summer drought resistance and more consistent production. Late plantings (May) expose plants to a warmer spring that accelerates vegetative growth at the expense of root consolidation.
In regions with late winters (altitude, north-facing plots, cold soils), planting may be delayed to April without significant yield penalty. Logistical constraints around variety supply, availability of planting equipment and labour scheduling are real factors that shift the theoretical window.
Planting densities by growing system
Optimal densities vary significantly by system:
- Open field, single row: in-row spacing of 25 to 30 cm, between-row spacing of 80 to 100 cm, equating to 33,000 to 50,000 plants/ha (3.3 to 5 plants/m²). This system suits extensive production and vigorous varieties.
- Open field or tunnel, double row on raised bed: in-row spacing of 20 to 25 cm in a staggered arrangement, bed centre-to-centre distance of 80 to 120 cm, equating to 55,000 to 80,000 plants/ha (5.5 to 8 plants/m²). The double row maximises ground cover and improves light distribution between plants.
- Soilless, elevated gutter system: on-line spacing of 20 to 22 cm, gutter-to-gutter spacing of 80 to 110 cm, equating to 45,000 to 110,000 plants/ha (4.5 to 11 plants/m²). This system allows the highest densities and complete control of growing medium, irrigation and nutrition, but requires significant infrastructure investment and a high level of management skill.
Row orientation and soil preparation
Row orientation (north–south for balanced light exposure on both sides) and seedbed preparation (subsoiling, ridging or raised bed according to drainage) determine rooting quality after planting. On soils at risk from Phytophthora or Verticillium, planting on a raised bed (15 to 20 cm) reduces contact with infested soil zones in wet conditions.
Post-planting management: irrigation, fertilisation, mulching
Irrigation — from planting to flowering
Critical root establishment phase (Day 0 to Day +15):
At planting, an immediate application of 200 to 300 mL of water per plant is essential to ensure soil-to-root contact. Over the following fifteen days, irrigation must maintain constant moisture around the developing root system: short, frequent applications of 2 to 6 mm/day (0.3 to 0.5 L/plant) prevent surface drying without waterlogging.
The risk during the establishment phase is twofold: soil that is too dry compromises soil-to-root contact and delays establishment; excess moisture, particularly in mild weather, promotes Botrytis at the crown and Phytophthora root rot. Managing irrigation in the first two weeks is therefore a daily trade-off between securing establishment and controlling fungal risk.
Tensiometric management:
From vegetative regrowth through the rest of the season, irrigation managed by tensiometric probes allows precise adjustment to actual crop needs. Target values are as follows:
- Vegetative stage: maintain tension between 10 and 20 kPa
- Flowering and fruit swelling: narrow to 10 to 15 kPa, with a typical trigger at 15 kPa, stopping at 8–10 kPa
Daily water requirements by phenological stage:
- Root establishment / regrowth: 0.3 to 0.5 L/plant (2 to 6 mm/day)
- Vegetative growth: 0.2 to 0.4 L/plant (2 to 5 mm/day)
- Flowering: 0.3 to 0.5 L/plant (3 to 6 mm/day) — avoid wetting flowers to prevent pollen washout and Botrytis on petals
- Fruit swelling and harvest: 0.4 to 0.7 L/plant (4 to 8 mm/day) — peak demand, representing nearly 50% of seasonal water volume
Fertilisation — stage-by-stage logic
Overall crop requirements:
For professional-level yield, strawberries require over the full season between 60 and 120 kg/ha of nitrogen (N), 40 to 80 kg/ha of phosphorus (P₂O₅) and 100 to 180 kg/ha of potassium (K₂O).
Programme by stage:
- Pre-planting / establishment: 100% of phosphorus and 50 to 60% of potassium must be incorporated as base dressing before planting. Nitrogen is applied at 30 to 40% before establishment. At planting, a localised micro-dose of diammonium phosphate (starter) supports early root development.
- Vegetative regrowth: 20 to 30 units of additional nitrogen and potassium via fertigation to stimulate leaf development.
- Flower initiation: nitrogen must be significantly reduced at this stage to avoid overly vigorous vegetative growth that would delay flowering and expose inflorescences to Botrytis. Phosphorus and potassium take over.
- Fruit swelling and harvest: potassium (K) becomes the priority element — it governs sugar content, fruit grade and firmness at harvest.
Specific role of calcium:
Calcium (total requirement of 30 to 120 kg CaO/ha) is a frequently underestimated element in plug plant strawberry management. It is essential for cell wall consolidation and fruit firmness. Calcium deficiency manifests as soft fruit, apical necrosis (brown fruit tip, or "tip burn") and leaf scorch. Applications must be split: calcium nitrate via fertigation or repeated foliar application at fruit swelling and ripening, when demand is highest.
Mulching
Mulching performs four simultaneous functions in strawberry growing: maintaining soil moisture, suppressing weeds, regulating soil temperature at the start of the season, and reducing basal Botrytis contamination from splash (soil spores projected onto fruit during irrigation or rainfall).
Black or black/white co-extruded plastic film is the standard for intensive production. Black film absorbs solar radiation and warms the soil by 2 to 4°C early in the season — a significant advantage for March plantings. Black/white bi-face film (white side facing up) is preferred in regions with high solar radiation or under tunnel: it reflects light towards developing fruit, limits excessive soil warming in summer and reduces the risk of root scorch. In both cases, the film virtually eliminates weeds, maintains moisture by reducing surface evaporation and isolates fruit from direct soil contact — mechanically reducing basal Botrytis contamination.
Organic mulch (cereal straw) remains a viable alternative in organic production or low-input systems. It improves long-term soil structure and promotes biological activity, but requires annual replacement, does not warm the soil as effectively as plastic and allows sufficient light penetration for weed germination between rows. Its effectiveness against soil splash is comparable to plastic provided sufficient depth (8 to 10 cm) is applied.
Harvest and crop cycle — planning the end of season
Harvest window and maturity indicators
The harvest window for plug plants runs from mid-May to mid-October depending on region, variety and growing system. For early varieties planted in March under tunnel, first harvests can begin from late April in the most southerly areas. For late open-field varieties, harvest can extend through July–August.
Maturity indicators at harvest are colour (uniform red colouration across the entire fruit, with no residual white areas near the calyx), firmness (fruit yields slightly to pressure without being soft) and aroma (variety-specific olfactory development). For farm shops and direct sales, harvest at full maturity. For long supply chains (retail, wholesalers), harvest slightly ahead of full maturity to preserve cold chain performance.
Harvest organisation during peak season
In full season, picking frequency is decisive for lot quality and commercial value. An over-ripe fruit left on the plant is a potential Botrytis reservoir: released spores contaminate adjacent fruit and can compromise the entire next picking run. The recommended frequency is one pass every two days during sustained production, with systematic removal of damaged or downgraded fruit at every pass.
Morning harvest (before temperatures rise under tunnel) is preferable for maintaining fruit firmness and extending post-harvest shelf life. A fruit picked at 28°C in mid-afternoon under tunnel keeps approximately half as long as one picked at 16°C in the morning.
Crop cycle length and replanting decision
Plug plant crops generally run on a one- to two-year cycle depending on the farm's strategy. In annual cropping (intensive tunnel or soilless model), plants are removed at the end of the season and replaced with a new batch the following year. This model maximises per-plant productivity and maintains the sanitary status of the substrate or soil, at the cost of annual plant procurement.
In a biennial cycle (more extensive open-field model), plants are retained for a second year. Second-year production is generally earlier (crowns are already developed) but the phytosanitary status of the plot must be assessed: Verticillium and Phytophthora accumulate in the soil over successive cycles, and a plot that has experienced significant pressure in year one exposes plants to increased risk in year two. The decision to retain or replant must incorporate the end-of-first-campaign phytosanitary assessment.
Phytosanitary protection — key watchpoints specific to plug plants
Plug plants have a specific sensitivity profile to certain pests and diseases in the weeks following planting, due to the absence of a protective growing medium and the progressive nature of root establishment.
Botrytis cinerea — the absolute priority
Botrytis cinerea (grey mould) is the most feared fungal disease in strawberry growing, with particularly high pressure in the first weeks after planting and during flowering.
The epidemic trigger conditions are precise: temperatures between 15°C and 25°C combined with relative humidity above 75%. Under a closed tunnel in spring, these conditions are frequently met in late morning over several hours.
The phenological stages carrying priority risk are:
- BBCH 51–59 (inflorescence emergence): first strict monitoring window, as flower buds are primary infection sites
- BBCH 69–71 (fruit set): falling residual petals provide major inoculum substrate
- Fruit swelling and ripening: critical downgrading window where the epidemic can accelerate exponentially if over-ripe or damaged fruit remains on the plant
Preventive management relies on shelter ventilation (open vents when hygrometer exceeds 80%), systematic removal of fruit and plant debris at every picking pass, and maintaining sufficient plant spacing to prevent stagnant humid air within the canopy.
Powdery mildew (Podosphaera aphanis)
Powdery mildew presents as a white powdery coating on the underside of leaves, flower buds and sometimes fruit. It develops preferentially under tunnel in confined, mild conditions (moderate temperatures, low absolute humidity but high relative humidity). Prevention relies on shelter ventilation and control of nitrogen inputs — overly vigorous foliage, driven by excess nitrogen, is consistently more susceptible to powdery mildew.
Soil-borne diseases — Verticillium and Phytophthora
Two soil-borne pathogens warrant particular attention in plug plant itinerary management, as they become permanently established in the soil and their presence conditions rotation and variety selection decisions for several years.
Verticillium wilt (Verticillium dahliae) causes progressive wilting without visible rot: leaves yellow and necrose from the base upward, vascular tissue browns at the cut. The fungus is a vascular parasite colonising the xylem with no effective curative treatment available. Prevention is absolute: minimum 8-year rotation without strawberries on contaminated ground, exclusion of sensitive previous crops (solanaceous crops in particular), sourcing of certified disease-free plants, and selection of partially tolerant varieties where an at-risk history exists.
Phytophthora cactorum attacks the crown and roots, causing rapid wilting in warm conditions. Roots rot and the crown base browns distinctly. This pathogen develops under conditions of excess moisture at the root profile — which is why raised bed planting and adequate soil drainage are preventive measures directly integrated into system choice. In soilless growing, Phytophthora risk is virtually eliminated by control of the growing medium and drainage.
Spider mites (Tetranychus urticae) proliferate in hot, dry conditions, particularly under tunnel in summer. They present as yellow mottling on the upper leaf surface and a fine webbing on the underside. Integrated management favours introduction of predatory mites (Phytoseiulus persimilis, Amblyseius californicus) and maintenance of adequate humidity.
Aphids colonise the underside of young leaves and are virus vectors. Particularly problematic in nurseries and early in the season, they require weekly monitoring and early intervention (beneficial insects, insecticidal soap) to prevent spread.
Why a standardised itinerary cannot resolve your plot-level decisions
The plug plant itinerary is documented, the data exists, the technical thresholds are known. Yet underperformance in strawberry production remains common — and it rarely stems from unfamiliarity with general principles. It stems from the impossibility of cross-referencing the real variables of each individual farm in a standardised guide.
Your A+ Darselect planted in week 13 on a raised bed on loamy soil in a bi-span tunnel in Brittany is not managed the same way as a batch of A++ Clery planted in week 10 in an elevated gutter system in Roussillon. The tensiometric thresholds remain the same, but irrigation trigger frequency, run duration, fertilisation programme and phytosanitary strategy are variables that only a combination of pedo-climate × variety × system × growth stage can determine correctly.
Some real decisions this guide cannot resolve for you: your late-arriving batch shows slightly desiccated roots — is an extra hour of soaking sufficient, or should you reconsider immediate planting? Your tunnel reaches 28°C by 10am at early flowering — at what humidity threshold do you cut ventilation to avoid compromising pollination by the bumblebees already in place? In week 18, your plants enter fruit swelling and your tensiometer reads 18 kPa at 20 cm depth — do you trigger irrigation now or wait for confirmation at 25 cm?
These decisions commit your yield, the phytosanitary quality of your lot and sometimes an entire week of production. They require a response tailored to your situation, not a general rule.
From reception to harvest: mastering the itinerary, adapting the advice
The strawberry plug plant growing guide is a sequence of interdependent decisions whose mastery directly determines yield and campaign quality. Grade matched to commercial objective, rigorous thawing protocol, planting within the optimal window, density adjusted to the system, precise tensiometric irrigation management, stage-by-stage fertilisation and reasoned phytosanitary monitoring: each step carries its own level of risk, and every deviation has a measurable cost in yield or quality.
The technical data exists. What differentiates growers is the ability to apply it in real time to the reality of their plot.
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