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Plug plant strawberry production: from delivery to winter dormancy

Econome à Légumes

A strawberry crop starts well before the first harvest. It starts the moment the grower decides which type of plant to use, and when. With plug plants and pot plants, that decision commits the entire season: a plant delivered in active growth in August cannot afford an approximate planting, or a week's delay. Unlike cold-stored runners — stockable, flexible, plannable — the plug plant arrives alive and growing, demanding near-immediate planting in a window measured in days, not weeks.

For a professional strawberry grower, mastering this production pathway directly determines first-year yield. With establishment costs that can exceed €12,500/ha in plants alone, the margin for error is narrow at every step — from plant delivery to laying the winter fleece in October.

This article details the key technical decisions of the plug plant pathway, from delivery to the threshold of winter. No universal protocol applies to all growing systems — the variables are too numerous: variety, soil and climate, production system, commercial objective. What can be documented is the real complexity of each stage, and what it means for decision-making.

Three questions a strawberry grower actually faces in August and September:

  • My delivery shows root heterogeneity — some plugs have a well-developed root ball, others don't. Do I accept the batch or reject it?
  • My plants are showing the first flower trusses 10 days after planting. Should I remove them all, and until what date?
  • The soil is still warm and slightly dry after the previous crop. Do I plant now, or wait for better conditions and risk losing 5 days in the useful planting window?

These are decisions made in the field, in real time, with whatever information is available at that moment. Fraisibot, Agronomia's AI agronomist specialising in strawberries, guides you stage by stage through crop management from plant delivery onwards. Discover Fraisibot →

The plug plant: what it is, what it demands on delivery


Definition and propagation process

The plug plant — often called a pot plant — is a fresh strawberry plant propagated from a runner taken in June or early July from certified mother plants. The runner is rooted in an individual container in a propagation greenhouse over 21 to 28 days. Once the plug is sufficiently colonised by roots, the plant is ready for delivery: typically from late July onwards, with deliveries staggered through to early September depending on the nursery and order schedule.

This production method fundamentally distinguishes the plug plant from the cold-stored runner, which is lifted after winter dormancy, held at low temperature in cold storage, and delivered without active foliage. The plug plant arrives in full vegetative growth: developed leaves, roots actively colonising the plug, energy directed towards growth. This is an advantage for initial establishment — roots settle quickly if conditions are right — but also a constraint: planting must be carried out in the shortest possible time after delivery, ideally within 24 to 48 hours.

For more detail on the differences between plant types, their delivery calendars and selection criteria by production system: Strawberry plants: cold-stored, fresh or tray plants? →


Quality criteria on delivery: what to check

Delivery inspection is a critical moment that many growers underestimate. A batch of insufficient quality can compromise an entire season without the problem being immediately visible.

Root condition is the primary criterion. Roots should form a well-developed mass that colonises the plug without excessive overgrowth. A plant whose roots have coiled back on themselves — known in the trade as "J-rooting" or root spiralling — will face significant establishment difficulties. If roots are too long at extraction, trimming to 10–15 cm before planting is recommended to prevent them from curling in the soil.

The crown must be firm and well-formed, with one or more crowns visible depending on how early into the season planting will take place. A displaced or over-buried crown in the plug indicates poor management at nursery stage.

Phytosanitary status is non-negotiable. Plug plants are delivered in active vegetative growth, which means they can carry pests or pathogens that are actively present from the nursery of origin. On delivery, systematic inspection of young leaves is essential to detect the presence of two-spotted spider mite, thrips or aphids — pests that can explode in population within days in warm conditions under a tunnel.

For disease, rejection thresholds are strict: any plant showing symptoms of crown rot (Phytophthora cactorum), root rot (Rhizoctonia, Pythium, Fusarium) or crown desiccation must be discarded. These pathogens, introduced into the field with the plants, can establish in the soil and compromise crop rotations for several years.

Ideally, plants are sourced from a CAC-certified supply chain (Conformité Agricole Contrôlée) or equivalent, guaranteeing freedom from virus, nematodes and tarsonemid mites. This is a baseline requirement for a professionally managed crop.

The planting window: every week has a cost


Documented impact of planting date on yield

This is the single most consequential decision of the entire plug plant pathway. And it is where the professional grower has the least room for manoeuvre.

Data from planting date trials conducted by Productions Horticoles Demers in Quebec (Cavendish cultivar, 2003) illustrate precisely what each week of delay costs in terms of yield potential. These trials, conducted on plastic mulch with plug plants, compared three planting dates:

  • 15 August planting: plants developed an average of 3 crowns before fleece application in early October. First-year yields reached 15,500 to 18,000 kg/ha, with an average fruit weight of 11–12 g and a harvest advance of 3 to 5 days compared to uncovered outdoor production.
  • 29 August planting: plants reached only 2 crowns on average. Yields dropped to 10,700 to 17,000 kg/ha depending on the plot, with greater variability.
  • 20 September planting: a single crown per plant, a fraction of the flower trusses of the earlier batches, and yields that collapsed to 3,000 to 4,500 kg/ha. Fruit size remained comparable or slightly higher — but the volume produced does not economically justify the plant investment.

These figures come from a Quebec context that does not translate directly to French conditions. But the underlying logic is universal: the earlier the planting within the useful window, the more time the plant has to develop additional crowns before temperatures shift and floral induction triggers. Each additional crown means additional flower trusses the following spring, and therefore additional yield.

A technical point frequently overlooked: if flower trusses appear in the weeks following planting, immediate removal is recommended. An early autumn crop exhausts plant reserves without commercially viable output, and diverts energy away from rooting and crown development for the following season.


Regional planting windows in France: what the calendar doesn't tell you

The optimal planting window varies significantly by location and production system:

  • Southern regions (Nouvelle-Aquitaine, Provence, Rhône Valley): planting in cold tunnels or unheated glasshouses can extend from August through to early September, with thermal conditions still favourable for root establishment.
  • Northern and Central regions: the window narrows. Under forced tunnels or in open field, planting beyond late August carries increasing risk for root establishment before the first cold.
  • Upland or northern climates: tunnels become near-essential to secure establishment and extend the useful growing season.

The planting date decision is never purely calendrical. It depends on soil condition at the end of the previous crop, current weather, variety choice, and the intended production system. A grower who clears a lettuce crop in early August with a well-drained soil is not in the same position as one who frees their plot on 20 August after a heavily cropped summer.

For detail on planting densities and configurations by system: Strawberry planting: dates and densities →

Establishment and rooting: the critical sequence


Soil preparation and bed formation

Before planting, the soil must be loosened to a depth of 30 to 40 cm. Strawberry has a shallow root system — concentrated in the top 20 to 30 centimetres — and is particularly sensitive to waterlogging in compact or poorly drained soils. In heavy or wet ground, forming raised beds of 10 to 20 cm is recommended to improve drainage and protect the crown from standing moisture, a key driver of Phytophthora.

Plastic mulch — laid before planting with the drip irrigation line installed beneath — serves multiple functions: weed suppression, soil heat retention in early autumn, and fruit cleanliness at harvest. It is the standard support system in most professional plug plant operations.


Planting depth: a mistake with no correction

Plug plant planting follows one non-negotiable rule: the crown must sit exactly at soil surface level. Neither buried nor exposed.

A crown buried just two centimetres promotes heart rot and blocks new leaf emergence. A crown left too exposed exposes roots to the air, leads to desiccation and a highly unpredictable establishment. This millimetre-level precision, during summer planting across thousands of plants, is one of the main sources of within-field heterogeneity observed in first-year crops.


Irrigation protocol for the first 15 days

This is the most demanding phase of the entire pathway. The root system of the plug plant, stressed by lifting and planting, struggles to absorb water in the first few days. Yet planting in August means high temperatures, strong evapotranspiration, and a real risk of rapid desiccation of young roots.

The technical recommendation is as follows:

  • First days: use fine overhead irrigation to ensure soil-to-root contact across the entire planted area. Overhead wetting humidifies the surface and reduces thermal stress on plants.
  • From day 3–5: progressively switch to drip irrigation, with short, frequent applications: 2 to 4 mm per day (approximately 0.3 to 0.5 litres per plant), split across several cycles.
  • Target matric potential: maintain between 5 and 15 kPa in the upper root zone to ensure constant moisture without saturation.

The risk of excess is as real as the risk of deficit. A waterlogged soil creates root asphyxia conditions and promotes Phytophthora crown rot — a disease whose damage often only becomes visible several weeks after infection, when intervention is too late. The target is a soil that is constantly moist, never saturated: drip irrigation, carefully managed, is the only system that achieves this level of precision at field scale.


Runner management after planting

Once plants are established, they can begin to produce runners — particularly in the long-day, high-temperature conditions of summer. These runners divert energy away from rooting and crown development, both of which are the priority at this stage. Systematic, regular removal of all runners produced between planting and dormancy is a crop management task that must not be overlooked.

Nutrition: three phases, three distinct objectives

The most common mistake in plug plant management is treating nutrition as a linear, uniform input across the autumn. Strawberry has nutritional requirements that shift fundamentally between planting and floral induction — and a timing error can cost several weeks of delayed harvest the following spring.


Phase 1 — At planting: drive rooting, not vegetative growth

At transplanting, the sole objective is to promote root colonisation of the soil. A localised application of diammonium phosphate (starter fertiliser) at planting stimulates root system development without triggering premature vegetative growth. Nitrogen must be kept very low at this stage — excessive nitrogen application after planting promotes leaf and runner production at the expense of rooting.


Phase 2 — September/October: supporting rosette development

Once plants are established, from late August to early October, a moderate nitrogen application supports the development of the leaf rosette (5 to 8 leaf stage) and sustains the plant through the active runner production period. Applications remain split and managed, avoiding any excess that would prolong the vegetative phase.

This nutritional management must reflect the actual condition of the plants: a batch that has established well and shows satisfactory vigour does not have the same requirements as one where establishment was difficult.


Phase 3 — Floral induction (October/November): switching to P/K dominance

This is the most critical and least well-documented phase in general agronomic guides. As floral induction approaches — triggered by short days (less than 14 hours of daylight) and temperatures dropping below 15°C, typically between late September and November depending on region — it is essential to reduce nitrogen inputs and shift to phosphorus/potassium dominance.

Fertilisers such as potassium sulphate or monopotassium phosphate take over. The objective is to promote the accumulation of carbohydrate reserves in the crowns, which determines floral potential the following spring.

Excess nitrogen at this stage produces the opposite effect: the plant continues to grow vegetatively, tissues remain soft and susceptible, and sensitivity to Botrytis increases significantly. This is an error that a standardised, non-site-specific nutrition programme cannot detect.

Total crop exports for strawberry are in the order of 52 kg N, 32 kg P and 84 kg K per hectare for a 40 t/ha yield — underlining the structural importance of potassium across the full cycle. In intensive conventional production, a complete programme may reach 120 kg N – 75 kg P – 250 kg K/ha per year, adjusted against leaf analysis.

The P/K switch at floral induction is one of the pivots of this pathway. It is also one of the moments where the assurance of having an expert immediately available makes a real difference — because neither the calendar, nor plant condition, nor weather are the same from one year to the next. Access all our specialist agronomic agents →

Floral induction and winter preparation: setting up next spring's harvest


The floral induction mechanism

For June-bearing varieties — the most widely grown in professional French production (Gariguette, Clery, Darselect) — floral induction is an internal process triggered in October–November, when day length drops below 14 hours and night temperatures settle below 15°C. This induction, invisible to the naked eye, determines the number and quality of flower buds that will open the following spring.

It is not negotiable: if plants are stressed (water deficit, nutrient deficiency, excess nitrogen) when this process triggers, the season's floral potential is compromised — and no winter intervention can compensate for this loss. This is why the entire post-planting pathway — irrigation, nutrition, runner control — must be managed with the objective of presenting plants in full health at this stage.


Fleece or plastic film: two different approaches

Applying a winter cover is near-universal practice in professional production. It serves two functions: protecting plants from early frosts, and providing a thermal advance in spring to shift flowering towards safer temperatures.

Two types of cover are used in France:

  • Non-woven geotextile fleece (P17 or P30 grade): acts by direct covering effect. It limits radiative cooling and maintains humidity at plant level. It provides protection against light frosts (down to -2 or -3°C) and a moderate thermal advance in spring.
  • Thermal plastic film (80 micron, perforated): creates a much more pronounced glasshouse effect, with a thermal advance of +3 to +6°C. This advance is significant in terms of harvest earliness. The trade-off is the need for careful ventilation management: under film, humidity rises rapidly, creating conditions highly favourable to Botrytis and powdery mildew.

The Demers data confirm the importance of application date: fleece applied in early October gives better outcomes than late-month application. The plant benefits from thermal protection during the most active phase of floral induction, and enters dormancy in better condition.

Fleece removal in spring is timed at the threshold of 10% flowering across the plot — too early, and open flowers are exposed to spring frosts; too late, and the heat accumulated under cover promotes disease and desynchronises flowering.

For a comparison of winter management between plug plants, tray plants and cold-stored runners: Tray plant strawberry pathway → and Cold-stored runner strawberry pathway →

Crop protection: risks specific to fresh plant material


A fundamental difference from cold-stored runners

Cold-stored runners are held in cold storage without active foliage at low temperature. When delivered, any pests that might be present are dormant or absent. This is not the case with plug plants.

The plug plant arrives in full vegetative growth. It can introduce active populations of spider mites, thrips or aphids directly into the field from the nursery of origin, without this being visible on first inspection. This is why systematic inspection on delivery is not a formality but an operational necessity.


Priority pests in the post-planting period

Two-spotted spider mite (Tetranychus urticae): the primary threat in August plantings. At 31°C, its development cycle can complete in as little as 7 days, enabling population explosion within a few weeks. On plants still establishing, a heavy infestation slows rooting and weakens plants before winter.

Thrips (Frankliniella occidentalis), whitefly and aphids: monitor from the first weeks under cover, particularly if temperatures remain high.

Botrytis (Botrytis cinerea): under tunnel, the use of overhead irrigation for plant establishment creates high humidity conditions favourable to grey mould development. The switch to drip irrigation must be made as soon as possible to reduce this risk. Effective tunnel ventilation during the day is essential.

Powdery mildew: develops particularly during warm days followed by cool nights with dew — conditions common in September in France. Susceptible varieties (including Gariguette) require close monitoring from establishment onwards.


A preventive programme that cannot be standardised

The general guide that prescribes "one acaricide application at planting and a fungicide every two weeks" does not account for field reality. Pest and disease pressure varies according to regional context, variety, production system, ambient humidity and plot history. A relevant preventive programme is built on regular plant observation and detailed local knowledge — not on a fixed calendar.

From delivery to winter cover: what the technical guide cannot decide for you

A plug plant production pathway accumulates a series of decisions that cannot be made once and for all on the basis of a standard guide. What institutional publications — however comprehensive — cannot do is arbitrate between concrete situations that vary from one farm to another and from one week to the next.

Some examples of questions a professional grower actually faces in August and September:

  • My soil is still warm and slightly dry after the previous crop. Do I plant now or wait 5 more days?
  • My plants show slight heterogeneity on delivery — some have 2 crowns, others just one. Do I accept the batch or reject it?
  • I'm seeing the first spider mite hotspots on 10% of my plants 15 days after planting. Do I intervene now or wait?
  • My geotextile fleece is available from 28 September. Plants look healthy but vegetative growth is still active. Is that too early to apply it in south-west France this year?

These questions demand contextualised answers, grounded in actual phenological stage, local soil and climate conditions, variety, and plot history. This is precisely where specialist agronomic advice adds real value — and where generic technical bulletins reach their limits.

Situational variability is real. The window for correcting a planting mistake is often zero: a plant that fails in August has no second chance. A nutrition programme that misses the floral induction window cannot be corrected in November. A spider mite infestation missed at delivery can spread across an entire field in under three weeks.

Securing every key decision in this pathway — that is precisely the role of Fraisibot, Agronomia's AI agronomist specialised in strawberries, available 24/7 directly on your mobile or tablet, without appointments or travel. Access all our specialist agronomic agents →

Conclusion: a pathway with no margin for error

Plug plants are one of the most powerful tools available for achieving a commercial strawberry harvest in the first year. Their potential is documented — yields above 16,000 kg/ha from mid-August plantings in well-managed systems. But this potential is conditional: it requires a chain of controlled decisions from delivery through to the end of winter.

The plug plant pathway does not tolerate approximation. A planting date that is too late, an irrigation protocol poorly calibrated in the first two weeks, excess nitrogen at floral induction, a missed phytosanitary inspection on delivery — each of these mistakes translates directly into lost yield or quality at harvest. And with establishment costs exceeding €12,500/ha in plants alone, every decision counts.

The complexity of this pathway is not a limitation: it is the reality of professional strawberry production. What you can change is the quality of the technical advice available to support those decisions — and its availability at the precise moment you need it.

Access Fraisibot and secure your crop management decisions from plant delivery onwards. Access all our specialist agronomic agents →

Discover Fraisibot, your AI agronomist specialised in strawberries →

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