Highbush blueberries under cover
Cover protects blueberries from rain during flowering and harvest, when, according to IO-PIB, grey mould can cause significant yield losses. In a University of Florida research review (2020), southern highbush cultivars under cover ripened almost a month earlier than in the open field.
Why cover highbush blueberries
Blueberries are a perennial bush, and a plantation is an investment for many years. Cover will not replace good crop husbandry, but it reduces several risks that have no simple answer in the open field.
Rain during flowering and harvest
The integrated protection guidelines for highbush blueberry from IO (Instytut Ogrodnictwa, the Polish horticultural research institute) describe grey mould as a highly damaging disease, especially in years with a lot of rain during flowering and harvest. It can cause significant yield losses. Anthracnose is described in a similar way: highly damaging, especially in wet years.
A tunnel with drip irrigation keeps water away from flowers and fruit. IO recommends drip irrigation on intensive plantations. If the plantation is irrigated with sprinklers, it is best done in the morning so that the leaves dry quickly.
Fruit splitting
The IO-PIB recommendations on blueberry storage (2023) list fruit splitting, alongside shrivelling and sunscald, among the disorders that can cause the greatest losses. The same recommendations name unfavourable weather during the season as one of the serious problems growers face.
Research by the USDA and the University of Southern Mississippi (HortScience, 2007) showed that rain falling on ripe or nearly ripe fruit before harvest can cause splitting. Field observations over many years showed that susceptibility depends greatly on the cultivar. The study covered rabbiteye and southern highbush blueberries, not the northern highbush cultivars that dominate in Poland.
Frost and an earlier harvest
A University of Florida research review (Fang et al., 2020) concludes that the tunnel microclimate:
- brings forward flowering and fruit ripening,
- can improve yield and fruit quality and extend the picking season,
- reduces fruit losses from rain and frost.
In the studies cited, the cultivars ‘Snowchaser’, ‘Emerald’, ‘Jewel’ and ‘O’Neal’ in tunnels were ready to pick almost a month earlier than in the open field. These are southern cultivars in a warm climate.
The same review warns that an unheated tunnel is not always enough to protect against frost during flowering. Growers in the USA then also run sprinklers over the plants inside the tunnel. In the open field, IO-PIB describes frost-protection sprinkling, which can protect flowers even when the temperature drops to −5°C.
What to watch under polythene
Heat. According to the University of Florida, air temperatures above 30°C reduce blueberry photosynthesis, and warm nights (21°C) can reduce fruit set. Tunnels are usually ventilated from about 10°C. Without automatic roll-up sides, this is done by hand.
Pollination. Honeybees are most active at about 20°C and may work less well in a warm, closed tunnel. The University of Florida suggests two solutions: sides that open, or bumblebee hives placed in the tunnel.
Pots or soil
| Soil requirements | acidic soil rich in organic matter | independent of the soil on the plot |
|---|---|---|
| Substrate | soil improved before planting | peat, coir, perlite, in mixes |
| Irrigation | drip or sprinklers | drip, doses adjusted to drainage |
| Risks | soil-borne diseases, unsuitable pH | fluctuating substrate temperature, bushes blown over by wind |
The University of Florida describes container growing as a way to produce where the soil is unsuitable. It allows precise control of nutrition and avoids soil problems. In central Florida, containers of 56–95 l were typically used. Containers smaller than 38 l reduced yield. Bushes in small pots can blow over in strong wind and need support.
A Slovenian team from the University of Ljubljana (2022) compared growing in pots and on ridges under tunnels. Substrate moisture was similar, but the temperature in the pots fluctuated more. Growth of ‘Duke’ and ‘Aurora’ bushes was weaker in pots. ‘Aurora’ yielded less in pots, ‘Brigitta’ more. The authors considered pots a useful method for ‘Duke’ and ‘Brigitta’.
Conclusion: the choice of system depends on the cultivar and conditions on the farm.
Tunnel height and the bushes
A blueberry tunnel stands over a perennial bush. So you need to allow for the height of the mature bush, not the young plant, plus room for picking and for machinery to pass. IO-PIB gives these spacings:
- for hand picking on poorer soils, 2.5–3.0 m between rows and 0.8–1.0 m within the row,
- on larger plantations, 3.0–3.5 m between rows and 0.8–1.2 m within the row,
- for machine harvesting, 3.5–4.0 m between rows.
The bay width is therefore chosen as a multiple of the row spacing. We build bays 6–11 m wide and tunnels up to 5 m high on upset anchors (1.25–2.0 m).
Multibay tunnels for larger areas
For plantations measured in hectares we recommend multibay tunnels:
- bays joined on shared rows of legs (Y-legs screwed into the soil, 2.5–3.5 m),
- gutters and rainwater collection,
- a lower cost per m² than with single tunnels, prices on the polytunnel prices page,
- legs and anchors in E370+Z275 steel, hoops in S350+Z275 steel, round or gothic arch,
- single film 150–200 µm with a 3-year warranty.
A single tunnel is warmer inside and easy to relocate. It works well for very early crops and on smaller plots.
We match the configuration on site to the row spacing and the harvesting method. Start with the configurator or see blueberry tunnels.
Sources
- Metodyka integrowanej ochrony borówki wysokiej (materiały dla producentów, poprawki 2022) [Integrated protection of highbush blueberry — guidance for growers, 2022 revision], Instytut Ogrodnictwa, Skierniewice (accessed 11 October 2026)
- Zalecenia technologiczne dla przechowywania i transportu borówki wysokiej [Technical recommendations for the storage and transport of highbush blueberries] — K.P. Rutkowski et al., Instytut Ogrodnictwa – PIB, 2023 (accessed 11 October 2026)
- A Review for Southern Highbush Blueberry Alternative Production Systems — Y. Fang et al., Agronomy 2020, 10, 1531 (University of Florida) (accessed 11 October 2026)
- Laboratory Method to Estimate Rain-Induced Splitting in Cultivated Blueberries — D.A. Marshall-Shaw, J.M. Spiers, S.J. Stringer, K.J. Curry, HortScience 42(7), 2007 (accessed 11 October 2026)
- Pot and Ridge Production of Three Highbush Blueberry Cultivars under High Tunnels — T. Smrke et al., Agriculture 12(4), 2022 (University of Ljubljana) (accessed 11 October 2026)