Growing strawberries in a polytunnel

Why growers cover strawberries

Strawberries under polythene give three things the open field cannot: an earlier start, dry fruit at harvest and more predictable quality.

An earlier harvest. The UK’s AHDB describes how early covering raises the temperature around the plants and speeds up their development. Tightly closed tunnels usually start fruiting about 14 days earlier than an uncovered crop. For early production, tunnels are put up in winter and covered with film as early as January. AHDB points out that covering before the end of January requires a very strong structure and closer attention from staff.

Protection from rain. According to AHDB, buyers in the UK expect the entire strawberry crop to be picked from under cover. That is why growers cover even older, lower-yielding plantings, sometimes only just before harvest.

Less grey mould. Among the non-chemical methods of limiting grey mould (Botrytis cinerea), the IO-PIB protection programme lists good air movement through the plantation, mulching, drip irrigation and, if the plantation is irrigated with sprinklers, doing so only in the morning. A tunnel with drip irrigation meets these conditions by design: water does not fall on the leaves and fruit.

Single or multibay tunnel

Goal	Tunnel	Why
Very early harvest	single (Solo)	warmer inside; the structure is easy to move to another plot
Large area, low cost per m²	multibay (Multibay)	bays on shared Y-legs, gutters collect rainwater

A single tunnel stands on ground anchors screwed into the soil. For farms that want to get strawberries onto the market as early as possible, it is the natural choice. Multibay tunnels pay off where the area is measured in hectares. You will find indicative prices on the polytunnel prices page.

In the soil or on gutters and table-tops

Growing in the soil

AHDB describes how, in field tunnels, strawberries grow in the soil or in grow bags laid on mulched beds. In the soil, the site matters. IO-PIB recommends that it be free of soil-borne pathogens and pests, including nematodes, and of persistent weeds. At least a year before planting, it is worth growing break crops with a phytosanitary effect: oats, rye, mustard, maize or legumes, ideally in mixtures.

Under cover, weed control works differently from the open field. According to IO-PIB, no chemical herbicides are currently registered for strawberry tunnels. Higher temperatures and the risk of toxic vapours make them difficult to use safely. The basis is mulching with water-permeable materials, such as non-woven fleece, woven ground cover, bark or coarse gravel. Weeds are controlled mechanically or physically, with hot water or a flame weeder.

Gutters and table-tops

Table-top growing originated in the Netherlands and Belgium. AHDB describes it as follows:

• the substrate is always soilless, most often peat, coir or a mix of the two,
• the fruit is picked from plants raised off the ground, so the work is done at working height,
• a raised crop starts fruiting 7–10 days later than strawberries in the soil under the same cover,
• a tunnel over table-tops must have tall sides, leaving room above the plants and a passage for the sprayer.

Gutters and table-tops make the plantation independent of the soil and crop rotation. The ground beneath them still needs mulching. We supply growing gutters together with the tunnel, see growing gutters.

When to plant strawberries under cover

The planting date depends on the type of plants and on when you want to pick. AHDB describes two typical schedules from UK practice:

• Glasshouses and permanent tunnels. Planting from the end of July to mid-August, first harvest after about 60 days. The plants overwinter and fruit again in spring (April–May). So one planting of a June-bearing cultivar gives two harvests.
• Early spring production. In winter, plants prepared earlier in waiting beds are planted out. The tunnel is covered with film in winter, as early as January.

These dates apply to the UK climate.

Whatever the date, IO-PIB stresses one thing: a plantation is established from certified nursery stock. This ensures healthy plants from the start.

Ventilation and temperature in the tunnel

An early strawberry tunnel is a constant trade-off between holding heat in and letting the excess out.

In spring, a tight seal matters. AHDB writes that in early production a well-sealed tunnel is now a priority. Closed doors and side film buried in the ground, or lying evenly against it along the whole length, are essential. Except on sunny days, as much heat as possible should be kept in the tunnel.

In sunshine, ventilate. Ventilation is needed mainly in sunny weather, especially in April. According to AHDB, an extra fleece cover over the plants can bring the crop forward by about 7 days compared with a tunnel without such insulation.

Humidity and disease. Ventilation is also protection. IO-PIB lists good air movement through the plantation, appropriate plant spacing and nitrogen feeding matched to the crop’s needs as the basic non-chemical methods against grey mould.

According to AHDB, large tunnels with a large volume of air warm up more slowly in spring. This is one of the reasons why a single tunnel is more often chosen for very early crops.

A structure for strawberries — what to check

• Type: single for a very early harvest, multibay for a large area.
• Bay width:we build 6–11 m.
• Arch: round or gothic.
• Steel: legs and anchors in E370+Z275 steel (about 10% stronger than S350+Z275, at the same price), hoops in S350+Z275 steel.
• Film: single, 150–200 µm, with a 3-year warranty.

If you cover the tunnel in winter, the structure must withstand it, as AHDB also notes. We will match the configuration on site, at your farm. Start with the configurator or see our strawberry tunnels.