Spanish Tunnels

Spanish Tunnels, also known as high tunnels or hoop houses, can effectively be described as inexpensive "large walk-in plastic tunnels".

Spanish Tunnels were originally designed and developed in the Pointe de Almeria region on the Mediterranean coast of Spain in the 70’s and 80’s for the crop protection of table grapes as part of their government’s rehabilitation program of the (then) poorest region of the country.

Along with adding phenomenal amounts of topsoil and manure to the barren land and embarking on extensive water volume and quality projects, they poured vast resources into the development of beneficial crop protection and finally settled on, what is today aptly named, the Spanish tunnel.

Although the table grapes have since en large been replaced by other products, Almeria remains one of the world’s largest producers of fresh vegetables and fruit destined for export markets.

The UK, in particular, has been quick to spot and embrace the merits of Spanish style crop protection – an estimated 75% of all crop protected products is at present being grown under Spanish tunnels.

Composition

Spanish tunnels consist of a light yet strong web of legs, hoops, strut-ends, wire, rope, plastic film, clips and clamps. 6,5m and 8m bay-widths are standard, however custom designing is available to meet grower instructions and specifications.

The 2,2m long “Y”-shaped legs have helix anchors at their bases for screwing into the soil – usually to a depth of between 500mm and 1m, depending on weather and soil constraints. The legs are staggered 2,2m apart.

The hoops are rolled into a true arc to maximize structural strength and are slipped over the top-ends of the legs. The height of the apex of the arc is between 4m and 4,5m. To minimize material usage, the internal legs are shared between two hoops, adding to the web-like strength.

The ends of each tunnel-bay are reinforced by a set of strut-ends, fastened onto the legs and hoops using convenient hinged clamps.

High strain steel wire is connected between the strutted ends and fastened onto each hoop using potato bag ties (a solid steel tube “ridge pole” is an optional variation). The wire is tensioned, placing the entire structure in a sturdy state of equilibrium between the compressed strutted ends.

180 or 200 micron clear or diffused plastic film is then pulled over the top of the bays and securely attached to the ends using spring clips. Monofilament polypropylene rope is then strung over each hoop section in a crossing over fashion and tied to the rope hooks provided on each leg.

WET ZA post manufacture, hot-dip galvanize all their steel components and ensures that all plastics are UVI treated.

Crops that benefit

Raspberries (click on thumbnail to view larger picture)

Strawberries (click on thumbnail to view larger picture)

Plums Blue berries

Cherries Red currants

Nurseries Pot plants

Herbs Peppers

Table Grapes Cut Flowers

Blackberries Blueberries

Melons Any other high value crop

Who uses tunnels?

On browsing the internet we discovered some interesting statistics with regards to tunnel usage within the world’s agricultural sector: in Spain, almost 100% of their soft fruit crops are protected under tunnelling, 90% in France and Belgium and more than 80% in the Netherlands. Within the European market it seems that there is no longer a debate whether to cover a crop or not, but rather which material to choose for what effect!

The South African market has, however, been slow on the uptake of incorporating tunnels into their farming processes, with cost being the major stumbling block. The introduction of the Spanish-style multi-bay tunnels (which are sold by WET ZA) to the South African market are, however, more cost effective than the conventional, individual 30x10m permanent structures.

Advantages of using tunnels

Longer Season – typically 2-3 weeks earlier than outdoor production, consistent and extended autumn production

Improved Product Quality – substantially higher first class product compared to outdoor production

Increased Yields – first class yields often 15-20% higher under tunnels

Weather Protection – reduced risk of damage due to wind, rain, heavy dew, sand, hail, frost and excessive sun

Improved Production Management – removes weather dependence for picking and crop maintenance

Less Disease Pressure – with rain and dew eliminated, Botrytis and anthracnose risk is diminished

Reliability of Supply – delivery on yield estimates and customer expectation

Accessible to Machinery – same equipment is employed as in open field

Tunnel management

To minimise the potential weather relted risk to both your crop and your tunnel structures, these guidelines can be followed:

Structure

We suggest two stages of venting:

1. Winds between 55 & 65km/h (34 & 40mph)

Vent halfway without loosening ropes

2. Winds exceeding 65km/h (40mph)

Move poly to top position and secure with tie-down ropes

We also suggest to take caution with tunnels longer than 100m and to take a further 5km/h (3mph) off suggested wind speeds.

These guidelines may vary with the quality of tunnel construction. Please consult your adviser/agent for advise.

Crops

Manage the tunnel temperature and humidity by venting the tunnels if the temperature exceeds 23 degrees Celsius. In extreme heat conditions vent tunnels all the way to the top position. These limits may vary between crops, so please consult your agronomist or tunnel agent for advise relevant to your crop.

Cost

For your free quotation, please contact Anthony or Peter at Well*Pict European Tunnels ZA. We pride ourselves in tailor-made solutions for your growing needs.