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Tunnelhouses

Why?

Why use crop protection structures?
Growers use structures to protect crops for the following reasons –

• to extend the growing season
• to mitigate fluctuations in temperature and humidity
• to grow crops with a higher heat requirement than provided by the local climate
• to mature crops more quickly
• to produce crops ‘out of season’

Essentially structures modify the climate and allow the grower greater certainty of yield.

Where

There are three things needed for successful horticulture in Canterbury; shelter, shelter and shelter. Your crop protecting structure can provide the last two of these but itself needs shelter from wind.
Shelter from the wind will reduce the wear on the cover and reduce the cooling effect due to airflow. Some tunnelhouses have been tested under rigourous conditions and have yet to fail.

Options

Design, Shapes and Sizes.
‘Tunnels’ begin with hoop cloches. Cloches are a cheaper option than tunnelhouses for covering crops. They can be left open on the leeward side (closed again in evenings in cooler temperatures) to improve ventilation. Cloches are easily relocatable. They are best used for facilitating early production.

Floating row covers could be explored as an option for reducing pest problems. The lighter grades are okay to just rest on the top of the crop and can exclude pests. The heavier grades are required for improving temperature and will require hoops to keep them off the crop plants.

Tunnelhouses require a greater capital outlay but are more user friendly than cloches. The advantage of the tunnelhouse approach is to have a walk in protected environment. Full plastic cover over the winter gives better temperature profiles than a cloche. It also provides a protected environment for working in inclement weather and crops can be accessed easily. Portable tunnelhouses have the great advantage of allowing rotation of soils for less disease problems and greater versatility. Sides can be replaced with windbreak especially in summer conditions - to improve ventilation and reduce high temperatures. Tunnelhouses should be located in a sheltered area. If wind is a problem the windward side should remain fully covered with plastic film.

Tunnelhouses eliminate rainfall, lowering the potential for fungal diseases if they are adequately ventilated and irrigation is by drip tape. They can also be useful for excluding insects and other pests. There may be scope to use meshing lined houses rather than plastic film and this could be investigated in the future. Such systems are common in South Asia for insect pest control.