Pros and Cons of Growing in Tunnels

Now that winter is here with icy winds and frost, smallholders with tunnels will be glad of the ability to protect their vegetables.
A tunnel has a frame made from steel or plastic, which is covered in clear polyethylene sheeting or shade cloth. Tunnels are usually semi-circular, square or elongated in shape. The interior heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building faster than heat can escape the structure. Air warmed by the heat from hot interior surfaces is retained in the structure by the roof and wall. Temperature, humidity and ventilation can be controlled by equipment in the tunnel or by manual opening and closing of flaps along the sides of the structure.
In addition to growing vegetables and flowers in tunnels, more smallholders are showing an interest in aquaponics for Tilapia fish farming in tunnels.
There are many obvious pros to growing in tunnels. You have an extended growing season and can grow a greater variety of vegetables in winter. Sometimes there will be faster after crop growth and higher total yields and your vegetables will be unblemished because they have not been battered by the elements.
It is very pleasant in winter to work in a tunnel and it is cheaper than a heated greenhouse.
However, depending on the size of the tunnel, your start-up costs can be considerable. Unless you want to grow vegetables commercially, most smallholders will not be able to justify the expenditure. Even if you do not invest in a great deal of climate-control equipment, you will still have to maintain the structure.
Tunnels are vulnerable to hail and wind damage and the plastic will have to be replaced every few years because of sun damage.
If you want to establish a tunnel business it might be possible to receive funding from entities such as Gauteng Enterprise Propeller (GEP) and the Gauteng Dept of Agriculture & Rural Development. Sometimes municipal agricultural departments also supply tunnels to qualifying smallholders.
There are various designs of DIY kits available and one can also buy them second hand.
Ventilation is an important factor to get right. A common way to ventilate is to have roll-up sides. It’s the only way of keeping the tunnel from getting too hot during the day in the spring or summer or even in other months of the year.
Growing in protected culture requires greater attention to detail. You need to monitor your plants constantly, because the warmer conditions that favour your plant growth are also good for certain insects and diseases. Aphids, white fly, some thrip and spider mites can be problematic. Companion planting should include plants that host beneficial insects.
Tunnels do reduce some diseases but exacerbate other diseases. Tunnels create micro-climates and disease can spread fast. Depending on the vegetables you are growing, you need to guard against powdery mildew and botrytis, Verticillium and Fusarium wilts and, depending on the area, bacterial wilt. Increase air flow, reduce humidity and use disease-resistant varieties to help manage these diseases.
Viruses can also be a problem. Disposable gloves, regular hand washing and tool disinfection will reduce the spread of viruses and other systemic diseases.
Narrow aisles require careful attention to crop canopy management, so pruning and trellising are might be necessary.
Irrigation management requires greater care. Know when to increase irrigation flow to maximize plant growth, but also know how to avoid root rot.
If you are not using any form of heating, do not think that you are going to grow summer vegetables such as tomatoes in your tunnel during winter, because it just won’t get hot enough.
In fact, many tunnel farmers in the colder areas will cease production in the coldest months, using the time to perform maintenance and repair tasks.

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