Greenhouses in Zimbabwe: What You Need to Know Before You Buy

Thursday, May 31, 2018

Tomatoes in a greenhouse

Greenhouse farming in Zimbabwe is still relatively small although there is an increased interest in it. The high initial investment of purchasing a greenhouse and the limited availability of financing have limited the growth of greenhouse farming in the country.

With winter approaching you may be exploring ways to extend your growing season and considering getting a greenhouse. Before you make a decision about investing in a greenhouse it's important to understand greenhouse options so you make the right choice to help you achieve profitability.

In this guide, you will learn the definition of a greenhouse, why to grow under greenhouse, what to look for in a greenhouse structure and where to buy a greenhouse in Zimbabwe.


What is a greenhouse?

A greenhouse is a  permanent structure covered with glass or plastic material that allows a farmer to grow crops year-round through partial or fully-controlled environmental conditions to get an optimum growing environment.

A related structure is a high tunnel. Tunnels are also called hoop houses, high tunnels or polytunnels. Tunnels are different from greenhouses in that they are not heated, provide less climate control and are less expensive than greenhouses. Tunnels are temporary structures because they can be easily dismantled for movement.

This guide uses the term greenhouse to include tunnels.

Why get a greenhouse?
  • Growing crops under a greenhouse can provide the ability to protect crops from adverse weather conditions such as heavy winds and unpredictable rainfall due to climate change.
  • Year-round production and supply of fresh vegetables increasing local food supply. This can enable you to get better prices for seasonal crops such as tomatoes that are typically in low supply but high demand during the cool dry season.
  • Increased yields due to the control of the environment. Yields under greenhouse can be 10 to 12 times those of outdoor production depending on the greenhouse and crop type.
  • Uses less water. The use of drip irrigation with shade reduces heat and evaporation and helps cut water consumption by 90%. Control of irrigation amounts is important due to increased droughts.
  • Lower use of nutrients and crop chemicals.
  • Improves product quality and consistency: less damage to crops increasing the fruit quality.
  • Good for seedling production: growing seedlings provides an alternative source of income. Seedlings are more productive under greenhouse than open-air production. 
  • Protection against some pests and disease: greenhouse with good design can help reduce pests. It also keeps rainfall off leaves reducing leaf diseases.
  • Space efficient: ideal for urban farmers with limited space.
Drawbacks
  • High upfront and operating expenses.
  • High relative humidity in the greenhouse can create conditions favourable to some fungal and bacterial diseases. 
  • High temperatures can be detrimental to plants and can result in reduced crop performance
What crops you can grow in a greenhouse

The main crops currently grown under greenhouse in Zimbabwe are tomatoes, cucumbers, bell peppers and nursery plant materials for the local market. In the past greenhouses in Zimbabwe, such as in Ruwa where we farm, produced cut flowers such as roses for export to Europe. Reviving flower exports will require investments in greenhouses to protect delicate flowers.

Research and choose carefully what crops to grow in your greenhouse to get a good return on your investment. Factors to consider are price, market demand, climate, skills and knowledge. Crops with good returns will help you pay off your investment in fewer grow cycles.

Greenhouse Designs

They are many design options to choose from ranging from attached (lean-to), freestanding (Quonset, even span, uneven span) and gutter connected (sawtooth).
  • Freestanding greenhouses: can have a Quonset, gothic or gable-shaped roof. These are suitable for small-scale commercial farmers as they are less expensive. Designs include high tunnels.
  • Gutter-connected greenhouses: a series of gables or arches connected together at the gutter level. It provides more growing space and offers the greatest flexibility, efficiency and economies of scale. 
Free-standing styles are more common in Zimbabwe though you also find gutter connected designs from companies such as Greencon.

Structural Material/ Frame Options

The type of construction is influenced by the structural material which supports the greenhouse structure. The main structural materials are wood, steel, aluminium, and PVC.
  • Wood Frame: wood frames have a low initial cost but maintenance is high and they are flammable. If not treated they are vulnerable to termites and wood rot. It is important to choose treated wood. Wood is less durable and strong than metal. 
  • Metal Frame:  galvanized steel or aluminium frames are the strongest structural materials for a greenhouse. They are the preferred materials for construction because they last longer, are stronger and need less maintenance. The drawback is that plastic film breaks down more rapidly when it comes in contact with hot metal.
Choose a steady structure with strong construction to avoid it collapsing under heavy rain, equipment in the structure or getting blown away by any heavy winds.

Greenhouse Covering Material (Glazing)

The covering material is a very important component of the greenhouse structure. The material has a direct effect on the greenhouse effect inside the structure and can alter the temperature inside.

Types of greenhouse coverings:
  • Net house: this is a good option if funds are limited. It is the simplest and cheapest option. It provides shade and protects against insects. The drawback of this structure is the permeability of rainfall and low light penetration which affects plant growth. It is typically used for seedlings, shade plants and ornamentals. 
  • Plastic glazing: offers better protection against rainfall and makes more light available to the crops. Yields are higher than a net house. Good ventilation is important to protect plants from high temperatures. Ventilation can be done manually or mechanically where electricity and capital are available. Types of plastic film coverings include polyethylene (PE) film and polyvinyl chloride (PVC) film, though polyethylene is more common in commercial greenhouses. UV resistant coated plastic and light transmission are important considerations. 
  • Glass glazing:  Provides the best light transmission for greenhouse production. It has long lifetime but is very expensive. Choose this option if profitability is high and you have access to capital to make the high initial investment.
Ventilation
Temperatures can get high in the summer months in Zimbabwe especially in the Lowveld, therefore good ventilation is important for plant growth. Poor ventilation can have a negative effect on crop photosynthesis and plant growth.
  • Natural ventilation: relies on the natural air movement for cooling the greenhouse. Good ventilation is important for optimum plant growth. Naturally ventilated greenhouses are more cost-efficient than mechanically cooled structures. They are the only option if you do not have regular electricity. Small greenhouses can use natural ventilation, however, larger greenhouses may need mechanical ventilation to avoid high temperatures in the centre. Consider the ventilation openings for natural cooling this can either be top ventilation or side ventilation depending on the wind direction.  
  • Mechanical Ventilation:  Mechanical cooling such as using circulation fans requires stable electricity and is not always cost-effective because of high energy costs. Useful if alternative energy sources are available because provides better temperature control.  Circulation fans can be placed in a greenhouse to stimulate air circulation and create a homogeneous climate and crop transpiration. Other mechanical ventilation options are fan and pad cooling and fogging systems.
Watering

Water is essential to farming including greenhouse farming. Automated drip irrigation is better than hand watering for greenhouse farming, though hand watering is cheaper. The simplest form is gravity-based. A tank is placed a few metres high and gravity ensures that water is drip irrigated to the plants. Drip irrigation allows you to apply water and nutrients (fertigation) in the proper quantities and at the right times.

Crop Protection

The level of pests and diseases are high in Zimbabwe. Openings of the greenhouse can be covered with an insect screen to prevent pests entering the greenhouse. When screens are used ventilation needs to be carefully considered because it can affect air circulation. Poor air circulation causes decreased yield and quality. Other means of crop protection may be necessary.

A sluice construction with a double door is generally better than a single door. A single door does not block insect entrance if the door is opened.

Screens

Shading screen: A shade screen/cloth is used to protect young plants from exposure to the blazing hot sun (temperature and light intensity) depending on the shading material.

Thermal screen: used to preserve heat in case of low (night) temperatures

Size of Greenhouse

A greenhouse is a long-term investment and the size must be adequate for many years to come. Consider future growing needs when deciding on the size of your greenhouse. Another important factor when considering size is profitability. To achieve profitability you need a greenhouse that can hold more plants. The minimum size for profitability is about 1,000 m2 because of the improved economies of scale.

Choosing a Greenhouse Provider

Some suppliers will quote just the greenhouse alone and not include other costs such as the water tank, drip lines and seed. Others will quote the total price inclusive of installation costs. Make sure you understand what is covered when comparing costs so you can compare apples to apples and don't get surprised by additional costs.

Understand that the true cost components of a greenhouse. Cost considerations include not just the structure but also the borehole ( if you don't already have one), irrigation, staff salaries, utilities, maintenance, transport and installation.

Other factors to consider when choosing a supplier is the technical support and other services they provide.

Several companies offer greenhouse construction services. Including:
  • Greencon: 8 Coronation Avenue, Msasa/Greendale, Harare. Tel:  0773 141 273 Web: http://www.greencon.co.zw
  • Pedstock: Corner Harare Drive/ Alpes Road, Vainona, Mt. Pleasant, Harare. Tel: +263-4851687/90
  • Total Farm Solutions: 3 Monmouth Road, Avondale, Harare. Tel: (263) 778397546. Email: sales@tfs.co.zw. Web: http://www.tfs.co.zw
  • Brown Engineering Group: 17 James Martin Ave, Lochnivar, Southerton, Harare. Tel: +263 4 664795-8. Email: sales@be.co.zw
  • Agristructures: 74 Gleneagles Cnr Woolrich Road, Willowvale, Harare. Tel: +263-7122221207
Picking the right greenhouse and materials is dependent on a number of factors including crop requirements, climate (temperature and rainfall), greenhouse size, electricity, market, produce prices and budget. Your greenhouse structure should be structurally sound to withstand environmental elements and internal loads. It should also provide good ventilation to your crops. If you get it right you could be producing high yields year round.

We want to hear from you. Let us know in the comments if you have a greenhouse or are considering or not considering getting a greenhouse.

4 comments:

  1. Replies
    1. Yes you can grow cucumbers in a greenhouse. The market price for cucumbers in Zimbabwe is not always good, so it helps to check on that first.

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  2. Hi. Thanks forthe article. I am considering greenhouse farming. Doyou have a video for step by step installation of a greenhouse?

    ReplyDelete
    Replies
    1. Hi. No we don't have a video on greenhouse installation. Do a search on Youtube you should be able to find some videos on the step-by step of installing hoop houses (tunnels).

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