What is a greenhouse and how does it work?

A greenhouse (also known as glass house or hot house) is a structure covered predominantly by a transparent material like glass or plastic (rigid panels or polythene). Greenhouses are used to grow crops that require or that can benefit from an enhanced and/or regulated micro-environment. Greenhouses are used to enhance the rate of growth and productivity of such crops.

The greenhouse covering (polythene, glass etc) admits light into the greenhouse. Light rays that enter the greenhouse are absorbed by plants and other objects and converted to heat which warms the greenhouse such that the greenhouse remains consistently warm. The activities in the greenhouse enhance the rate of photosynthesis and hence plant growth. Technically speaking, greenhouses convert solar energy to thermal energy. Excess heat in greenhouses can be allowed to escape through side windows and vents since heat cannot move through the covering material as light does. The structural framework of a greenhouse can be made of steel, wood or plastic.

Greenhouses in Kenya are used for hobby gardening, kitchen gardening for domestic consumption, commercial production in small, medium and large scale and for production of export vegetables, flowers and herbs. Hydroponics and fish production under greenhouse environment is also becoming increasingly popular.

Small and medium scale farmers in Kenya use structures known as tunnels which are simplified greenhouses with little or no climate control systems, no fertilizer application equipment for fertigation or injection and  no or minimal automation. In tunnels, fertilizer is applied mostly by top dressing, foliar spraying or through the drip system; excess heat escapes through the side and/or roof vents and water application is largely guided by day to day judgment of the greenhouse caretaker. More sophisticated greenhouse operations incorporate thermometers, moisture sensors, artificial heating and cooling systems, sophisticated fertigation or injection systems and many times fertilizer and water application is automated and strictly monitored.

Advantages of greenhouses

  1. Faster plant growth.
  2. Longer harvesting period that can exceed six months (only possible with the correct varieties – indeterminate varieties).
  3. High production per unit of land.
  4. Ability to stagger production and subsequently time the high season.
  5. All year round production can be achieved since there is relatively low dependence on prevailing weather circumstances.
  6. Relative protection from pests and other physiological conditions like hailstorm, excessive rainfall and excessively cold temperatures.
  7. Ability to farm in areas that would otherwise not be suitable for the desired crop.


  1. High initial cost of greenhouse infrastructure set up.
  2. Greenhouse management requires a higher level of crop management skill as compared to open field production. It is important for first time greenhouse farmers to get proper guidance at least for one season.

Popular Greenhouse Crops

Most crops can grow and thrive under greenhouse conditions but it is important to identify those that give highest return on investment within the shortest time possible. The following are popular greenhouse crops in Kenya:

  1. Tomatoes.
  2. Coloured and green capsicum (Hoho).
  3. Cucumbers.
  4. Herbs.
  5. Flowers (Grown predominantly by large scale farmers for export).
  6. For purposes of rotation and to give the soil a break, indeginous vegetables like cowpeas (kunde) and spider plant (sagaa or saget) can be planted. Sukuma wiki and spinach can also be considered.

Determinate versus Indeterminate crops

Determinate varieties of crops grow for short periods of time and typically stop growing once they have produced fruits and flowers. Such crops are harvested for short periods of time, say one or two months then they become unproductive. Determinate crops are best for open field production. Production of such crops is enhanced with irrigation.

Indeterminate crops grow for long periods of time and are less bushy as compared to determinate crops. They continuously produce fruits and flowers so long as they are healthy. Indeterminate greenhouse crops like tomatoes and colored capsicum can be harvested for 6-12 months with proper management and nutrition. Such crops give better value for greenhouse farmers and it is therefore generally accepted practice and much more prudent to grow indeterminate crops in greenhouses.  Indeterminate varieties have long weak vines that require support.  Examples of Indeterminate tomato varieties include: Tylka F1, Anna F1, Eva F1, Corazon, Bravo and Chonto while capsicum varieties include Red Knight, Passarela, Commandant, Illanga, Admiral and Golden sun.

Seedling Germination

Germination is normally done using artificial growing medium like hygromix in special germination trays. Tray germination has several advantages over soil germination:

  1. Uniformity of growth.
  2. It is easier to protect the seedlings from early contamination.
  3. It is easier to provide nutrition in tray nurseries.
  4. Additional seedlings can be planted for gaping with only the strongest seedlings being selected for initial crop establishment.

Common Diseases, Insects and Disorders in Greenhouse Production

·         Cut worms ·         Powdery Mildew ·         Blossom End Rot
·         White flies ·         Bacterial Wilt ·         Sun scald
·         Tuta Absoluta ·         Fusarium Wilt ·         Fruit Cracking (Radial & concentric)
·         Thrips ·         Anthracnose ·         Cat facing
·         Mites ·         Blight ·         Leaf yellowing
·         Aphids ·         Bacterial specks  

These threats are largely manageable but one must anticipate and prepare for them. Crop protection in greenhouses involves good nutrition, timely application of agrochemicals when necessary and integration of non-chemical control methods. Good sanitation and crop management practices are also vital in maintaining proper plant health. We encourage farmers to incorporate non-chemical control techniques in their crop protection programs.

Success Factors

  1. A proper greenhouse structure and irrigation system to begin with.
  2. Proper soil preparation and management including soil testing and addition of adequate quantities of organic matter.
  3. Use of strong, healthy seedlings.
  4. Disease and insect control.
  5. Proper and timely application of fertilizers which could be soil based, foliar based or water based (fertigation).
  6. Good quality of irrigation water with timely and adequate application.
  7. Good and timely crop management – weeding, trellising, pruning, removal of suckers etc.

Market for Greenhouse Crops

Greenhouse farmers in the past have faced some resistance from potential markets due to misconceptions about greenhouse produced crops. However with increasing understanding of the greenhouse concept, greenhouse produced crops are slowly gaining an edge over open field crops with a good number of outlets showing preference for greenhouse crops. Farmers have also learnt how to take care of greenhouse produced crops and are increasingly producing better quality crops that are hugely popular with consumers. A good crop should have a uniform attractive colour, sweet taste, good size, firm strong skin, thick flesh and a long shelf life.

Potential outlets for greenhouse produced crops include neighbours, colleagues, institutions like schools, restaurants, hotels and hospitals; greengrocers located in almost every mall (Zucchini, Westlands Grocers, New Muthaiga Greengrocers, Kalimoni Greens etc), vegetable distributors like Fresh and Juici, open markets like Ngara Market, Marikiti and Citipark market, car boot roadside sale, own grocery shop etc. The export market can also be tapped but requires that one pays close attention to international standards. Market is only limited by one’s imagination. Value addition and preservation is encouraged.

Misconceptions about Greenhouses.

  1. Greenhouses are pest free, risk free environments – Greenhouses have been largely sold in Kenya as pest and risk free environments that guarantee high returns with minimal effort. Whereas the greenhouse environment provides a fairly protected micro-environment which makes it easier to control weeds, insects and diseases and therefore achieve significantly higher yields, it is still important to take precaution against pests and other risks if one is to make good returns. When production commences an integrated pest control program should be implemented alongside a nutrition or feeding program informed by a soil fertility test.
  2. Greenhouses cause greenhouse gases – Greenhouses are NOT named as such because they are responsible for producing greenhouse gases. On the contrary, a greenhouse is a safe, peaceful and relaxing place to work if well tended to. Many urban greenhouse farmers have lighting systems inside their greenhouses that allow them to work and unwind in their greenhouses after working long hours in confined spaces. Perhaps the simple explanation for the name ‘greenhouse’ is that most plants are green and therefore a structure that ‘houses’ them would simply be referred to as a greenhouse. Technically, the greenhouse micro climate works in an almost similar way as greenhouse gases do. Just like greenhouse gases let sunlight through but subsequently trap the heat that comes with the light in the atmosphere preventing excess heat from escaping as they should, the greenhouse cover also allows heat through then traps most of the excess heat that would have otherwise escaped. This keeps the greenhouse environment consistently warm allowing heat loving crops to thrive. Light an important ingredient in photosynthesis is also enhanced and this enhances the rate of greenhouse plant growth and productivity.

The primary greenhouse gases responsible for global warming are Carbon dioxide (CO2) produced largely from industries, Methane (CH4) emitted by livestock, from wetlands and coal mines, Nitrous Oxide (N2O) released from some factories and some fertilizer, Chloroflourocarbons (CFCs) which are flourinated gases not produced in nature and Water vapour. These gasses are NOT emitted from greenhouses.

Source of Greenhouses, Irrigation systems and Inputs

There are a number of companies that provide greenhouse construction services in Kenya but we pride ourselves in providing value at an affordable cost. We offer an end to end solution that starts with a reconnaissance survey of the site, project planning, management of the project and market linkages. We highly recommend that you try our services.

Is Greenhouse Farming a lucrative venture? Yes. But just like any other business, it takes planning and hard work.

Clifton Opala is the Founder and Director of Ace Intergrated Services. We are an agricultural services firm that is passionate about small holder farmer empowerment, food security and environmental conservation. Our services include Greenhouse Construction & Management, Irrigation Systems Design and Installation, Farm Set up & Management and Construction of Farm Structures.

Tel: +254-721-681943

Facebook: @aceagriculturekenya



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