Why Coast green house farmers are going for shade nets

The ongoing dry spell in several parts of the country has brought untold suffering to farmers at the Coast.
Several wells have dried up, leaving crop and livestock farmers with no water for irrigation or to offer their animals.
However, it is the greenhouse farmers in the region who are finding the going tough as temperatures in the region average 34 degrees Celsius.

Sr Lydia Makori, who grows tomatoes in Mtwapa, Kilifi County in greenhouses, says this year’s temperatures are too high, a situation that has made greenhouse farming nearly impossible.
“We were forced to abandon greenhouse plastic film for shade netting after our tomatoes and vegetables started to wither,” says Makori, who belongs to the Sisters of Mary Mother of God, Mombasa.
The nuns have been farming in greenhouses since 2016 and initially, they had no problem until temperatures started to rise.
“We had no choice but to replace the plastic films with shade nets. When we were using greenhouses, our vegetables were yellowing, or withering most of the time,” Sr Makori says.
According to her, the shade nets are better as compared to greenhouse materials because they allow good air circulation.

Replacements of greenhouses
Universal Farm Experts director Cosmas Kamicha says at least 12 farmers in the region have sought their help to replace greenhouse materials with shade nets, with places like Malindi being worst affected.
According to him, most farmers with greenhouses at the Coast have been getting poor harvest due to the high humidity.
“Farmers are realising that with the rise in temperatures, plastic films cannot work well at the Coast. These structures need good regulation of temperature which is hard to achieve in a greenhouse with few windows unlike shade nets,” Kamicha says.
He notes that the purpose of greenhouses is to reduce insect and disease infestation as crops grow in a controlled environment.
“But if one is forced to open all the windows on a greenhouse due to high temperatures, then pests get in, defeating the purpose.”
Paul Kisiangani, a horticulturalist at the Agribusiness Youth Society of Kenya, says one of the considerations when installing greenhouses is regulation of the crop climate.
“Some of the greenhouse papers may not be factored for a particular climate. At the Coast, one needs greenhouse cover that does not accumulate excess heat because a higher temperature affects the growth of any plant and gives rise to pathogens, affecting productivity,” Kisiangani says.
According to him, shade nets are most appropriate because they filter solar radiation and provide a near normal environment for plant growth.

Quantity of light
He explains that shade nets are made in terms of solar filtration capacity and most of them range from 60 to around 90 per cent filtration, meaning they can reduce the quantity of light or heat that goes through the structure.
“When the temperatures in the greenhouse go above 40 degrees Celsius, this affects the growth of the plants. Soil moisture is affected by temperatures within the green house. The higher the temperature, the more the soil moisture drops due to evaporation and this results in wilting of the plants,” says Kisiangani.

According to him, if outside temperatures are about 34 degrees Celsius, in a greenhouse, temperatures will range between 35 to 45 Celsius on average.

“But this can rise depending on the season and the ventilation of the greenhouse,” Kisiangani adds.
He advises farmers to understand climatic and environmental conditions a particular crop requires before investing in greenhouse structures.