If winter is dragging on, but you just can’t get away, here is a chance to see other parts of the world from the comfort of your own office or home. Please join us, as we share our greenhouse observations with you in a series of articles for Greenhouse Canada. Both of us have had the wonderful experience of being involved with the Canadian horticultural industry for many years. Now we are working with horticulture on a global scale. In our positions with the International Division of Plant Products Co. Ltd., we travel the world providing product and technical support for Plant-Prod and Plantex fertilizer sales. This has given us the opportunity to see many different countries, crops, growing techniques and growing conditions.
|Small doorway into greenhouse through mud wall (China).
If asked to define a typical greenhouse, most growers in North America or Western Europe would describe a highly automated, multi-hectare greenhouse with state-of-the-art irrigation, and modern heating and ventilation systems. Vegetable crops would likely be cucumbers, tomatoes or peppers. The ornamental range of products is, of course, much larger, but the prominent crops that might come to mind are bedding plants, chrysanthemums, orchids and poinsettias.
In our travels, we do see plenty of greenhouse operations as described above, but for millions of farmers around the world, their reality is much different. The greenhouse structure itself could be constructed from whatever local raw materials are available. There may not be any electricity or heating capabilities. Irrigation water could come from a polluted lake and it might have to be applied by hand. The greenhouse crop could be orchids or tomatoes, but in some areas it is more likely to be bananas, eggplant, grapes or beans. There may not be a winter season to help reduce insect populations. Outside temperatures could be a constant 55°C during the day or humidity could run at 85 per cent each day with tropical rains. Yes, these are real situations for millions of greenhouse growers around the world and the growing conditions under which we are asked to give crop production recommendations.
|Straw mats help conserve heat (China).
|Mud wall construction without poly (China).
|Bamboo structure with wire and rags (China).
|Greenhouses going up the hillside, each operated by one family (China).
|Eggplant crop inside mud walled greenhouse (China).|
|Newly planted tomato crop (Brazil).
A typical greenhouse here could be several hectares and employ many people. Inside shade cloth, on an automatic track system, is a necessity to provide protection from the harsh sun. Dust from constantly blowing sand covers the poly quickly and provides an additional barrier. Inside the greenhouse there is a noticeable 10° drop in temperature. Curtains of water, running down mesh hanging from one greenhouse wall, act as an air conditioner and also add much needed humidity.
From this desert area of hot, dry extremes we move to another area of extremes – hot, humid and wet. In Brazil, it can also be challenging to get to some operations. After a couple of hours travelling along a deeply rutted, dirt or mud road (again with four-wheel drive) up ahead there is a greenhouse on a hillside. It is about one hectare and inside there are probably cucumbers, tomatoes or peppers growing.
On the way, the scenery is breathtaking… steamy jungles, towering waterfalls. While the scenery and the roads certainly make it an adventure, getting supplies in and produce out can significantly add to the cost of production. In the tropics, the need for the greenhouse structure is to protect the crop from the excessive daily rains that would otherwise leach nutrients away and potentially damage plants. Greenhouses are built on large raised beds to ensure that water runs away from the crop area. Ditches and canals around the greenhouses also help to divert water from the daily downpours.
As insect pests are a constant problem, many of the greenhouses will have fine-meshed screening covering the vents. With the reduced airflow caused by the screening and the already high levels of humidity, evapo-transpiration is low and plant growth can be sluggish. Many of the smaller operations rely on local building materials to keep the construction costs to a minimum. Bamboo-framed hoop houses with a poly cover are common.
China is another country where local building materials are often used, but the structures are different. Much of the construction is bamboo and wire with a poly cover, but greenhouses are often dug into the ground to help maintain more constant temperatures. Very few of these greenhouses are heated, so walls will be constructed of mud, which absorbs heat during the day and then releases it slowly throughout the cooler nights. Straw mats placed over the greenhouse plastic assist to conserve heat at night.
Ventilation in these structures is poor to non-existent and both temperatures and humidity will climb to excessive levels during the day. Imagine entering a greenhouse by pushing aside a straw door curtain. Inside the small dark entrance, there might be a cot or a cook stove and there could be boxes of just picked produce, such as melons or cucumbers. With barely enough room to manoeuvre, duck down and enter the main part of the greenhouse through a narrow, low opening. Then brace yourself for the impact of heat and humidity that makes it almost impossible for the un-acclimated to stay in the greenhouse for any length of time. And we thought that greenhouses in Ontario in August were uncomfortable! Not all greenhouses are of this construction. Some are much more modern in structure, but with few of the other technologies that we would consider standard.
In a country with a population of 1.3 billion, there are 750 million farmers in China and great expanses of greenhouses for the growing of food alone. In many areas, there could be as much as 50,000 hectares in one location and these greenhouses will fill the landscape like flood waters around the contours of the land. The land is all owned by the government. Until recently, farmers were only allowed one half-hectare of land. Consequently, greenhouses are small, structurally inexpensive and usually operated by one family.
Travelling to all of these different places and seeing the many greenhouse operations shows us the huge range of structures that exist in the world today. There is quite a contrast between the most basic greenhouses in China where everything is done by hand, and a huge operation in the Netherlands where everything is mechanized, with benches and plants whizzing by as they are automatically transported to their next phase of production. Regardless of the level of sophistication and technology, the basic purpose of the greenhouse remains the same… to provide protection to crops so that quality and yields can be maximized. We are constantly amazed by the resourcefulness of growers and the ingenuity required to manage their particular operations and we feel privileged to be a part of the process.
In upcoming articles we will be sharing more of our experiences with different crops, technologies, media, irrigation and fertilization practices. ■
Brad McDonald is sales manager with Plant Products Ltd., and Jennifer Wacasey is regional manager with the company’s International Division.