- Natural lighting of greenhouses – nuances
- Artificial lighting in greenhouses
- Greenhouse water supply
- Greenhouse ventilation – ventilation
- Heating of greenhouses
A greenhouse is similar to an incubator, with the difference that a greenhouse incubator for plants goes through a full cycle of their growth and maturation. Choosing an acceptable place in the country landscape, installing the greenhouse frame, overlapping it with a light-transmitting fence and correctly orienting to the cardinal points will not be enough. Technological equipment is required – water supply, heating, electric lighting, air exchange. Complete isolation of greenhouse plants from the external environment during the warm and cold seasons creates a number of questions, the answers to which will be given in this article..
Natural lighting of greenhouses – nuances
First of all – the orientation of the position from east to west, in which the sun’s rays will penetrate into the greenhouse from early morning until late evening. There should be as few shading trees and buildings as possible around the greenhouse, keep in mind that in the cold season the shadows from them will be two to three times longer, because the sun will be at a sharper angle to the horizon than in summer.
Of great importance is the light transmission of the greenhouse envelope – the worst option for covering in this sense will be polyethylene film, and well-transparent glass or polycarbonate must be washed from dirt at least twice a season.
The color of the inner elements of the greenhouse frame, frames and shelves should be only white. This measure will significantly improve illumination and, at the same time, reduce the thermal effect of sunlight on the structural elements of the greenhouse..
For better natural illumination at the beginning and end of the cold season, you will need reflective screens made of foil or galvanized iron, ordinary mirrors are also suitable – they can be used to direct the sun’s rays to those parts of the greenhouse that are least illuminated by natural light. Carefully monitor the development of plant crops so that some plants with their leaves do not cut off the light of others. A few important points:
- for crops with a predominance of the vertical position of the leaves, side illumination will be much more effective;
- with the vertical position of the light sources, the foliage of plants receives a different amount of light, decreasing in the direction from bottom to top, there should be several light sources, moreover, located at different angles;
- it should be borne in mind that diffused light is of great importance for plants.
Artificial lighting in greenhouses
At first glance, an increase in daylight hours encourages plants to grow actively, but – in plant cultures there is their own development program laid down by nature, under which the duration of lighting should be adjusted. The situation is as follows: the summer solstice, the highest position of the star above the horizon and the maximum duration of daylight hours, occurs annually at the end of June and is the main event in the plant kingdom. If up to this point the cultures are actively growing, then after the solstice, the fruit development program is launched, because plants need to take care of the continuation of their kind.
The task of the greenhouse owner is to correctly build artificial lighting, simulating the solstice for plants at the end of May, for which, throughout the spring, add 1–2 hours of artificial light to natural light every day, then gradually reduce the time of artificial lighting by switching only to natural lighting. In the last days of summer, when natural light is declining, daily daylight hours are reduced by 5 minutes, it is necessary to adjust artificial lighting for the summer solstice (late July – early August), daily increasing the period of additional lighting by 4 minutes. In building the right lighting, the owner has two options – to develop a schedule of daily backlighting in spring and late summer, controlling the period of artificial lighting independently and manually, or, more conveniently, entrust this task to an automatic controller by giving it a lighting program suitable for a given culture.
Greenhouse lighting requires a complete rejection of incandescent bulbs, which are very hot and have a short lifespan, not to mention high energy consumption. Fluorescent, fluorescent and LED bulbs are suitable and can be placed directly above the beds without fear of burning the plants. High pressure sodium lamps are often used in greenhouses, but they are heavy and very noisy..
According to research by scientists, the spectral range of sunlight has different effects on plants:
- the range from 280 to 320 nm is frankly harmful;
- the range from 320 to 400 nm is acceptable, but only in a few percent;
- blue, from 400 to 500 nm – useful for photosynthesis;
- green, from 500 to 600 nm – very useful because possesses high permeability, penetrates to the lowest tiers through dense crops;
- red, from 600 to 700 nm – is essential for photosynthesis and plant development;
- far red, from 700 to 750 nm – is necessary for the regulation of processes, a few percent in the general illumination is enough;
- range from 1200 to 1600 nm – increases biochemical reactions, is actively absorbed by water inside plants.
Certain crops require a specially aligned spectrum of artificial lighting, as they have different needs for its ranges. For example, the predominance of the red spectral range in artificial lighting can completely ruin the harvest of cucumbers and, conversely, greatly increase the harvest of tomatoes..
The choice of a scheme for organizing artificial lighting, the frequency of its use and the type of lamps used are extremely important, this should be treated with maximum attention and seriousness.
Greenhouse water supply
The importance of water for plant crops, especially those grown in isolation from the external environment, is obvious – all their vital processes are associated with the presence of available moisture, without which the wilting process begins. So why not introduce water without restriction, but no – an excess of moisture in the soil and air, which favorably affects the growth of shoots and completely eliminates wilting, leads to inadequate development of root systems, a delay in flowering and fruiting. On the other hand, with insufficient water supply, crops grow slowly, bloom and bear fruit earlier, but their yield decreases. By combining excess and scarcity of water, plant development can be controlled: frequent watering will accelerate the growth of stems and foliage; by reducing the water supply, increasing the ventilation of greenhouses, you can shorten the flowering and fruiting times of crops.
The moisture requirements among plant crops are not the same and are related to the size and number of foliage, biological characteristics, root system area, and growth duration. Most of the water supplied to the plants will be evaporated by them – the actual use of water in the growth and development of fruits does not exceed 0.3% of the total volume consumed by the plant. There are several ways to reduce the volatility of water: by increasing the potash and phosphorus feed; the introduction of organic fertilizers; reducing the amount of nitrogen fertilization; an increase in the humidity level in the greenhouse.
The greatest need for water in plants is during the germination of seeds, when planting seedlings. At the same time, low light and excessively moist soil will slow down crop growth. Especially on the level of soil moisture, seedlings and crops are dependent, actively developing stems and leaves with a poorly developed root system, like dill, radishes and lettuce. Irrigation should reach a depth of half a meter depth of the soil, surface irrigation will only dry up the topsoil. It is important to maintain the temperature of the water for irrigation not lower than the temperature of the greenhouse soil or the temperature inside the greenhouse in cases of hydroponic or aeroponic cultivation methods. Low temperature of water for irrigation will cause rotting of root systems, and at high temperature inside the greenhouse – shock state of plants.
The basic rule of irrigation is that water should not fall on the leaves and trunks of plants, should not contain any harmful impurities, such as salts of sodium, magnesium, boron, chlorine, calcium and heavy metals, fluorine and sulfates (a laboratory test is required). The content of organic acids of natural origin and phenol in water for irrigation is unacceptable. If the irrigation water contains a significant percentage of iron, then the stems and leaves of plants will receive multiple burns and will acquire a brown color. Contrary to popular belief about the suitability of rainwater for irrigation, it should not be used without preliminary purification – among the side effects of technological progress, contamination of the atmosphere with pesticides that manifest themselves as “acid rain” is extremely common.
Irrigation rates for crops depend on a number of conditions:
- watering is carried out less frequently in the cold season (including early spring) and on cloudy days;
- abundant watering is necessary in the warm season (starting in late spring), when the weather is clear and sunny, the air temperature is high with low humidity.
The highest irrigation rate in greenhouse farms used in the warm season is from 10 to 12 l / m2. In August, the volume of irrigation is reduced by a third, in December, watering will be half of the highest summer volume.
The deeper the root system of crops penetrates, the more water it needs. For example, a cucumber with a root system lying in the upper part of the soil needs 3-4 l / m2 water, and a tomato, whose root system develops more deeply, will require from 6 to 8 l / m2 water. The characteristics of the greenhouse soil are of great importance: with light soil, watering should be less abundant, but rather frequent; moisture-absorbing heavy soils require abundant, but rare watering.
Lack or excess of moisture in the soil is determined by the appearance of plant foliage and soil sample. The dark color of the foliage signals insufficient watering – their edges turn white, the leaves themselves often fold into an umbrella and become fragile. Excess moisture leads to active growth of the leaves, they acquire a pale green color. To assess the degree of soil moisture, you need to pick it up in your hand and squeeze it: at 40% moisture, the formed lump crumbles from a light touch; at 60% humidity, it will not collapse, but pressing will cause cracking; at 80% humidity the lump will retain its shape and strength.
Watering in the greenhouse is carried out in the following ways: surface, sprinkler, hole, drip and subsurface. With the hole method, one of the oldest in the greenhouse industry, a shallow recess is arranged around the trunk of the plant, into which water is poured. The disadvantage of this method is the high consumption of water, which is difficult to control; with a lack of moisture, it does not reach deep roots, which harms the plant. You can improve this method of watering as follows: take 1.5–2 l plastic bottles, cut off their bottom, screw the lid onto the neck, make several holes with a nail on different sides of the neck and dig in with the neck down at a short distance from the trunk of the plant so that the bottom of the bottles protruded slightly above the ground. By supplying plants with water through such funnels, you can bring moisture directly to the lower roots, completely covering their water needs.
Sprinkler irrigation, when water spreads to the beds from above through a spray nozzle installed on a garden hose or through a garden watering can, is unacceptable for most crops – water droplets on their trunks and leaves act as lenses, collecting sunlight and burning the plants. The only exceptions are those plants that need a particularly humid climate – when watering them with sprinkling, it is necessary to ensure that each plant receives enough moisture, because with large upper foliage, the leaves of the lower tiers will not get water.
The surface irrigation method, popular on open ground, is absolutely unacceptable in greenhouses – evaporation from a large area of the water mirror will cause high humidity, a limited irrigation area is difficult to control and water spillage is inevitable throughout the greenhouse.
Drip irrigation in greenhouses will be effective, facilitate the supply and reduce the consumption of water itself, the introduction of mineral fertilizers and minimize the participation of the greenhouse owner in the irrigation process. How to build a drip irrigation system, what its components are needed – see this article.
Irrigation using subsurface irrigation systems is more efficient than drip irrigation, but such systems are especially expensive. With this method of irrigation, water flows to the roots of plants through a system of pipes with holes dug to 0.25 m depth with an increasing slope from the water inlet to the end cap of each tube – the slope is necessary to displace air from the pipes. The advantages of the subsurface irrigation system in high-quality moistening of plant root systems, uniformity of irrigation, the lowest possible evaporation of water, invariability of the soil structure.
Greenhouse ventilation – ventilation
Excessive temperature rise in the microclimate of the greenhouse will be detrimental to plants – if the internal temperature exceeds 35 ° C and lasts for some time, the damage caused to crops can become irreversible. High humidity levels in greenhouses lead to mold growth and plant rot.
If the acquired standard greenhouse design has only one transom on the wall and a pair of transoms on the roof, then they will not be enough – at least two lateral transoms located on opposite walls are required, and on the roof, at least two (preferably four) vents are required, located along two roof slopes.
Ventilation of the greenhouse is carried out by opening the transom vents, the total area of which must be at least 15% of the entire area of the translucent fence. Openings-vents are arranged in the roof and side walls, in the case of a hard covering, the transom fencing should be fixed in the open position, if the fence is film – rolled into a tube and fixed, for convenience, rounded wooden strips should be fixed on the lower part of the film fence in places of its periodic opening.
The optimal solution to the issue of greenhouse ventilation will be swing vents on the roof slopes and blinds on wall transoms with manual or automatic switching of the “open” and “closed” positions. Ventilation shutters on the side walls are convenient for several reasons: their shutters do not interfere with interior work, because do not overlap spaces when opened; in the cold season, they will save heat, while providing a small flow of fresh air; with them, opening the vents on the roof will not cause sudden gusts of wind inside the greenhouse.
The automatic ventilation of greenhouses is especially convenient – equipping the transoms with a pneumatic or hydraulic piston. The principle of its operation is simple: when the temperature inside the greenhouse rises to a certain level, the pressure rises inside the piston and, moving forward, it opens the window. A drop in temperature causes a reverse reaction and the window closes on its own. It is required to adjust the piston stroke so that the transom opens to the required angle with subsequent tight closing.
It is advisable to install an electric exhaust fan above the entrance door, calculating its power over the greenhouse area – 1.2 m3/ min. for every m2 area. The water resistance of the electric fan must be at least IP 44, and its side facing outward must have shutters that automatically close when it is turned off. Remember that the humidity level in the greenhouse is quite high! It will be convenient if the electric fan is equipped with an adjustable temperature sensor that controls its activation and deactivation. However, it is possible to build a switch controlling its operation into one of the automatically opened transoms and then the fan will turn on and off simultaneously with the opening and closing of the transom vents.
The way of ventilation of the greenhouse through the front door suggests itself, but this opening does not fully fit, because too strong and harsh a gust of wind coming through it can damage greenhouse crops. If, nevertheless, the entrance door is used for ventilation, it is necessary to equip its sash with a reliable lock that prevents opening wide open under gusts of wind.
Heating of greenhouses
In the cold season, you can’t go anywhere from heating the greenhouse, unless you stop its operation. The main difficulty of this issue lies in the natural convection of air – warmer air will rise upward, quickly cool when in contact with the transparent enclosure of the greenhouse and descend to the ground already cold, i.e. heating the air is ineffective, because the soil needs to be heated, and it will only be cooled.
Therefore, it is better to equip winter greenhouses according to the shelving method of growing crops, abandoning the closed ground. Plant racks can be heated with electric, gas and infrared heaters.
The advantage of electricity is the convenience of its delivery and environmental friendliness, the disadvantage is its cost. For heating greenhouses, heat fans can be used, which are effective for quickly warming up the air, only they cannot be directed directly at the plants. It is convenient to heat racks and trays with seedlings with electric panels with heat radiation – their design contains heating elements covered on both sides with an aluminum film, a built-in thermostat maintains a certain temperature. In general, the presence of a thermostat and thermostat in any electrical appliance for heating greenhouses is very convenient, since the owner practically does not have to monitor their work.
Air heating of the inner perimeter of greenhouses with the help of gas is arranged as follows – the air is heated at the place of installation of a heating device operating on natural gas, then it is directed through the air ducts to the greenhouse. The convenience of this heating method is in the high efficiency of gas boilers, their full automation, there is no need to lay heating pipes. The disadvantage of the air heating method is the rapid drying of the air, the need for additional humidification.
Infrared radiators will be an exception among air heaters. They are powered by electricity and are relatively new heating devices in the world. There are several advantages of infrared heating: absolute environmental friendliness, high efficiency and, importantly, the absence of the effect of drying out the air. The principle of operation of these heaters is based on heating not the air mass, but objects in the radiation zone of the electrical appliance. Infrared emitters are silent and do not interfere with the work in the greenhouse, as they are placed on the ceiling. In terms of energy consumption, they are more economical than conventional electric heaters, although they are more expensive..
Ground greenhouses can be heated with water and electric heating; in both cases, the heat carriers go deep into the ground to a depth of 0.4 m.First, a sandy drainage layer 0.3 m thick is laid, then electric heating cables or heating pipes made of metal-plastic in increments of 0.3 m, a half-meter layer of soil mixture is poured on top. Water for pipeline heating systems is heated in a gas boiler, which is led out into the boiler room outside the greenhouse – it needs an exhaust system, which is not very convenient to build into a transparent fence. Warm water circulation is provided by a water pump.
One circuit for water heating systems will not be enough, moreover, each of the circuits requires a different water temperature. The temperature of the soil heating system should not exceed 40 ° C, otherwise the plant roots will dry out. And in heating tiers located at a distance from the ground, the temperature is set within 60-65 ° С.
Small dacha greenhouses can be heated by connecting to the heating circuit of the dacha itself, with sufficient power of the main heating boiler. Connecting to the main heating circuit through a plate heat exchanger, which simplifies regulation and insulates the heating circuits of the building and greenhouse, at a depth of 1.5 m, a heating main is laid from metal-plastic pipes laid in concrete channels with waterproofing filled with expanded clay for thermal insulation. But if the heating needs were not included in the parameters of the main heating boiler when designing a summer house, it is better to abandon the idea of connecting an additional circuit and install a separate heating boiler for the greenhouse.