Hobby greenhouses are used for ANY type of plant cultivation. Many people use them for specialist varieties of plants, such as Orchids, Clivias etc; They are used in research eg by universities etc and by the general public to keep plants warm in winter; and to grow seedlings for both flowering plants and vegetables through spring and autumn. In some cold regions of the world, due to a very short growing season, the only way to have a vegetable garden is to grow one in a greenhouse.
In winter, temperatures at night in the greenhouse should not go much lower than 7'C, depending on your plants. The trick is how to maintain the right temperature for your greenhouse during both winter and summer. In the summer months, the greenhouse must be kept cool - under 29'C degrees - if you want your plants to survive. Greenhouses can overheat easily especially in hot climates like we experience in South Africa. There are a number of ways to maintain the right temperature for your plants. Below are some tips and accessories that we strongly recommend to assure that your plants will be comfortable no matter how extreme temperatures are in winter and summer.
Choosing a Site for your Greenhouse
Choose a level, clean site, in a low traffic area with easy access. Consider the following factors:
• The change in the angle of the sun between summer and winter.
• Shade cast by the trees – in hot SA climates shading will help reduce temp.
• Growing trees and existing deciduous / evergreen trees.
Temperature/Light
The more sun that is provided, the more heat the greenhouse will produce. The more heat produced, the more ventilation is required. Place a thermometer near the middle of your greenhouse and monitor the temperature at different times. In hot climates, a simple option is to open the door/s in the morning and leave them open until late afternoon. Clients have reported excellent results in reducing the temperature in the greenhouse by painting the roof panels white. Recommendations: Paint product called 'Super-cooler U-12' (an Israeli product) available from Vegtech 2000 Pty Ltd. Another client recommends normal white PVA to be painted on the outside of the roof panels.
Greenhouse Shading
The shadecloth is probably the most important accessory you will need for your greenhouse, in particular, if you live in a very hot climate. The shading will shield it and your plants from excess sun between 10am and 5 pm or even until 7 pm, if your greenhouse has extreme western exposure. The RION shadecloth is of the highest quality and is used for any number of different types of plants. The cloth prevents irradiation damage to your plants, reduces the heat in the greenhouse in summer and adds insulation during the cold weather. Whatever type of shadecloth you choose, make sure the cloth is big enough to allow your vents to open as proper ventilation is another important key to maintaining the correct temperature for your plants.
Greenhouse Ventilation
Be sure to provide adequate window vents in your greenhouse. Cross ventilation will help prevent the greenhouse from overheating. Place the vents so that they will take advantage of prevailing winds. Most greenhouses should have vents that equal in size to 15% of the floor space. The roof vent should open 45 degrees above the top of the greenhouse. To make sure that your RION vents do not blow away, attach a wire or heavy-duty string to both sides of each vent and the greenhouse frame. Allow enough play in the wire or string to allow the vent to open and close as needed. In strong winds, be sure to close your vents and latch them securely.
RION offers two vent options, either a manual vent or an automatic opener accessory. We recommend the automatic opener which can be attached to all vents. The opener will automatically open and close the vents based on the temperature inside the greenhouse.
Louver windows are also options to increase cross ventilation, either the small louver for the back panel or the large louvers to fit the large side panels.
An alternative to extra vents is having a thermostatically controlled exhaust fan system. Using very little electricity, the adjustable thermostat automatically provides ventilation for your greenhouse. The proper size fan will change the air intake in about 2 minutes. To select the size for your greenhouse, determine the volume of the unit (Length x Width x Average Height) and multiply by 0.75 to obtain the ventilation rate in Cubic Meter per Minute (CFM). For the exhaust fan to operate effectively, fresh air intake shutters must be provided at the opposite end of the greenhouse. The shutters open with the flow of air drawn into the greenhouse by the fan or they can be opened and closed by a motor.
Greenhouse Misting / Humidity Control
Although shading and ventilation will keep your greenhouse from seriously overheating, the actual cooling of a greenhouse comes from the evaporation or moisture inside the greenhouse. The evaporating water soaks up heat like a sponge, when heat is used to change water from a liquid to a gas. Good air circulation from fans increases evaporation.
A good misting system disperses water evenly around the greenhouse. The amount of moisture needed depends on the amount of ventilation, shading provided, your climate and the weather. The most accurate and most reliable is an automatic system of misting nozzles. One common system is to soak the floor with a sprinkler hose, open your roof vents, and the entire unit will cool down quickly. This must be done a number of times during the hottest times of the day.
Only apply misting during the day to avoid excess humidity at night. Use a 24-hour timer to shut off the system 2 hours before the sun goes down. If you live in a dry climate, in addition to your misting system an evaporative cooler works well. Air is cooled 3 to 5°C degrees by water evaporation as it is drawn through the cooler and into the greenhouse.
More information on humidification is available on the Mist & Cool web site www.mistcool.com. Local Distributor in Pretoria is Francois on cell 082 484 9848.
Irrigation
Many owners choose the control of hand watering, however drip irrigation systems are effective and also prevent the leaves from getting too much water on them. Drip systems are gentle on seedlings, too. Over-watering in a climate controlled greenhouse environment has been the death of many a plant or seedling.
Heating
Greenhouses can be heated with gas, paraffin or electricity, with or without thermostat controls. Your heating requirements will depend on your plants, climate, location of your site, and the construction of your greenhouse. Your RION greenhouse with its UV coated Polycarbonate glazing is better than most greenhouses in providing sun protection, light diffusion, and heat insulation.
A heating system must be able to maintain the desired temperature during the day and night. Your inside temperature should not go below 7°C at night. For some plants even 7°C is too low. For larger greenhouses, gas heaters are recommended because it is less expensive. However, if your area suffers power outages, a gas heater might be more reliable. Any type of heating system you use should be properly vented to the outside of the greenhouse to avoid build up of any harmful gases.
To calculate how many BTUs your heater will need to provide and maintain the correct temperature for your greenhouse you will need to know:
- The area of your structure:- the total square meters of the surface area
(do not include the floor space).
RION: GH44 – 27m2 GH46 - 35m2 GH48 - 44m2
- Minimum outside temperature i.e. the lowest temperature for your area.
- Maximum Inside Temperature i.e. the highest temperature you would need inside the greenhouse.
- Heat loss value: For a RION greenhouse it is .70
Now the formula:
Take your Area and multiply it times the (Max temp. minus the Minimum temp). Multiply heat loss equals the minimum amount of BTU output your heater you will need for your size greenhouse.
Maintenance
Your greenhouse will have maintenance requirements. Look out for bugs and fungus and keep the greenhouse clean. Use herbs as natural insecticides. Look for natural / organic pesticides. Both the inside and outside of the Rion greenhouses can be sprayed down with the hose on jet nozzle. |
