The purpose of a greenhouse is to control the growing environment. Plants require a limited range of temperature, soil moisture, light, humidity, air (Oxygen, Carbon Dioxide and Nitrogen), and nutrients to grow. Plants also require some type of physical support for roots and shoots. Plants also depend upon symbiotic relationships with fungi and insects to grow and reproduce. The greenhouse covering helps control many of these factors to help increase plant growth and reproduction. But exactly, what factors are being controlled in the greenhouse?
A Greenhouse Can Control:
- Heat – Attempt to prevent freezing or overheating – for tomatoes and other warm weather vegetables, some horticulturalists assume no growth occurs below 50°F (10°C) or above 86°F (30°C), blossoms may drop off if temperature is above 85°F (29°C)
- Water – No direct rainfall on soil inside the greenhouse, so irrigation must be provided, water volume and timing can be controlled to optimize growth
- Light – Any covering will block some percentage of light (or particular wavelengths of light) available to plants – shading may be beneficial when too hot
- Air Flow and Humidity – If the greenhouse is totally enclosed, humidity will increase, and since healthy, growing plants are “Net Carbon Fixers”, Carbon Dioxide will decrease and Oxygen will increase. (The reverse is true at night when plants use more Oxygen and release Carbon Dioxide as they “digest” the food they made from photosynthesis. But since growth occurs, the net result is decreased Carbon Dioxide). Nitrogen will also decrease for Nitrogen-fixing plants, so decreased air flow may be detrimental to plant growth. Blossoms may drop off some plants at extreme low or high humidity
- Pests– The greenhouse may lock out some potential pests, but may also lock them in and the greenhouse may actually provide an excellent habitat for plant pests that is safe from their natural predators
- Pollination – Insect pollinated plants will need bees for pollination, wind pollinated plants need wind, even self pollinated plants benefit from being physically jostled by wind or insects or from sonication (vibration) by bees.
Most of us begin the quest for a greenhouse for the purpose of controlling heat (or lack of heat) for certain plants. We may only want to control the heat, but we are also controlling the water, light, air flow, pest and pollination all at the same time. Fact is we may be trying to protect our plants from frost, but if we don’t pay attention, we may also let plants over-heat in the greenhouse. So, we either pay very close attention and adjust everything by hand, or we depend on technology (automatically controlled systems) to control the greenhouse environment.
Types of Automated Systems to Help Control the Environment in the Greenhouse
- Irrigation – Can water on regular schedule or when soil falls below preset moisture level
- Ventilation – Thermostat can automatically turn fans on and off or open or close louvers
- Shading – Thermostatically controlled shade cloth automatically shades plants
- Cooling – Thermostatically controlled air conditioning system
- Heating – Thermostatically controlled heating system – usually propane or natural gas
- Misting – Automatic misting to raise humidity, or in conjunction with fans to aid cooling by evaporation
- Nutrient Dosing – Nutrients can be automatically dispensed with the irrigation system – complex systems include computer soil analysis
- Auto Pest Control – Programmable systems that automatically spray pyrethrins much like deodorizers in public restrooms
- Dual Layers and Inflation System – A very good insulation system – includes a double layer of plastic film supported by air pressure from fans
How much and which types of automated technology we incorporate into the Greenhouse will largely be a function of cost. Low tech or no (zero) tech is least expensive, but it also means that you have to do all the work. If it gets too hot, you have to go open or close the greenhouse, and you also have to remember to close it back up in the evening before all the heat is lost. If you don’t, your plants and the harvest will suffer. Now take a look at types of greenhouse designs.