A greenhouse, also called a hothouse or glasshouse, is a structure where vegetables, fruits, and flowering plants are cultivated under a controlled temperature. The roof and walls are made of either plastic or glass. It protects the crops from extreme weather conditions. It also helps keep away pests. Hydroponic gardening can also be done inside a greenhouse.
The ceiling and walls transmit sunlight, which is then converted into thermal or heat energy. The sunlight, after being absorbed by the plants, is reflected back. However, the sunlight can no longer pass out through the structure, because the reflected waves have longer infrared wavelengths. It continues to heat as more and more sunlight is trapped. As the plants start heating, they emit moisture, which in turn produces humidity inside the greenhouse. These conditions are extremely favorable for the overall growth of the plants. However, during winter, artificial heat has to be provided to maintain a stable temperature inside the greenhouse.
Before starting with the construction of a greenhouse, you should select the plants or vegetables that you want to cultivate. For instance, if you wish to cultivate exotic flowering plants, it should be constructed in a way that it meets the temperature and other conditions needed by those plants. Moreover, if you want to cultivate tropical plants throughout the year, you will need to build a permanent greenhouse. You can build it either as a freestanding building or you can attach it to your house or terrace.
Choosing the Site
You should select the site of the greenhouse in a way that it beautifully blends with your home and garden. The site should receive adequate sunlight, especially during the winter months. It should however, be sheltered from strong winds. A good water supply and drainage system near the greenhouse is absolutely necessary. For growing plants it is important to ensure that tall buildings and trees near the site do not block the sunlight.
Choosing the Style
You can design your greenhouse in a variety of styles. Lean-to ones, though smaller in size, can be attached to the wall of your house or garage. Classic A-frame styles have high ceilings and are slanted at the sides. They are inexpensive and easy to build. You can use polyethylene sheets if you plan to build your greenhouse in hoop style, also known as Quonset hut style. Gothic arc style, similar to hoop style, have straight wall and pointed roofs. You should style it depending on the temperature you wish to maintain inside the structure.
Building the Foundation
Before building the foundation, you should level the site and remove all the weeds and plants from the soil. You can either opt for wood or concrete foundation. For home greenhouses, wood foundation is an excellent choice. It is inexpensive, as well as easy to build. If it is attached to your house or garage, it is better to build a strong concrete foundation.
Building the Floors and Walkways
It is important that you plan a drainage system before building the floors and walkways. If your greenhouse is a permanent structure, you can build a concrete floor. But the floor should be sloped so that the excess water naturally flows to the drains. If you think that building a concrete floor is an unnecessary expense, you can leave the floor bare and instead construct concrete walkways. This will facilitate easy mobility of tools and equipment inside the greenhouse. Decorative tiles and colored stones make beautiful walkways.
Choosing the Working Area
You should select a work area where you can store your garden tools, potting soil, and fertilizers. It will be convenient if your work area is near the potting benches. You can also install a wash basin and a tool rack in that area. Storage area, if located outside the greenhouse, should be protected from rain.
Choosing the Covering Material
You can either use glass, fiberglass, or polyethylene film as the covering material for your greenhouse. A glass covering, though a bit expensive, gives a beautiful look to your greenhouse. It also helps in retaining the humidity. You can also use tempered glass, which lasts longer than regular glass. However, the foundation and the frame construction has to be strong, if you are planning to use a glass covering.
Fiberglass, when used as a covering for your greenhouse, can last up to 15 – 20 years. Less structural support is needed to install fiberglass covering because of its light-weight. Fiberglass coverings retains more heat than regular glass coverings.
Polyethylene film covering requires less structural support. Though it is cheaper than other covering materials, it can last for just 2 – 3 years. Double layered polyethylene film, when used, is more effective in retaining the heat than single layered film.
Polycarbonate glazing sheets, when used as a covering material, permits the maximum amount of light transmission inside the greenhouse. These sheets are light-weight and easy to install in personal greenhouses.
Choosing the Framing Material
You have to select the framing material based on the type of covering you have selected. If you are planning to use glass coverings, then aluminum or galvanized iron frames is the best choice. These frames are durable and require very less maintenance. You can also use treated lumber wood and PVC pipes as framing materials. The framing material should be strong enough to withstand harsh weather conditions. It should also provide the required structural support to the covering material.
Installing potting benches to keep your container plants will save you a lot of space. If you plan to use wooden bench, it should be painted with preservatives to prevent decay. Concrete benches are durable and can be installed, if you are planning to build a permanent greenhouse. Metal benches, though a bit expensive, last longer and they are resistant to rot and decay. However, before installing benches in your greenhouse, you should take certain factors into consideration. First, you should make sure if the bench is able to support your pots. Next, the benches should be installed in a place where there is adequate air circulation. A good drainage system near the bench area helps drain out the excess water from the pots.
Ventilating your greenhouse helps regulate the inside and outside air temperature. A good ventilation controls pest infection, and it also ensures that the plants get adequate fresh air for photosynthesis. For ventilating your greenhouse, you can either opt for natural flow-through ventilation or forced-air ventilation.
In natural ventilation, the cool outside air is drawn inside the greenhouse by the side vents. Whereas, the warm inside air rises and exits through the top vents. Natural ventilation, though inexpensive, is not very effective for cooling the greenhouse during summer. Controlled by a thermostat, a forced-air ventilation system has a fan that draws the cool air inside the greenhouse, with the help of a vent. The fan also helps in drawing the hot air out, through the vent opposite to the fan. For effective cross-ventilation, there should be several vents near the base and one or two large vents near the roof of the greenhouse.
Before heating the greenhouse, you should check if the covering and frames are insulated. If the structure is attached to your house or garage, you can use your home heating system. Gas heaters are also effective for heating the greenhouse. You can use polyethylene vent tubes to distribute the heat throughout the building. These vent tubes, when fixed near the potting benches, facilitate increased plant growth.
If you live in a region where you get adequate sunlight throughout the year, you can use solar power to heat the place. The covering material should be such that it transmits the maximum amount of solar energy into the greenhouse, without any significant loss. You can place water filled containers, rocks and concrete directly under the sunlight in order to store the solar energy. Solar greenhouses not only collects the solar energy during the day but also store it for heating the greenhouse at night, as well as in cloudy days.
You can use Venetian blinds or wooden screens to cool the greenhouse during summer. However, the degree of cooling required will depend on the light requirements of the plants, as well as the heat retaining capacity of the greenhouse. You can also try some evaporative cooling techniques. Pad and fan system works well in cooling and humidifying air inside. These systems have a wet porous pad that draws the outside air, and evaporates the water that is inside. Unit coolers are very effective for cooling home greenhouses. A metal box and evaporative pads are fixed on the outside wall and the three inner walls respectively. The cooler draws the outside air through the pads and the ducts bring in the cooled air. You can also spray a latex paint on the covering of the greenhouse. These paints, diluted in water, help in cooling the greenhouse, and can be applied before the onset of the summer.
Building a home greenhouse is a very rewarding and fulfilling experience. Moreover, nothing can match the happiness and exhilaration that you will derive when you watch the flowers bloom right in front of your eyes.