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How does a greenhouse work?
When the leaves start falling from the trees outside and the temperatures drop to the single digit range, it’s a sign that the end of the gardening season is near. Flowers are no longer blooming, vegetables have been harvested, and plants have been re-potted in frost-proof containers. Everything now has to wait until next year. True. Unless you’re a greenhouse owner. Here special rules apply for the climate.
A greenhouse consists of a translucent material such as glass, plexiglass or foil. The sun’s rays enter the interior of the construction and heat up the air and the heated air is unable to escape. This means that the temperature inside is usually warmer than outside. This effect enhances the growth of plants. A second major advantage of a greenhouse is its resistance to external influences such as wind and rain.
How to plan a greenhouse
Regardless of whether you want to build a greenhouse yourself or purchase a ready-made model, there are a few important factors to consider when planning your greenhouse.
Choosing the optimal location
In the back left-hand corner of the garden or over on the other side under a tree? You shouldn’t leave the location to chance. We give you a few useful tips below:
- Accessibility: the greenhouse should be freely accessible from all sides. This makes it easy to clean and repair.
- Light: position the greenhouse facing south to get as much sunlight as possible.
- Supply: proximity to the house is practical to save having to cover long distances unnecessarily.
- Location: make sure that the greenhouse is as free standing as possible – large trees nearby will reduce sunlight, while falling branches can cause damage. Positions on a slope should also be avoided, as water running down it could enter the greenhouse.
Size and material
The size of your greenhouse depends mainly on how you want to use it and how many plants you want to house. The smaller it is, the more difficult it will be to plant flowerbeds. The larger it is, the higher the acquisition and running costs. If you plan to place potted plants inside, the ceiling must be high enough.
You might think that all greenhouses are made of glass. Nowadays, however, there are better alternatives as a material for the walls and roof. Glass poses a safety risk due to the danger of breakage. In addition, excess heat accumulation, which is harmful to the plants, is more frequent in glass greenhouses.
The best solution is plastic. It is very hard wearing and lets most of the light through, but not UV rays. The heat transfer coefficient is low, which means that the heat loss per square meter is minimal, and therefore the insulation capacity is particularly high. You can obtain plastic sheets made of Makrolon, for example. Plexiglas, which has similar physical properties, is also a good option.
The frame of a greenhouse is usually made of metal such as steel or aluminum. It is very resistant to weather and pests.
Ventilation, heating and watering
For plants to thrive in a greenhouse, it is very important that they are supplied with everything they need. If there is sufficient water, an optimal temperature and enough fresh air, flowers, herbs and vegetables will all grow perfectly. We explain below how you can create the right atmosphere.
- Ventilation: temperatures in greenhouses can reach extreme levels. In summer, the interior can heat up to more than 50°C in some places. Proper ventilation allows heat to escape. Ideally, the temperature should be between 22°C and 24°C, and humidity between 60 and 80 percent, all year round. Air the greenhouse by opening the doors and windows once a day to achieve this.
- Heating: at night, especially in winter, temperatures in unheated greenhouses are around freezing point. If you choose to use the greenhouse only as a cold house, i.e. as a place for potted plants to hibernate, it isn’t necessary to install a heating system. However, if you want flowers to bloom and vegetables to thrive, you must keep the inside warm. You can ensure this by connecting the greenhouse to the central heating of your home or by heating it separately with a gas, wood or electric stove, for instance.
- Watering: how much you need to water the plants depends on what you are growing. Vegetables like tomatoes, cucumbers and peppers require a lot of water; lamb’s lettuce, radishes and many herbs are more easily satisfied. It’s not essential to install an automatic watering system. Simply watering the plants by hand with a watering can or hose is sufficient.
Building your own greenhouse
You may decide to build a greenhouse for your garden yourself – provided you have a bit of manual skill. The advantages are that you can customize it to your needs, and it will only cost a few hundred francs. Below we list the steps required to build a simple foil greenhouse made of wood.
- Lay the foundation: it’s vital to lay a foundation in order to ensure a high degree of stability. You need to be sure that the greenhouse will remain in the intended location for a while. As well as providing basic stability, the foundation also acts as insulation against the ground – heat loss is reduced. For large greenhouses you should cast a concrete foundation, for small models a construction made of square timber is sufficient.
- Create the basic framework: saw the beams for the base frame with a circular saw or a hand saw. Then fix the pieces into place with waterproof wood glue and fasten them with screws. Start with the side panels, then move on to the gable sides. Leave a space for the door at the front. Last but not least, add the beams for the roof.
- Cut the cladding to size: the simplest solution for cladding a greenhouse is to use foil, which is available in DIY stores by the meter. Cut it roughly to size, lay it over the base frame, fix it with a stapler, then remove any remnants with a carpet knife. Make sure that the foil is tight enough for rays of sun to pass through unhindered.
Buying a kit
The simplest solution is to purchase a kit. Thanks to detailed instructions, the greenhouse will usually only take a couple of hours to put together. We present two different examples below.
- Simple and affordable: this greenhouse from Hornbach consists of an aluminum frame and walls made of polycarbonate. One window and a space-saving sliding door allow air to circulate. The price of the greenhouse, which measures 195 x 195 centimeters, is quite low at 399 francs (price on 4 January 2021).
- Stable and bright: the main advantage of the ACD Greenhouse from gewaechshaus-shop.ch is the special garden float glass. This type of glass is seven times stronger than normal glass. Consequently, it offers maximum safety and has a long service life. The safety glass on the roof reduces the burning glass effect, protecting the plants inside. It costs 3,590 francs (price on 4 January 2021).
Tips for growing plants
In a greenhouse, you can basically grow and harvest all year round – regardless of the external conditions. Conversely, this will also give you plenty of gardening work to keep you busy all year long. So be sure you have the time and motivation.
Growing vegetables and herbs
Since the temperatures are mild on average, most vegetables and many herbs produce a rich harvest in a greenhouse. Vegetables such as spinach, radishes and tomatoes are popular, as they can be planted as early as March – as is the case in a cold frame. Basil, parsley, marjoram, oregano and dill are classic greenhouse herb varieties.
Flowers are intended less for the stomach and more for the eye. Blossoming potted plants such as the stylish calla or permanently flowering oleander feel at home in greenhouse conditions, for example. With sufficient heating, it’s possible to sow exotic climbing plants such as the sweet mock orange or passion flower. Even tropical fruits such as lemons, oranges and limes can be grown successfully with the appropriate care.
Conclusion: a covered all-year garden
Even if it’s raining outside or the first frost is setting in, you can still pursue your passion for gardening in a greenhouse. Thanks to the special climatic conditions, useful and ornamental plants can be grown virtually all year round.