Gardening Tips

Greenhouse, all you should be Know!

Greenhouse, all you should be Know!

Greenhouse, all you should be Know!

Different types of greenhouses

So you want to pamper your plants and put them in a greenhouse.  But how do you choose the right one? Which material will best look after your little darlings?  We will try to help you make the best choice.

You must first decide the type of greenhouse best suited to your needs :

  • The cold greenhouse whose temperature can go down to 4°C, suitable for plants with tough, non-porous skin.
  • The moderate greenhouse,  suitable for subtropical species which tolerate the cold.
  • The hot or tropical greenhouse, where the temperature is between 18°C and 26°C, which allows you to grow many tropical species and other rare plants.


Once you have decided on the type you want, now think of the choice of materials.  Four materials for the structure are available: wood, PVC, aluminum and steel.

  • This is the most aesthetic and offers the best insulation.  Choose rotproof wood without knots or cracks.  Good quality wood will last the longest – avoid softwood, which will quickly deteriorate if not treated regularly.  Make sure to insulate the floor of a wooden structure by using bricks – this will prevent the base of the structure from rotting.
  • PVC is the cheapest material used.  It offers good insulation, which limits condensation and saves energy.  It also doesn’t require much maintenance.  However, it degrades over time.  It doesn’t last as long as wood or aluminum and can’t support much weight.  It is therefore not suitable for large surfaces.
  • Aluminum is the most widely used material.  It is very resistant, especially to strong winds.  It doesn’t need much maintenance, it is light and doesn’t rust.  Good quality aluminum greenhouses can last up to a hundred years.  However, it doesn’t offer a good insulation.  To insulate it you should use a system of steel clip fasteners at each angle, along with PVC draft excluders or putty to insulate the joints.
  • For very big greenhouses, steel is ideally suited.  It is flexible and resistant but is rarely used for private greenhouses and should be galvanized to avoid rusting.
  • Alveolar polycarbonate is lighter an gives more insulation.  It also resists hailstones better.  However, it isn’t very resistant to strong winds and it must be changed after ten years as it tends to become opaque.

Heating the greenhouse

Greenhouse, all you should be Know!

Heating is necessary for your greenhouse in winter if you wish to keep it frost free, except of course if you live in certain southern regions.  If you have a tropical greenhouse, heating will be useful for most of the year, as this type of greenhouse requires an average temperature of 20°C.

Choose your heating system according to the surface of the greenhouse – you don’t heat the 10m² greenhouse in the same way as one measuring 100m².

Electric heating

Electric radiators are the best suited to small surfaces.  However, make sure to use special greenhouse heaters, as these are waterproofed and therefore correspond to this type of usage.

These radiators use hot air for heating, but ones which radiate heat using infrared lamps also exist and can be hung from the roof of the greenhouse.  This type of heater is used for surfaces of less then 6m² and a portable model also exists.

Tubular radiators can be installed along the sides of the greenhouse, but these are bulky and not easy to install.

For bigger surfaces, a hot air generator can be useful.  The level of air blown out can be adjusted by an atmospheric thermostat and certain models are remotely controlled.  These are the top-of-the-range models of electric heating.

Petrol heating

Used both as a backup heater for small surfaces and for cold greenhouses, this type of heater is easy to install, transportable and economical.  Be careful, however, to use sulfur-free petrol, as the presence of sulfur may be toxic for certain plants.

As this type of heater doesn’t have a thermostat, it needs to be closely monitored.  Make sure to fill it regularly, though some models can run for 7 days without being refilled.

Town gas isn’t used for heating as it is expensive and difficult to install.  Gas heating is thus carried out by Propane gas in bottles.  Butane is not suitable as it is too sensitive to frost.  Recent models are very safe and are leak-proof.

Gas heaters are 30% more economical than petrol heaters and some models are equipped with a very useful thermostat, which can be adjusted according to your needs.  Gas heaters also offer more autonomy than petrol heaters.

Placing your greenhouse

So you’ve decided at last! That greenhouse that you’ve wished for so long so that you could pamper your plants and prepare your spring sowing, is finally to be installed in the garden.  But be careful, it is essential to install it in the right place, so certain parameters must be considered if you wish to optimize its use and keep it in good condition for as long as possible.

Choosing the right place

Choose a sheltered place in the garden with plenty of exposure to the winter sun.  Avoid places where the cold accumulates in winter and humid places which will damage greenhouses with wooden structures.  A humid place also encourages the growth of mosses and other similar nuisances – these require constant treatment to remove them.

Place the side of the greenhouse, usually the longest side, facing south.  It will thus have the best exposition to the sun, which is important in winter when the days are short.

Avoid windy places

The wind is another factor not to be neglected when installing the greenhouse.  In some regions, strong winds can break the windows and even remove the openings.  To avoid this, install the greenhouse perpendicular to the dominant winds, placing the door at the opposite end to these winds.  Windbreakers can be installed for further security.  Otherwise, you can place the greenhouse behind a bamboo hedge or behind some shrubs.

These wind-breakers should be placed at a distance four times the length of the height of the greenhouse,  providing you have space.  Artificial wind-breakers may also be installed -these can be placed immediately.  Plastic models, of varying thicknesses, are available.  They are an interesting option as they are simple and quick to install and are good value for money. Remember that a greenhouse exposed to wind loses a lot of heat in winter, which means that you have to heat it more, and this costs money!

Don’t place it near trees

The greenhouse should be placed in a clearing far from trees, as these will create too much shadow.  If these trees are deciduous, or worse, resinous, this will create a lot of work for you – the windows will need to be cleaned very often.  What a pity – your time would be better spent looking after your plants than cleaning the windows of your greenhouse!

The wind may also cause branches to fall which will break the windows, and the roots of the trees may cause problems by lifting the structure of the greenhouse.  This is why you shouldn’t place it near trees.

So follow the above advice and your greenhouse will be placed in good conditions and will give you long hours of pleasure for a long time.

Ventilating the greenhouse

Greenhouse, all you should be Know!

The temperature and the rate of humidity of a greenhouse depend on its ventilation.  This complex process involves the exchange of heat between the inside and the outside of the greenhouse.  Controlling this is essential if your greenhouse is to function properly, as ventilation determines the temperature, the humidity rate and the concentrations of gas like CO² in the greenhouse.

The health of your plants depends on a good ventilation (breathing, photosynthesis, transpiration). Ventilation also provides good sanitary conditions for them.

Two types of ventilation exist : natural or artificial ventilation.

Natural ventilation

This is the most economical system for regulating the microclimate in the greenhouse.  It consists of openings built into the structure of the greenhouse.  These openings should represent 20% of the ground surface and have an opening angle big enough to let the air circulate properly.  It is recommended to have openings in the roof facing north, as these will allow the air to mix correctly in the greenhouse.

Openings on the sides at the level of the plants are also important, as these increase the efficiency of the roof openings and help modulate the ventilation.  This gives the best ventilation, creating a self-regulating internal circuit of air: the cool air sucked in by the side openings is heated up in the interior of the greenhouse, before rising and exiting through the roof openings.

In spring and in summer, you can obviously open the doors as well, thus bringing down the temperature inside the greenhouse.

Artificial ventilation

This type requires a specific electrical installation in the greenhouse: electric boxes with protected circuits, starters, lines, electrical channels, etc.. Having installed these, you can then set up your ventilator.  The most common types are helicoidal ventilators with shutters, which work like air extractors.

These extractors change the air inside the greenhouse and remove the CO²,  thus rebalancing the general climate inside.

Their outflow can be programmed, most ventilators having three or four levels of ventilation.  They should be installed at the end opposite to the dominant winds.

This type of installation may be used as a back-up to the natural ventilation of the greenhouse.  It is useful for ventilating places which contain plants with specific needs, guaranteeing ventilation at particular moments when conditions aren’t suited to their development (when heavy snow or strong winds prevent the openings being opened, for example).


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