As optimal as a sun-drenched greenhouse is for seedlings and young plants during the frosty winter and spring months, the dry and hot summer time with its extreme temperatures can have an even more problematic effect on the plants housed under the roof. Tropical heat is difficult for the plants, so that some technical precautions are necessary in the greenhouse even at temperatures above 30° C. Why is that?
Why is shading important in the greenhouse?
Greenhouse shading is necessary to protect plants from overheating and damage caused by intense sunlight. Options for this include chalk paint, shade nets, reed mats or internal roller blinds to regulate temperature.
When too much sun is harmful
The optimal comfortable and growth temperatures for greenhouse plants are between 20 and 30° C, depending on the genus or species. If windows and doors are closed, extreme values of over 50° C are reached relatively quickly in summer, which in turn leads to this that the plants' vital protein compounds and enzymes gradually decompose. In addition, there is the so-called glass house effect, which from a physical point of view ensures that short-wave sunlight in the interior is converted into long-wave heat radiation and is also reflected multiple times by the glass surfaces.
What happens to the plant when it is hot?
Under normal temperature conditions, plants use evaporative cooling, which occurs automatically on their surface. The higher and faster the internal temperature in the glass house or foil tent rises, the more water has to be broken down inside the plant in order to keep the “normal temperature” constant. However, this form of conversion has its physical limits, so that in the medium term, significant leaf changes (sometimes even visible damage) must be expected in the range between 30 and 33° C. It usually only takes a few days before the first long, weak shoots become visible, which can even die shortly afterwards.
What is a climate-friendly greenhouse?
The best and most important thing you can do to your plants in the greenhouse is a good climate. Some of the prerequisites for this can be created by purchasing a greenhouse that is equipped with as many ventilation openings as possible. In cheap models made of clear glass, where savings have been made on windows and doors, there is usually a risk of rapid sunburn. It is equally important that these openings are at different heights, because for a he althy climate there must also be well-functioning and flowing air circulation, which should otherwise be retrofitted with an additional fan.
From chalk and shade nets to reeds and cooling interior blinds
It is well known that many roads lead to Rome and garden enthusiasts have at least as many options for retrofitting their greenhouse to be plant-friendly and optimal for the climate. A particularly inexpensive, quick and alternative shading that requires little effort is to paint the entire outer shell with a water and chalk mixture. And it goes like this:
Mud chalk & water – the (almost) free greenhouse shading
By far the easiest and most cost-effective way to retrofit your greenhouse with outdoor shading is to paint, roll or spray with chalk, for which you will need to obtain the following materials for a medium-sized house:
- 25 kg mud chalk
- 30 liters of water
- Brush, paint roller, painter's puff, paint bucket and stirrer
Before applying the liquid that is not too thick, the outside of the glass panes should definitely be cleaned at least roughly. Whether all sides need to be painted essentially depends on where the afternoon sun is most intense and creates a tropical climate inside the house. Nature will later take care of washing off the paint almost independently, because with every rain shower the paint will have almost completely dissolved by autumn.
Tip
If necessary, remove any remaining residue from the glass surface with a special or household cleaner before the start of the next growing season. It is better not to use this method for houses covered with plastic (double-wall panels), as this material is very sensitive to scratch marks, which are almost inevitable when the paint is subsequently removed.
Shade nets: high effect when used for several years
Shade fabric is available by the meter in all possible sizes and thicknesses from relevant garden retailers and will help you reduce sunlight by 50 to 60 percent. With an average weight of 60 to 100 g/m2, this dark green to black colored material is stabilized against UV rays, opaque, growth-promoting and even hail-resistant to a certain extent. The most common standard widths of the nets are:
- 1, 00 m
- 1, 50 m
- 2, 00 m
- 3, 00 m and
- 6, 00 m
The average prices at the time of writing of this article are between 1.45 and 1.90 euros per square meter with a material thickness of 60 g/m2. Due to the high resistance to temperature and rotting of the fabric, a service life of up to five years is not unusual.
Tip
It is essential to ensure that the shade nets are firmly seated, which find the necessary hold in the ground or on the greenhouse walls using special clips (with integrated eyelets), ground anchors or pegs or with a suitable net adhesive tape.
Shade maker made of reeds – natural and environmentally friendly
Natural reed mats are just as effective as the shade nets, which are usually made from synthetic materials, as long-term sun protection for greenhouses of all sizes. When installing the membranes, make sure that all existing windows and doors in your greenhouse can still be opened easily and completely afterwards to ensure unhindered air circulation. Unless you come across particularly inexpensive reed mats in special offers outside of the gardening season, you have to expect prices between a good 3.00 to just over 5.00 euros per square meter when buying from most common online retailers.
Interior shading with roller blinds – a touch of luxury
The above-mentioned shade nets and reed mats are of course just as perfect for installation inside as on the outside of greenhouses. The roller blinds are considerably more comfortable when it comes to individual temperature control. Depending on the current intensity of the sunlight, the completely pre-assembled sets can be infinitely adjusted, which ideally leads to relatively constant temperature conditions throughout the interior of your greenhouse.
Of course, this luxury has its price: We discovered a 620 mm wide shading roller blind in a length of 195 cm with all mounting accessories in black and a shade value of 55 percent online for 129.00 euros plus shipping. For perfectionists, there are roller blinds and awnings as interior shades with motor drives, which are automatically controlled via several temperature sensors and, integrated into modern SmartHome systems, can be controlled even when you are away from the property.
