Screen selection and chalking

In the cultivation of anthurium and phalaenopsis, often one to three screens are used. The number of screens depends on the location of the nursery and the type of greenhouse.

One screen
When you opt for one screen, the following considerations are important:

In countries with winters with sufficient day length and temperatures that do not go below 0 degrees, the combination of sun shading and energy saving is beneficial. A disadvantage is that you always have to leave a gap on beautiful days in order to prevent the temperature in the greenhouse from increasing too much!

At a lower outside temperature and with less solar radiation, the energy screen is a better option because it filters out relatively little light and during the day it can be kept closed for longer.

Chalking for sun shading is in both cases a good option in the warm summer months.

Two screens
In the event of using two screens, it is usually a combination of an energy screen and a shading screen. The shading screen can be manufactured in closed strips and open strips.

The advantage of the open strips is that the screen can be completely closed during sunny weather, which facilitates a beautiful, even climate under the screen. The main disadvantage is that the energy saving of this screen is much lower compared to a screen with closed strips. The shading screen can also vary in shading percentage. The lower the shading percentage, the more chalk has to be used.

The screen with closed strips has an advantage in the winter period. You can achieve the same temperature with a lower tube, as a result of which the plant maintains a better microclimate during cold nights (<0°C outside). For growers who want to cultivate faster in the spring, a closed screen can be beneficial. The temperature can be maintained without heating too much. A disadvantage is, of course, the summer climate. Due to the closed structure, the screen should always be kept slightly open, because little or no heat is evacuated throughout the screen. This can cause the temperature to increase considerably. With a closed screen you need more chalk, which can lead to higher energy consumption in a moderate spring/summer!

You can also opt for a diffuse shading screen. In terms of sun shading it is comparable with the Tempa and Solaro screens. The advantage is that this screen makes the light more diffuse, as a result of which the light penetrates the crop better. This ensures that the temperature difference between the upper and lower leaf is smaller, as a result of which the plant can grow better. In the end, this will lead to a higher growth rate, but it is still unclear how much exactly. A disadvantage of this diffuse shading is that its saves significantly less energy than shading screens with closed strips!

For regions with a moderate winter and warm summer, an energy screen with an open shading screen is the best option. In countries with a cold winter and moderate/warm summer, a shading screen with closed strips is the best option.

Three shading screens
If three screens are used, it is usually the combination of a plastic (fixed or mobile) screen with an energy screen and a shading screen. Another combination is an energy screen with two shading screens.

When combining a plastic screen, an energy screen and a shading screen, chalking with shading chalk can be useful because otherwise the temperature in the greenhouse can increase too much. With an energy screen with two shading screens, the temperature increases less, as a result of which it is not necessary to chalk. The only reason to chalk with this combination is when there are light strips in the greenhouse. This could be eliminated by means of a diffuse coating.

Another possible combination is that of an energy screen, a diffuse screen with open strips and an aluminium screen with closed strips. This combination saves you the most energy and incoming sunlight is kept to a minimum. The method explained above allows the use of PAR control (the screens are controlled according to the measured PAR light value in the greenhouse), because it is possible to provide variable shade with the two shading screens.

The last possibility is working with an energy screen as the lower screen in combination with two screens on one wire bed (duo screens). This can be a diffuse shading screen in combination with a shading screen with closed strips. An advantage is that a diffuse screen stops less light compared to a closed shading screen, so that it is possible to provide variable shade. An example is a 50% diffuse shading screen and a 50% shading screen (Tempa). The aforementioned combination allows you to fully benefit from the advantages in winter and summer. Thanks to the construction of two screens on the same wire bed, you avoid having to install an extra screen (that doesn’t close well) on the grid.

This article was written in collaboration with Bureau IMAC. If you require more information or additional advice, please contact Bureau IMAC.