It is quite well known that it is difficult for a rose crop to continue growing and producing quality flowers under high radiation and temperature conditions. Both leaf- and flower temperature might increase dramatically under such conditions, resulting in stress and loss of color in the flowers. Precautions should be taken under such weather conditions to ensure uninterrupted growth and optimum quality. For instance, several growers apply white wash on their roofs for a few weeks or for several months. Others try to increase the humidity and decrease the temperature by means of mist systems or roof sprinklers.
More and more growers have decided to invest in a movable Svensson® screen to improve the climate during the summer season. As Svensson® screens reflect part of the sun radiation back through the plastic or glass of the roof, they lower both ambient and crop temperatures considerably.
The Problem
During hot and sunny weather conditions a rose plant tries to cool itself down by transpiration of water through the leaves. This is, however, a process with a certain maximum capacity. During extreme light and temperature conditions it is not enough to keep the plant temperature under control. As a result, leaf temperatures reach very high levels, resulting in slower growth and sometimes even burning.
A high transpiration rate, taking place at high radiation and temperature levels, is important for the cooling of the crop. When it lasts too long, however, it might result in a stunted growth, as the leaves withdraw water from other parts of the plant like the growing point and the stem. This results into a stocky crop and shorter flower stems with a lower selling price. The flower buds are in an even more delicate position, as they do not have the ability to cool themselves through transpiration. Thus, sun radiation, falling on the buds, is transformed completely into heat, significantly increasing their temperature, easily 5 °C above that of the surrounding air. Flower buds of dark red cultivars like First Red, Grand Prix and Red Berlin are especially sensitive to this. The result is a decline in quality and a loss of color.
The solution
It has been proven that reflective Svensson® screens help solve the above problems to a large extent. Growers in The Netherlands, France, Italy, Israel, and USA and around the globe have experienced great improvements in their crop growth and flower quality by using one of the screens provided by Svensson.
Svensson® screens are made of pure aluminium strips, combined with light transmitting polyester or open strips. The aluminium strips reflect nearly 100% of the sun radiation upwards so that less sun and heat radiation falls on the crop. The result is a considerable decrease in air and crop temperature. At the same time the transpiration rate returns to more normal levels. Energy is spent on growth rather than maintenance.
The overall effect of using the screen is:
1. A better flower colour
2. Less leaf burning
3. Longer flower stems
4. Quicker development of new flower stems
The effect of Svensson® screens on the inside temperature is clearly illustrated in the following graph. It shows the temperature inside the greenhouse using XLS 14 F FIREBREAK shade screen. This screen reflects 41% of the sun and it has an open structure. This allows the air to pass through the screen, so that the ventilation through roof vents is not hampered.
Closing the screen at around 10:30 a.m. lowers the inside air temperature by up to 5 °C less than with no screen.
No whitewashing anymore
Rose growers who don't use a reflective Svensson® screen often apply whitewash on the roof in order to reduce the incoming radiation. Although being effective in lowering the inside temperature it is considered not to be an optimum solution. The whitewash is permanent, so it also cuts down the incoming light during overcast conditions and during early morning and late afternoon hours. Cutting down the light intensity during such times is not beneficial to the crop. To an extent, it lowers the growth potential of the roses. Those growers who have invested in a movable Svensson® screen could eliminate whitewashing the roof and by this, increase the amount of light available for the crop, by at least 20% over having a permanent of fixed shade level.
Roof sprinklers and mist systems
Screens are not the only means to solve overheating and crop burning. Growers often use a combination of screens, mist systems and/or roof sprinklers. The combined effect not only gives a
considerable decrease in the temperature but, simultaneously, an increase in the air humidity.
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