Pot plants: controlling growth through climate strategy
Climate strategies ‘Negative-Diff’ and ‘Cool morning/drop’
For ‘Negative-Diff’ the temperature set point at night is higher than during the day (Example: heating day/night 14/17 °C, ventilation day/night 16/20 °C). The plants grow more compactly in these conditions. This procedure, which has been used since the 1990s, is well documented. According to Hack it is primarily suited to the winter months. In the spring the radiation in the daytime can be so high that the procedure does not work well – according to Hack it is uncertain on 60 to 80 percent of the growing days. A sealed greenhouse with energy shielding and additional lighting is needed.
For ‘Cool morning/drop’ the temperature set point is lowered at sunrise, for example by 8°C. A climate computer is required. This weather-independent procedure can only be used in the spring and autumn and in the spring it can only be used on 30 to 50 percent of growing days. The plants grow more compactly and the procedure is energetically favourable in well-insulated greenhouses. In large departments there is a problem that individual sets or crops may react differently, explains Hack.
More than 100 nurseries use the ‘Weihenstephan model’
For the ‘Weihenstephan model’ cool mornings are combined with warm evenings, whereby the cool morning phase can be short or long. In Bavaria more than 100 nurseries are said to use this procedure, so that there is plenty of practical experience available. The plants grow more compactly and energy savings of 25 to 40 percent are possible according to Hack. The procedure depends on the weather and there can be problems with humidity. Warm evenings may increase the risk of botrytis at night. Also optimum implementation of warm evenings is considered complicated in practice.
Dry stress is another method to control crops in order to obtain more compact plants. A soil water tension of 40 to 120 hectopascal (hPa) is optimal for the plants. In some plants dry stress only has an effect at high soil water tension values (geraniums at over 200 hPa, petunias at over 105 hPa). If the cultivator subjects his or her plants to dry stress then even subsequent irrigation is important as growth differences could otherwise occur in the inventory. This procedure does entail a risk in this regard. Leaf burn can occur at high levels of radiation. According to Hack there are also still questions open regarding the rehydration of peat-reduced substrates.
New cultivation of pot plants
‘Het nieuwe telen’ (NGG, Next Generation Growing) is a concept from The Netherlands that refers to a reduction of carbon dioxide emissions based on 2015/16 levels – the aim is to reduce CO₂ by two or three percent every year. This is to be achieved through technical innovation and replacing fossil fuels. Growth conditions are optimised on the basis of consumption balance. Recipes derived from the evaluation of operations are to be realised using the climate computer.
According to Hack NGG is a continuation of the Zineg concept in principle, but more oriented towards the plant. The question is how NGG can be realised in Germany and how high the level of any investment would be.
Inhibitor savings
Motto: substantial inhibitor savings are possible by combining variety selection, temperature and irrigation strategies, particularly in specialised operation. In Hack’s opinion the complete abandonment of inhibitors is currently often associated with high risks and/or investments and thus cannot be realised.
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