News » 10.07.2026 - Lower humidity improves stomatal function in chrysanthemum
As greenhouses become more energy-efficient, effective humidity management becomes increasingly important. Transpiration requires energy, but too little of it can lead to quality problems. Under the Masterplan Verdamping (Transpiration Masterplan), Plant Lighting is investigating how growers in the Netherlands can save energy without compromising the quality of chrysanthemums. Stefan van den Boogaart presented the results as part of the Kas als Energiebron (Greenhouse as a Source of Energy) program.
The research focuses on how relative humidity (RH) affects transpiration and stomatal function. Stomata, the small openings in leaves, play a key role in both CO₂ uptake and plant transpiration. Earlier research showed that prolonged high humidity can cause stomata to function less effectively, becoming what researchers describe as "lazy." Two recent climate trials examined whether temporarily lowering humidity, either during the day or at night, could prevent this effect.
Lower RH stimulates evaporation
In the first trial, a continuous high relative humidity of 95% was compared with a scenario in which daytime RH was reduced to 79%. The effect was immediate: transpiration was around 50% higher under the lower RH regime, at 1,400 millilitres per square metre per day compared with 950 millilitres. This difference occurred entirely during daytime hours; no difference was measured at night.
A second trial examined the effect of lower RH specifically at night, along with whether additional air movement at the top and bottom of the crop could further stimulate transpiration.
Under continuous high RH, extra air movement produced a limited increase in transpiration, equivalent to a rise of around 25%. When RH was lowered, transpiration increased by approximately 35%. Air movement at the bottom of the crop proved more effective than at the top.
Stomata function better
The main conclusion from both trials is that lower RH, whether during the day or at night, results in better stomatal function. This confirms earlier findings that prolonged high humidity is a key cause of stomatal dysfunction.
Notably, additional air movement on its own had little effect on stomatal function. Although it increased transpiration, it barely improved how the stomata worked. This suggests that the amount of transpiration is not the only relevant factor — the humidity level under which that transpiration occurs is equally important.
Follow-up research
This unexpected finding will be explored further in follow-up research, which will also examine whether there is a specific stage in the crop cycle when stomata are particularly sensitive to high humidity.
If this sensitive phase turns out to occur only early in cultivation, it could open up practical opportunities for growers. In that case, growers could maintain higher humidity levels during the second half of the cultivation cycle, reducing the need for heating and saving energy without affecting crop quality.
Funding and coordination of the research
The Masterplan Verdamping is part of the broader research project "Transpiration and moisture balance of plant and greenhouse in energy-efficient cultivation." The program is a collaboration between the Greenhouse Horticulture business unit of Wageningen University & Research, Delphy Improvement Centre, Plant Lighting and Glastuinbouw Nederland, with funding from the Topsector Tuinbouw en Uitgangsmaterialen and the Stichting Kennis in je Kas (KijK) foundation.
Within the Topsector program, businesses, research institutions and government bodies collaborate on innovations in the sustainable production of healthy, safe food and the development of a healthy, green living environment. This research was carried out as part of Kas als Energiebron, the innovation and action program run by the Dutch Ministry of Agriculture, Fisheries, Food Security and Nature (LVVN) and Glastuinbouw Nederland.
Source: www.floraldaily.com
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