Artificial light at night extends the growing season of urban plants

Light and temperature play a major role in influencing the growing seasons of plants. Due to the urban heat island effect, cities are getting hotter (higher air temperature) and brighter at night (artificial light at night or ALAN). Our knowledge is limited by climate change and urbanisation since it’s uncertain how heat and light affect phenology, the timing of plant growth events.

In a study recently published by Chinese, American and German researchers, including AquaPLAN researcher Franz Hölker from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (FVB-IGB), have shown that artificial light, together with urban heat, may be lengthening the growing season in urban environments by as much as 3 weeks compared to rural areas. Light pollution is also having a greater impact than urban heat, particularly at the end of the growing season. “This can put a strain on the energy and water balance of plants, which also have to contend with water shortages in increasingly dry cities“, said Franz Hölker, co-author and a leading expert on the ecological effects of light pollution. He added, “We expect the effects of artificial light on the growing season to increase even further in the future. This is because road lighting, for example, is currently being converted to LED lighting worldwide for energy efficiency reasons, which unfortunately often leads to higher illuminance levels due to rebound effects“.

Even small changes such as better alignment of the light by changing the luminaire design, adjusting the light intensity and wavelength, can significantly reduce light pollution. The results of the research carried out by Franz Hölker’s working group are being incorporated into the current drafting of a new legal regulation that minimises the negative effects on plants, animals and humans while meeting functional requirements.

Read the open access publication: Wang, L., Meng, L., Richardson, A.D., Hölker, F., Li, H., Mao, J., Longcore, T., Xia, J. and She, D. (2025). Artificial light at night outweighs temperature in lengthening urban growing seasons. Nature Cities. https://doi.org/10.1038/s44284-025-00258-2

Learn more, read the original FVB-IGB article