Vienna deploys ‘Sponge Stones’ to help young trees through the dry summer

They will disperse rainwater over longer periods of time

Yesterday, the City of Vienna announced the introduction of innovative technology and what can be described as a ‘smart flagstone’ to get more water to trees and prevent a cycle of overwatering and drying out. This is the so-called Sponge Stone (Schwammstein) – a sustainable and carbon-neutral piece of equipment that can hold water and disperse it over time.

The Sponge Stone will be deployed on Flachgasse which is a densely built-up region of the Austrian capital. According to an official statement by the city, in recent years the failure rate of newly planted trees has grown due to swing weather, characterized by long periods of heavy rain versus drought. The Sponge Stone is supposed to balance these conditions out.

Integrated into the street pavement  

The Sponge Stones are made to integrate with the regular flagstones usually surrounding a tree bed on the sidewalk. Additionally, they always need to face the street to be able to collect rainwater flowing during rainy days.

Importantly, the mechanism has special sensors which stop collection during the initial water build-up, when the tree is already getting a lot of moisture. They will open up when street water levels go down and collect residual streams, which the mechanism disperses directly inside the tree bed over the next weeks.

Additionally, if the rain proves to be particularly long and persistent, the Sponge Stone’s valve would stay close to prevent drowning the tree. Also, if the temperatures are below 8 degrees Celsius, the device would remain closed as trees are dormant during the winter.

At the same time, the Sponge Stone will be powered by a small solar cell on its up-facing side, meaning that it would not need an additional power source and be completely carbon-free and self-sufficient.