Karlsruhe is watering by the numbers — with 100 Decentlab DL-SMTP sensors

Hotter summers and longer dry periods are making needs-based watering more important, and young trees feel it first — their root systems are still developing, which is what makes them so sensitive to drought.

Since July 2026, Karlsruhe's parks department has been running a trial on 100 young trees, the first step toward a city-wide network. The sensors sit in the root zone and measure continuously.

In the ground are 100 Decentlab sensors: the DL-SMTP | Soil Moisture and Temperature Profile for LoRaWAN®. Each measures moisture and temperature at six depths across a 600 mm profile. Six readings per tree instead of one, spread through the soil layers.

That distinction is doing the work here. According to the department, early results point to a pattern: watering tends to reach the upper soil layers, which dry out quickly in high temperatures. The deeper layers often receive too little — and those are exactly where a young tree's roots are meant to grow over time.

The data should show which trees actually need water, where watering is most urgent, and how long water stays available in each layer.

None of it replaces the watering can: the city still asks residents to help water during dry periods.

The soil looks watered. The profile shows where the water stopped.

More about the project