Reliable communication is crucial for successful deployment of wireless sensor networks. Therefore, it is important to understand the impact of environmental conditions on the performance of the radios (Chipcon CC1000 transceivers) used in typical sensor nodes. This paper reports on an extensive set of measurements taken in a potato field, where the foliage has an important effect on the propagation of radio waves. The influence of the growth stage of the potato crop is significant. We observed a reduction of 15 dB in signal strength at 15 m between nodes, when a flowering crop is compared to a crop on its return. This effectively reduces the radio range from 23 m to 10 m. Another important result is that radio waves propagate better in conditions with a high humidity (i.e., at night and during rain). We attribute this to changes in the reflection coefficient of the top of the potato canopy.