Plant irradiation during the germination period, by using environmental low level microwave radiation (known as electrosmog) alters the plant germination and the growing process. In order to analyze if such a subtle effect is generated only by the microwave irradiation, the environmental parameters (light, temperature, and humidity) must be kept identical for the reference and the irradiated lot. This is a difficult task because the humidity and temperature are interrelated. In order to study the plant behavior under microwaves low power irradiation, the paper describes the design, manufacturing and operating process and device performances on plant growth. To this end, a low power microwave field (average microwaves power density of 3.8 mW/m(2)) under controlled environmental parameters is used. The device consists of a reference chamber (R) and a microwave irradiation chamber (I), of 0.5 m(3) volume each one, equipped with access doors. The irradiation chamber ensures microwave field distribution with programmable power, frequency and bandwidth in the most commonly used standards for network communication such as: Global System for Mobile Communications (GSM900/1800), Code Division Multiple Access (CDMA), the third generation of mobile telecommunications technology (3G) or 2.4/5 GHz Wireless Local Area Network (WLAN). Both chambers provide a radiofrequency (RF) shielding (at least -60 dB) against and toward outside, so the electrosmog is shielded and does not interfere with the inner environment. Both chambers are equipped with performing temperature/humidity sensors and controlled LED lighting system (maximum 400 mu mol cm(-2) s(-1)) with a uniformity of +/- 5 mu mol cm(-2) s(-1) measured at the bottom level of the chamber. An embedded system (microcontroller) measures the temperature and humidity and proceeds continuously to match the humidity into the chambers pair with less than +/- 1.5% relative humidity (RH) difference, by using a low flux exhaust ventilation process through a simple innovative method. The accuracy of the temperature measurement is better than +/- 0.2 degrees C. Humidity and temperature data set are logged (with programmable acquisition rate) during the whole experiment and can be read later by a personal computer. To identify the influence of microwave treatment on bean seeds and plants development, three growing experiments were settled, based on 122 bean seeds each. The number of germinated seeds (determined each day during 8 days of experiment), the germination energy (GE [%]) of the seeds, the length of stems (SL) and roots (RL), the germination (G) [%], the seedling vigor index (SVI) and dry matter content (DM%) have been measured and computed. The obtained data showed significant increase for all parameters on microwave irradiation condition. (C) 2015 Elsevier B.V. All rights reserved.