I’ve been reading Dr. Lynette Morgan’s articles in Maximum Yield for some time, and I’m interested in getting her thoughts on which sensors are needed for aeroponic growth chambers. I know temperature and humidity are crucial. I imagine lux meters are useless since the root chambers should be dark. Would she recommend O2, CO2 and leaf sensors, or would that be overkill? Would leaf sensors be enough to render the other sensors redundant? Would O2 and CO2 sensors only increase yields marginally and therefore make their cost unnecessary? I’m trying to achieve good yields without buying all the sensors out there. I already have EC, pH and light sensors outside the growth chamber.

There are a wide range of sensors that could be used in an aeroponic growth chamber, but the objective is to use only those that will give relevant information that you can use to influence growth.

In the misting chamber, which should be kept completely dark, keeping track of temperature is essential, as root temperature determines important processes such as nutrient uptake and respiration. With aeroponic misting, assuming you have a regular or continual misting program that does not let the roots dry out, there will always be sufficient oxygen, as the roots are hanging in saturated air, which is typically close to 100% humidity and misted with a highly oxygenated solution, so measuring humidity and oxygen in the root chamber is generally not necessary. Sensors are of more use for the aerial portions of plants. The foliage responds to CO₂ when lights are on, and temperature, humidity and light and the interaction of these factors is what drives growth via photosynthesis. Light can be measured as PAR (photosynthetically active radiation) with light sensors so the intensity can be checked, but using DLI (daily light integral) sensors can also be beneficial, particularly if you vary the day length as the plant grows. CO₂ sensors placed into the plant canopy are also valuable tools, whether you are enriching with CO₂ or not. CO₂ depletion can occur rapidly with large, mature plants growing under intense lighting conditions and sensors are the only way of tracking levels during the light period and ensuring levels are optimal.

For leaf surfaces, a non-destructive infrared thermometer is a cost-effective tool for measuring leaf temperature. Measuring in several locations at the same time can determine if plants are actively photosynthesizing, as it can be difficult to determine if photosynthesis has shut down. Photosynthesizing plants will have their leaf stomata open for CO₂ absorption, and open stomata transpire and cool the leaf surface, so plants are photosynthesizing if the leaf surface is a few degrees cooler than the actual air temperature. If the leaf surface is the same temperature or slightly higher than the air temperature, it’s the stomata have likely closed to conserve water. This is far more common than many growers realize.

As for moisture measuring tools, leaf turgor sensors, which can be quite expensive, can be used as a backup if the misting system fails or misting frequency is not sufficient to meet the needs of the plant as it grows. The grower can be notified with a warning message or the sensor can be used to control an increase in irrigation as required.