The problem with handheld moisture meters

While the popularity of handheld moisture meters for plants shows no signs of abating, there are some significant disadvantages for growers using this tool.

Handheld soil moisture and substrate moisture meters are a staple of every greenhouse grower’s toolkit. Every grower I know owns one or has owned one (or several) at some point. The popularity of “handhelds” stems from their portable nature, accuracy, and affordability.

Moisture meters have become an essential tool
Once manufacturers of soil moisture monitoring technology released a moisture meter that was small enough to be handled comfortably, robust enough to take a knock or two, and affordable enough for even the most cash strapped grower, the handheld meter secured its place on the list of essential tools for both commercial and domestic growers.

Portability also played a big part in the success of handheld moisture sensors. Having a battery-powered moisture measurement tool that most people could easily use kept equipment costs under control. Handheld units could be shared amongst multiple growing teams across shift changes or at multiple sites, so greenhouse growing operations could make do with just one or two units.

Despite these factors, handheld moisture meters have their downsides – particularly in greenhouse environments. The first of these is that handheld probes can only provide the grower with the current soil or substrate moisture reading – one from just a single moment in time. While growers may record many readings over the course of a day or week, these are typically taken only at the moment the reading is required. If notes are taken, they tend to be handwritten, making it difficult to analyze data over various time periods without consulting many sheets of paper. 

Whether growing in Rockwool, Coco Coir, or soil, growers want to consult their data and ask themselves: “How is the water content for my plants tracking?” 

  • This week

  • This month

  • Compared to last growing season

Paper records make answering these basic questions a long and slow process. 

Even with data entered into a spreadsheet (the input is time-consuming and subject to human error), it can be hard to achieve macro and micro views of moisture content readings without some additional (and often more involved) digital fiddling. 

Potentially vital data missing in between readings taken
Even growers who take soil moisture measurements 5 or 6 times a day are prone to missing events that may happen in between their scheduled moisture data recording. Should an irrigation pump fail, soil can quickly dry out with devastating effects. Crops like berries and cannabis quickly become irrecoverable after just a few hours, and if the failure event occurs between times when moisture readings are taken, growers can be unaware of the issue until it is too late.

Fragility of plant moisture probes remains a problem
The pins on a pin-type meter are vital components for gathering accurate soil-water content readings, but like most other tools in the greenhouse, they can be knocked, dropped, or trodden on, so careful handling and storage is key. Unfortunately, the portable nature of handheld meters means they are handled more frequently by more people, which increases the probability of the meter incurring some kind of damage.

You risk losing your moisture data
While this is not a risk specific to handheld moisture meters, it is worth noting that it only takes one corrupt file, a virus, an accidental deletion, or a file overwrite to lose months or perhaps years of data. Many growers are precariously positioned when it comes to the security and robustness of their file storage and data backup systems.

Inconsistency of location for repeated moisture sensor readings
Another issue is one of consistency of location. When using handheld meters, it’s unlikely you will press the probe into the exact same spot as the last time you took a reading. While this may not be of immediate concern, successfully growing crops is the product of the interplay between many variables, and so removing those that are unnecessary builds a more robust and repeatable process.

Additionally, greenhouse growers want to collect moisture readings from the same area as they are collecting other climate data.

Getting soil moisture data to work for you
The two biggest cons of using handheld moisture meters are the lack of continuous data and the difficulty in manipulating that data, both current and historic. Routing moisture readings to a data logger is one step towards addressing this, but a better and more forward-focused solution is connecting the moisture sensor data to the Cloud.

Once published to the Cloud, real-time data can be visualized as graphs or tables, while historic data can be retrospectively analyzed to spot trends, benchmark operations to track improvements, or study climate conditions that led to negative events like a pest or disease outbreaks.

Soil/substrate data can also be combined with climate data to build a better overall picture of climate conditions in the greenhouse. For example, photosynthesis, the process that plants use to grow, requires water, carbon dioxide, and light. Depending on the plant, this process is optimum at certain temperature and humidity ranges. By studying the data, the grower can learn what the limiting factor is. Too much light but not enough water won’t necessarily speed up photosynthesis and therefore growth.

Choosing the right moisture meter for monitoring your plants
The choices for greenhouse growers are:

  • handheld meters,

  • fixed meters with digital displays,

  • fixed meters coupled with data loggers; or

  • meters transmitting to the Cloud.

Hobbyists and small growers usually settle for the items earlier on this list as they tend to be cheaper, but larger commercial growers can also hang on to these for much longer than is useful – and is time-efficient to do so – simply put, the tool is no longer appropriate to the scale of their operations.

One climate monitoring solution that will scale as farm operations grow is the Folium sensor network. Folium sensors collect real-time climate and environmental readings and publish to the Cloud. This data is visualized as heatmaps, charts, or graphs to give growers a more holistic view of conditions in their growing environment.

An external moisture meter plugs into the base of the Folium sensor to provide continuous moisture readings from the growing media. Growers set alerts to be notified should soil/slab moisture readings fall outside their specified parameters, so they achieve greater consistency in managing irrigation.

Folium is a bluetooth wireless sensor and portable, and it can be located anywhere growers need to collect data. It collects readings of temperature, humidity, PAR, and RAD (two types of light), CO2, and barometric pressure. Additionally, external sensors such as a soil moisture or substrate moisture sensor, or a plant temperature sensor can be connected.

No more wasted time with handhelds meters
The saying “Old habits die hard” is never more true than in agriculture. If your farm staff is still spending hours walking the rows, taking plant readings with a handheld moisture meter and clipboard, you could be doing things better.

Improving farm management practices by leveraging technology like Folium sensor network saves labor hours and, therefore, labor costs. A small farm paying staff USD15 an hour, for example, could save at least 2 hours per day. Saving $30 per day doesn’t sound like much but equates to nearly $11,000 a year.

Coupled with a slew of other benefits, including greater awareness of potential disease outbreaks, dialing in conditions for optimum Integrated Pest Management (IPM), and having access to a growing body of data to make better decisions going forward means Folium sensor network is a wise investment for any grower serious about data-driven farming.

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