Every grower wants healthy plants. But how do you actually measure plant health? In many greenhouses, plant health is still judged mainly by visual signals such as leaf colour, plant strength or crop appearance. Experienced growers can read a lot from these signals, but visual observations alone rarely tell the full story.
Measuring Plant Health
From brix to plant sap analysis
Published: March 5, 2026
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Understanding plant health
Plant health is the result of a complex interaction between climate, water uptake, nutrient availability, photosynthesis and plant development. When one element changes, the others respond.
To better understand what is happening inside the crop, growers increasingly look beyond visual signals and start measuring the plant itself.
Plant sap analysis
One method that is gaining attention in greenhouse horticulture is plant sap analysis. Instead of analysing the soil or substrate, sap analysis measures the nutrient concentrations directly inside the plant tissue. This provides insight into how nutrients are actually taken up and used by the plant.
By analysing plant sap, growers can better understand:
- whether nutrient uptake is balanced
- how the plant responds to climate conditions
- if certain elements are accumulating or becoming limiting
- how plant metabolism changes during different growth stages
Because plant sap reflects the physiological status of the plant at that moment, it can provide valuable information about plant health and crop balance.
In the video below, we demonstrate how a plant sap analysis is performed and how growers can interpret the results.
This analysis is part of the Brix & Photosynthesis course, one of the modules within the Plant Health Year Program, where we explore different methods for measuring and understanding plant health.
Explore the Plant Health Year Program
Measuring plant health without expensive technology
One common misconception in modern horticulture is that measuring plant health requires advanced sensors or expensive robotics. In reality, growers can already learn a lot from consistent crop observation and simple measurements.
By spending a few hours per week in the greenhouse and registering a number of key parameters, it becomes possible to build a surprisingly accurate picture of plant balance.
Examples of useful measurements include:
- head thickness
- number of leaves
- internode length
- fruit set
- production levels
- fruit weight
When these parameters are tracked consistently over time, they provide valuable insight into how the crop responds to environmental conditions and management decisions.
Historical data becomes especially powerful. It helps growers recognise patterns and understand whether the plant is strengthening, weakening, or drifting out of balance. Plant sap analysis can then be used as an additional tool to look inside the plant, complementing these external observations.
Limiting the limiting factor
Plant performance is often determined by a limiting factor somewhere in the system. This may be light availability, root activity, nutrient uptake, or plant balance.
When the most limiting factor is reduced, the plant can use its energy more efficiently. In many cases, this is reflected in higher Brix levels, which indicate the concentration of sugars produced through photosynthesis.
However, Brix should not be seen as a goal in itself. It is better understood as a signal of the plant’s energy status and overall balance.
Understanding the plant as a system
Ultimately, plant health cannot be explained by a single measurement. Climate influences transpiration. Transpiration affects nutrient uptake. Nutrient uptake influences growth, resilience and crop balance. Understanding these connections helps growers interpret plant signals more accurately and make better crop steering decisions.
For growers who want to explore these relationships in more depth, topics such as Brix, photosynthesis and plant measurements are further explored in the Brix & Photosynthesis module, part of the Plant Health Year Program.
Because measuring plant health ultimately comes down to one principle: Understanding the dynamics of the plant system.
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