KNOWLEDGE & TOOLS
Sap flow tells you how hard your crop is working. Stem diameter tells you whether it can sustain that work. This is what the second measurement makes visible.
What does a stem diameter sensor measure?
A stem diameter sensor measures the thickness of the stem continuously, accurate to a few micrometres. That thickness is not constant: during the day the stem shrinks because the plant transpires more water than it takes up, and at night it swells again as the reserves are replenished.
That daily rhythm tells you two things. The depth of the shrinkage shows how hard your crop is being pushed. The day-to-day difference shows how much it is actually growing. 2GROW measures this every 2.5 minutes with the PhytoStem sensor.
Answer block — deliberately short and factual, written to be quoted by AI search engines.
01
Not your estimate based on head thickness or leaf posture, but the measured increase in micrometres. Did your crop grow overnight, or did it stall?
How deeply the stem shrinks during the day tells you how much buffer is left. If that shrinkage deepens over several days, your crop is losing its reserve.
The ratio between overnight replenishment and net growth shows which way your crop is heading — the signal you steer on when pruning and setting fruit load.
02
The sensor clamps around the stem and stays there all season. It moves with the plant and registers every expansion and contraction.
03
Each of the two measurements has a blind spot. Sap flow shows what your crop is asking for, but not whether it can afford it. Diameter shows what is happening inside the plant, but responds more slowly to acute stress. Together they close each other's gap — and only then do you know not just that your crop is reacting, but why.
| Wat je ziet | Sapstroom | Diameter | Wat het betekent |
|---|---|---|---|
| Gewas onder druk | Hoog | Krimpt, groeit niet bij | Je plant teert op haar reserves. Verlaag de belasting of pas het klimaat aan. |
| Ruimte onbenut | Laag | Vult goed aan | Er is capaciteit over. Je kan actiever sturen op groei of productie. |
| In balans | Hoog | Vult 's nachts volledig aan | Je gewas werkt hard én herstelt. Dit is het patroon dat je wil vasthouden. |
| Opname stokt | Valt weg | Krimpt scherp | Waarschijnlijk een probleem bij de wortels of de gift, niet in het klimaat. |
Based on both parameters, 2GROW builds a forecast up to 48 hours ahead: over 95% accurate for sap flow and over 70% for diameter. That lets you steer before things go wrong instead of explaining them afterwards. Also read what sap flow actually measures.
04
What unit is stem diameter measured in?
In micrometres (µm), thousandths of a millimetre. The daily shrinkage and swelling of a tomato stem is typically in the order of a few hundred micrometres — invisible to the eye, easily measurable for the sensor.
Does the sensor damage my plant?
No. The sensor clamps gently around the stem and moves with the growth. The plant stays productive all season and nothing needs to be moved.
How many measuring points do I need?
One measured plant already gives you insight into why your crop reacts the way it does. To actively steer at compartment level, we work with several measuring points per compartment — in practice usually three sensors.
Is stem diameter the same as measuring crop growth?
It is the most direct indicator you can measure continuously. Where weighing or counting gives you an outcome after the fact, the diameter curve shows every night whether your crop is growing or standing still.
Can I measure diameter only, without sap flow?
You can, and it delivers valuable growth information. Most growers combine both because one explains what the other shows: sap flow gives the demand, diameter gives the carrying capacity.
In a 30-minute intro call we show diameter and sap flow curves from a crop like yours — and what a grower actually did with them.
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