Strawberries are one of the crops where “almost right” with water quickly becomes too much or too little. The root system is shallow, substrate aeration matters as much as water, and the fruit responds immediately to swings: uneven sizing, tip burn, soft berries, or diluted flavor. That’s why irrigation is managed more safely by measurement, not by a fixed schedule.
In substrate (grow bags, pots, gutters/tabletop), the available water volume is small and changes fast with light, temperature, and ventilation. At the same time, high air humidity and condensation increase Botrytis pressure, especially when leaves stay wet after late irrigations or after cold nights. Here VPD becomes a useful indicator of the crop’s “evaporation demand.”
This article explains the technical fundamentals (substrate, VPD, EC/pH) and a commissioning workflow that leads to relevant irrigation alerts. It does not impose one irrigation recipe for all farms; it shows how to build thresholds from measurements, crop observations, and independent checks (drainage, substrate extract, and row inspections).
1) What “correct irrigation” means for strawberries in substrate
Mechanism: in substrate you have a narrow window between lack of water (fast stress, reduced nutrient uptake) and excess (low oxygen at the roots, higher disease risk, softer fruit). Strawberries need relatively uniform moisture in the active root zone, but with air-filled pores still available. That’s why you should not track only how much water you apply, but how moisture moves over time and across zones.
What to observe: slightly drooping leaf tips in the afternoon, small or misshapen fruit can signal deficit; soft peduncles, watery fruit, or an anaerobic smell in a bag can signal excess. What to verify independently: measure drainage (volume and timing), weigh one bag/pot as a spot check, or cut/inspect substrate to see where it is wet or dry. Practical decision: adjust irrigation frequency and timing. Result check: the moisture curve returns to a stable rhythm without large swings between irrigations.
2) Substrate and the “language” of sensors: what are you actually measuring?
Mechanism: substrate moisture sensors may report volumetric water content or a correlated value (depending on technology). What matters is to treat the data as trends and locally commissioned thresholds, not as universal truth. In different substrates (coco, peat, mixes), the same reading can mean different water availability and different aeration. Commissioning therefore starts by linking sensor–substrate–crop behavior.
What to observe: after an irrigation, moisture should rise quickly; between irrigations, it should decline gradually, faster on bright days. What to verify independently: a simple “irrigation–drain” test in a representative zone to confirm the sensor responds and that drainage occurs when you expect it. Practical decision: define two operational thresholds per zone (too dry / too wet) based on plant response and drainage, not copied numbers. Result check: alerts become rare and explainable, not daily noise.
3) VPD in strawberries: why it helps, and what it cannot tell you
Mechanism: VPD (vapor pressure deficit) is an estimate derived from air temperature and relative humidity; it describes how strongly air can take up water vapor. When VPD is low (cool/humid air), transpiration drops, plants use less water, and leaves stay wet longer. When VPD is high (warm/dry air), water use rises and the substrate can empty quickly between pulses.
What to observe: during low VPD periods, morning condensation and wet leaves are more common; during high VPD periods, tips may temporarily wilt and calcium delivery to fruit can become harder if flow is reduced or unstable. What to verify independently: check leaf wetness (wet/dry), actual temperature at canopy height, and any difference versus air (leaf temperature can differ). Practical decision: use VPD as context for irrigation and ventilation, not as a rigid setpoint. Result check: leaf-wetness duration decreases without forcing unnecessary irrigations.
4) Choosing and placing sensors: zones, edges, and the “active root” volume
Mechanism: in low tunnels, greenhouses, and tabletop systems, edges and row ends dry differently than the center due to drafts, radiation, and shading differences. If you install a single probe “where it’s convenient,” you will tune irrigation to a non-representative area. A substrate probe must sit in the volume actually colonized by roots, not pressed against the dripper and not at the bottom of the bag where water accumulates.
What to observe: vigor differences between edge rows and central rows; higher drainage in one area and almost none in another. What to verify independently: open a sample bag/pot to identify root distribution; check dripper uniformity (approximate flow) and their position. Practical decision: define at least two monitoring zones (edge vs center) and choose comparable points by cultivar, plant age, and exposure. Result check: zone graphs differ in a logical way, and your decisions become zone-specific rather than “average-based.”
5) EC and pH in fertigation: the difference between water, solution, and substrate
Mechanism: EC and pH are not inferred from temperature or moisture; they require dedicated probes and must be interpreted by measurement medium. EC of irrigation water, EC of fertigation solution, and EC from a substrate extract are different measurements with different meaning. Also, EC indicates total dissolved salts; it does not tell you which nutrient is missing or excessive. pH shows the direction of nutrient availability but does not replace analysis.
What to observe: rising substrate EC after periods of high evaporation or insufficient drainage; pH fluctuations when the water source or recipe changes. What to verify independently: a water analysis that separates pH, alkalinity, and soluble salts, and periodic comparison of on-site readings with a lab or a consistent standard extraction method (same procedure each time). Practical decision: adjust drainage management and fertigation consistency before aggressively “correcting” the recipe. Result check: EC/pH trends stabilize and unexplained spikes become less frequent.
6) Commissioning workflow: from raw data to thresholds that truly help
Mechanism: commissioning means proving sensors read coherently, that the reporting interval is fresh enough for decisions, and that alerts match reality. In the first 7–14 days, you do not “optimize” yet; you build a baseline. In GrowGuard, you track zone history and correlate events (irrigation, ventilation, cloudy days) with the response of substrate moisture and VPD.
What to observe: delays between irrigation and moisture increase, suspicious plateaus (a probe with poor contact), or sudden jumps (probe removed/moved). What to verify independently: compare two nearby points (same zone) and run a controlled test—one short irrigation at a fixed time, then watch the response over the next 30–60 minutes. Practical decision: choose conservative initial alert thresholds (too dry/too wet, very low VPD) and refine them based on observations. Result check: alerts occur when there is an identifiable cause.
7) Irrigation alerts: avoiding “false alarms” and autopilot routines
Mechanism: a common mistake is keeping the same irrigation recipe on cold, hot, and cloudy days even though crop water use changes strongly. Alerts should capture these changes: rapid moisture drop on a very hot day, or persistently high moisture during a cold period with low VPD. Instead of a single threshold, think in conditions: low moisture + high VPD means something different than low moisture + very low VPD.
What to observe: repeated night alerts (usually thresholds too tight) or no alerts on a day with visible stress (usually thresholds too wide or sensor poorly placed). What to verify independently: manually note 3–5 days with different conditions (cloudy, hot, cold) and compare with graphs; check whether alert timing makes sense versus the irrigation schedule and ventilation events. Practical decision: separate alerts by zone and by time window (for example, different sensitivity day vs night). Result check: fewer ignored alerts and a higher rate of justified actions.
8) Post-intervention diagnosis: confirming the decision was correct
Mechanism: without a post-intervention check, you risk “correcting” in the wrong direction. After changing irrigation or ventilation, follow both fast responses (substrate moisture, VPD) and slow indicators (size, firmness, uniformity, disease appearance). In strawberries, excess water can mask a temporary deficit (plants look turgid) while harming roots and quality over time.
What to observe: if you increased irrigation frequency, you should see smaller drops between pulses; if you reduced irrigation during a cold period, moisture should not remain “high” for days. What to verify independently: check drainage at a few points and inspect roots (color, smell), plus morning leaf condition (condensation). Practical decision: keep the change only if indicators improve within 2–5 days (hypothetical). Result check: trends become stable and symptoms reduce rather than shifting into a different form.
Conclusion
Correct irrigation for substrate strawberries is a combination of physics (water–air in a small volume), physiology (transpiration and nutrient transport), and microclimate (VPD and condensation). Sensors are useful only when placed in the active root zone, interpreted by zones, and validated with simple checks: drainage, root inspection, leaf observations, and row-to-row comparisons.
To start practically, first set representative points (edge/center), run one week of baseline data, then refine thresholds so alerts reflect real demand changes or excess-risk conditions. In GrowGuard, use history and alerts as a commissioning and verification routine. If you want a workflow adapted to your farm, request a zone-based setup with the technical team.