Why pH Control is Critical in Fertigation and Irrigation Systems

Irrigation quality, is made up of many areas, flow rates, uniformity, filtration, water quality, volumes, pressures, timing, monitoring and control. flow rates,. But one of the biggest factors influencing plant health — and often the most overlooked — is pH control.

1. pH Determines What Nutrients Your Plants Can Actually Use

Plants don’t absorb nutrients just because they’re present in the water or fertiliser tank. They absorb nutrients only when those nutrients are in a chemically available form — and pH is what controls that.

• At the wrong pH, key elements like iron, manganese, zinc, and phosphorus become locked up.

• Even if you’re applying the right fertiliser, the plant can’t access it.

• The result: deficiency symptoms, slow growth, and wasted inputs.

• Correct pH = maximum nutrient availability.

How pH Affects Each Nutrient

The availability of individual nutrients in the root zone is strongly influenced by pH. At the wrong pH, nutrients that are present in the solution chemically bind with other compounds and become unavailable to the plant — a phenomenon known as nutrient lockout.

• Nitrogen (N) — available across a wide pH range but most efficiently absorbed between pH 6.0 and 7.0. At high pH, ammonium-based nitrogen can volatilise.

• Phosphorus (P) — highly pH-sensitive. Availability peaks between pH 6.0 and 7.0 and drops sharply outside this range. At high pH, phosphorus binds with calcium and magnesium to form insoluble compounds. At low pH, it binds with iron and aluminium.

• Potassium (K) — relatively stable across a broad range but uptake is most efficient between pH 6.0 and 7.5.

• Calcium (Ca) and Magnesium (Mg) — availability decreases at low pH. Calcium deficiency at low pH is a common cause of tip burn in lettuce and blossom end rot in tomatoes.

• Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B) — micronutrients that become more soluble at lower pH. At high pH (above 7.0–7.5), these can become severely locked out even when present in the feed solution.

• Molybdenum (Mo) — the exception: availability increases with rising pH and can become deficient at low pH.

2. pH Affects Fertiliser Stability

• Many fertilisers react differently depending on the acidity or alkalinity of the water.

• High pH can cause precipitation — nutrients turning into solids that block emitters and drippers.

• Low pH can cause over-availability, leading to toxicity or nutrient imbalance.

• Stable pH keeps your A/B mixes consistent and predictable.

3. Irrigation Water Isn’t Neutral — And It Changes

Borehole and mains water often arrive with a naturally high pH due to dissolved bicarbonates. As water warms, oxygenates, or mixes with fertiliser, pH can shift again.

That’s why pre-dosing and real-time pH control are essential. They stabilise the water before it reaches the crop, giving your fertigation system a consistent starting point. Most UK mains water sits between pH 7.0 and 8.5 — well above the optimal range for most crops — meaning acidification is required in the majority of UK growing operations.

Optimal pH Ranges by Crop

For most horticultural crops, the target pH range for the irrigation solution is 5.5 to 6.5, with many crops performing best between 5.8 and 6.2.

• Tomatoes, cucumbers, peppers — pH 5.8–6.3

• Lettuce and leafy crops — pH 5.5–6.0

• Strawberries — pH 5.5–6.0

• Herbs — pH 5.5–6.5

• Ornamentals and bedding plants — pH 5.8–6.5

• Soft fruit (outdoor) — pH 6.0–6.5

4. Better pH = Better Root Health

Roots thrive in a narrow pH window. Outside of it:

• Beneficial microbes decline

• Root efficiency drops

• Stress increases

• Growth slows

Maintaining the correct pH keeps the root zone active, balanced, and able to take up nutrients efficiently. In soil systems, pH also affects the microbial community that supports nutrient cycling — another reason why pH management matters beyond just the chemistry of the solution itself.

5. pH Control Saves Money

When pH is wrong, growers often compensate by adding more fertiliser — but the plant still can’t use it. Correct pH means:

• Less fertiliser waste

• More efficient feeding

• Better crop performance

• Higher uniformity across the site

In short: pH control isn’t optional — it’s the foundation of effective fertigation. Whether you’re running a small holding or a large commercial greenhouse, stable pH is one of the biggest contributors to crop performance, nutrient efficiency, and long-term system health.

How pH is Corrected in Fertigation Systems

pH correction in irrigation is achieved by dosing an acid into the water stream. The most commonly used acids in horticulture are:

• Nitric acid (HNO₃) — the most widely used in commercial horticulture. Has the advantage of contributing nitrogen to the feed solution.

• Phosphoric acid (H₃PO₄) — contributes phosphorus. Useful where phosphorus demand is high but can cause precipitation issues at high concentrations.

• Sulphuric acid (H₂SO₄) — low cost but contributes sulphate, which can accumulate in recirculating systems.

• Citric acid — used in organic systems. Less stable and more expensive than mineral acids.

Automated pH Control: How It Works

A fully automated pH control system consists of three core components:

1. pH sensor — continuously measures the pH of the irrigation solution in the pipeline or mixing vessel.

2. Controller / transmitter — reads the sensor signal, compares it to the target setpoint, and triggers the dosing system when correction is needed.

3. Dosing mechanism — a venturi injector or dosing pump that introduces acid into the water stream in response to the controller signal.

The system operates as a closed-loop control: the sensor measures, the controller calculates the correction needed, the dosing mechanism responds, and the sensor confirms the result. This cycle repeats continuously, maintaining pH within a tight band around the target setpoint regardless of changes in source water quality or fertiliser concentration.

pH Control Products from IrriSmart

Senmatic AMI Simplex with pH Control

The Senmatic AMI Simplex is a professional fertigation machine that can be specified with optional pH control. By adding a venturi and pH sensor, the AMI Simplex continuously monitors and regulates the pH value of the fertigation solution — automatically dosing acid to maintain the target setpoint. It supports up to 3 fertiliser groups, each with 4 individual recipes specifying EC, pH, and fertiliser mix.

• AMI Simplex 15 m³/h — suitable for small to medium growing operations

• AMI Simplex 25 m³/h — for larger commercial operations

• pH Control Expansion — adds automated pH dosing to the AMI Simplex

JUMO pH and EC Sensors

The JUMO EC/pH Sensors are precision measurement sensors for integration into fertigation and irrigation monitoring systems.

• JUMO pH Sensor — 12mm Glass with BNC Connection (SKU: 45000-006692) — glass-bodied pH electrode for accurate, stable pH measurement in irrigation pipelines

• JUMO EC Sensor with Temperature Compensation PT100 — 12mm (SKU: 45000-006705) — EC sensor with integrated PT100 temperature compensation

EC/pH Union Adaptor Set

The EC/pH Union Adaptor Set (SKU: 33140-008500) provides the correct pipe union fittings for installing JUMO sensors into the irrigation pipeline — ensuring a secure, leak-free connection and correct sensor positioning in the flow.

EC/pH Transmitters

• EC/pH Monitor — 24V Wall Mount (SKU: 74340-003580) — wall-mounted transmitter compatible with JUMO sensors and Senmatic controllers

• GS EC/pH Transmitter — AWT420 Wall Mount (SKU: 74360-007901) — advanced transmitter for Growsphere-compatible systems

Senmatic AMI Penta pH and EC Sensors

For operations using the Senmatic AMI Penta platform, dedicated sensor and transmitter combinations are available via the Senmatic Sensor range:

• pH Sensor + Transmitter AMI Penta (SKU: 590010)

• EC Sensor 2 + Transmitter AMI Penta (SKU: 590080)

EC and pH: Working Together

pH control works alongside EC (electrical conductivity) monitoring to give a complete picture of the fertigation solution. EC measures the total dissolved salt concentration — a proxy for overall nutrient concentration. pH tells you whether those nutrients are in a form the plant can actually absorb.

• EC too low — the plant is being under-fed

• EC too high — osmotic stress, root damage, and reduced water uptake

• pH too high — micronutrient lockout, phosphorus deficiency, poor iron availability

• pH too low — calcium and magnesium deficiency, potential root damage, manganese and aluminium toxicity in soil systems

Sensor Maintenance and Calibration

pH sensors require regular calibration to maintain accuracy. Best practice:

• Calibrate regularly — at minimum at the start of each growing season, and ideally monthly during active production. Use two-point calibration with pH 4.01 and pH 7.01 buffer solutions.

• Store correctly — glass pH electrodes must be stored in storage solution or pH 7 buffer, never in distilled water or dry.

• Clean the electrode — fertiliser salt deposits and biological growth can coat the electrode and affect accuracy. Clean gently and rinse with clean water before calibrating.

• Replace when necessary — glass pH electrodes typically last 1–2 years in continuous use. Slow response time or inability to calibrate accurately are signs that replacement is needed.

Need Help with pH Control for Your System?

Whether you’re looking to add automated pH control to an existing fertigation system, specify a new system with pH management built in, or need replacement sensors and calibration equipment, the IrriSmart team can help. Get in touch to discuss your requirements.

Browse our Senmatic DGT Systems & Spares collection for the full range of fertigation control and monitoring products.