Understanding Hydroponics
Plants are cultivated without natural soil, either in substrates or directly in a controlled nutrient solution. Successful operation does not depend on isolated ideal values, but on coordinated management of water, nutrients, the root zone, climate, light and hygiene.
1. What hydroponics is—and what it is not
Hydroponics is a form of soil-free cultivation. Roots grow in an aqueous nutrient solution or in a substrate used primarily for structural support and supplied by irrigation. Water and mineral plant nutrients are delivered in a controlled manner; depending on the design, the solution is recirculated, temporarily retained or discharged after a single use.
Hydroponics
An umbrella term for soil-free production methods with controlled water and nutrient supply.
Hydroculture
In everyday German usage, this generally refers to passive indoor-plant cultivation, often in expanded clay. It is not synonymous with professional hydroponics.
Aquaponics
Combines crop production with aquaculture and biological treatment. Its nutrient source and operational trade-offs differ from those of mineral hydroponics.
Important: “Without soil” does not mean “without a root zone”, “without microorganisms” or “without residues”. Hydroponic systems also require robust hygiene, water-management and disposal strategies.
2. The path of the nutrient solution
Plants do not absorb water and ions in the same proportions. An apparently suitable EC reading therefore cannot rule out an imbalanced nutrient composition. Source water, formulation, top-up water, plant uptake and the remaining solution must be assessed together.
3. pH, EC, temperature and oxygen
| Parameter | What it indicates | What it does not indicate | Operational task |
|---|---|---|---|
| pH | Acidity and therefore an important influence on nutrient solubility and uptake. | No complete information about the quantities of nutrients present. | Assess the crop, formulation, alkalinity and root zone together. |
| EC | The combined effect of electrically conductive dissolved ions. | Neither individual concentrations nor a reliable nutrient balance. | Track the crop-specific target range and trend; calibrate the meter. |
| Temperature | Affects root respiration, growth, solubility and disease risk. | No universal target value for every crop and system. | Record water and air temperature as well as changes throughout the day. |
| Dissolved oxygen | The availability of oxygen in the solution. | No direct information about every location within the root zone. | Coordinate aeration, flow, temperature, biomass and resilience to failure. |
Guidelines are not release criteria: Frequently cited ranges such as approximately pH 5–6.5 or crop-dependent EC ranges are starting points. The specific operating strategy depends on the cultivar, growth stage, water, climate, measurement method and system design.
4. Comparing hydroponic systems
| System | Principle | Strength | Critical point | Typical suitability |
|---|---|---|---|---|
| Kratky / non-circulating | A falling solution level creates a humid air space around part of the roots. | Very little equipment and no continuously operating pump. | Limited scope for intervention; container size and crop duration must be compatible. | Leafy vegetables, demonstrations and small batches. |
| DWC / deep-water culture | Roots remain suspended in aerated nutrient solution. | Large water buffer and uniform supply. | Aeration or temperature failures affect the entire crop. | Lettuce, herbs and larger uniform production runs. |
| NFT | A thin film of nutrient solution flows through gently sloping channels. | Low water volume around the roots and efficient use of space. | Pump failure, blockages or an incorrect gradient can rapidly become critical. | Lightweight crops with a manageable root volume. |
| Flood and drain | The substrate or growing table is periodically flooded and then drained. | Alternating nutrient supply and aeration; flexible choice of containers. | Drainage, salt distribution, pump control and hygiene. | Propagation, container crops and a variety of substrates. |
| Drip irrigation / Dutch bucket | Nutrient solution is metered to each plant or container. | Individual dosing and suitability for large fruiting crops. | Blocked emitters, drainage control and salt accumulation. | Tomatoes, cucumbers, peppers and other fruiting crops. |
Vertical systems do not have a separate nutrient logic. They arrange DWC, NFT, drip irrigation or other irrigation principles above one another and therefore place greater demands on light distribution, pressure, maintenance access, uniformity and occupational safety.
5. Selection guide
1. Define the crop
Determine its growth habit, cultivation period, root volume, support needs, temperature, light and harvesting method.
2. Assess the site
Record load-bearing capacity, water quality, power supply, heat, ventilation, drainage, hygiene zones and working routes.
3. Evaluate downtime
How quickly will the crop suffer if pumping, aeration, cooling or dosing fails?
4. Calculate labour
Measuring, calibrating, cleaning, harvesting, replanting and record-keeping are all part of system performance.
5. Balance material flows
Do not omit water, fertiliser, residual solution, substrates, packaging, energy or waste.
6. Validate at small scale
Test the formulation and operating method first in a manageable unit under real conditions.
6. Select suitable plants
Leafy vegetables and herbs generally have short cultivation periods and place less load on support structures. Fruiting vegetables require long-term stability, support, pollination management, more light and careful provision of potassium, calcium and other elements. The key question is not merely whether a plant can grow hydroponically, but whether the system, climate, quality requirements, harvesting method and market are compatible.
No universal list: Crops with markedly different climate, EC or developmental requirements should not be connected to the same circuit solely to save space.
7. Clean processes instead of a “sterile system”
Waterborne pathogens can spread rapidly through interconnected systems. Prevention begins with healthy plant material, separate clean and contaminated routes, light-proof pipes, prompt removal of plant debris, cleaned tools and documented replacement intervals.
UV treatment, filtration, heat and other forms of water treatment are possible process stages, but they are not universal substitutes for identifying the underlying cause. They must be designed with due regard to flow rate, water turbidity, organisms, material compatibility, occupational safety and applicable legislation.
8. Failures and redundancy
| Failure | First priority | Prevention |
|---|---|---|
| Pump failure | Safeguard root supply and prevent backflow. | Alarm, spare pump, bypass and accessible shut-off valves. |
| Aeration failure | Restore the oxygen supply, particularly in DWC. | Independent emergency aeration and load testing. |
| Dosing error | Stop dosing and verify the readings independently. | Dosing limits, separate concentrates, calibration and approval procedures. |
| Leak / overflow | Limit the water supply and prevent electrical hazards. | Secondary containment, level alarm, emergency drain and suitable floor drainage. |
| Root disease | Isolate the affected unit and determine the cause. | Quarantine, cleaning, temperature control and oxygen management. |
9. Advantages and limitations
Potential advantages
- targeted management of water and nutrients
- production without suitable agricultural soil
- high space efficiency for suitable crops
- controllable working and harvesting processes
System limitations
- technical, measurement and specialist expertise required
- rapid consequences from interconnected failures
- energy demand for lighting, climate control and pumps
- residual solutions and substrates remain material flows
Fair assessment
- compare the same crop and product quality
- account for location and climate
- record water, energy and operating inputs
- assess yield and losses together
No universal percentage: Water and space efficiency depend on the reference basis, crop, yield, recirculation, cleaning, cooling, evaporation and the system used for comparison. A single claim such as “up to 90% less” does not describe universally achievable system performance.
10. Getting started by operating level
Learning
A small Kratky or wick system with leafy vegetables; include water analysis, measuring instruments and record-keeping from the outset.
Hobby production
DWC, flood-and-drain or drip system with separately testable circuits, alarms and defined cleaning procedures.
Professional operation
First define the market, crop plan, workflow, hygiene, failure strategy and economic viability; then size the system and automation.
11. Technical sources
- Oklahoma State University Extension: Hydroponics – systems and nutrient-solution management.
- Oklahoma State University Extension: Electrical Conductivity and pH Guide for Hydroponics – source water, pH, EC and measurement practice.
- Cornell University: Controlled Environment Agriculture – technical material on crops, lighting, energy and operations.
- FAO/University of Hawaiʻi: Managing a non-recirculation hydroponic unit – non-circulating lettuce production.
- University of Florida IFAS: Small-scale hydroponic lettuce production – guidance on EC, pH and production.
Application note: Reference ranges and procedures must always be adapted to the crop, cultivar, growth stage, source water, climate, system technology, measurement method, occupational safety, food safety and applicable legislation.