Leafy greens remain among the most profitable crops for UK glasshouse growers, particularly when using soilless systems that offer precise control over growing conditions. Two hydroponic methods dominate commercial and small-holding operations: nutrient film technique (NFT) and deep water culture (DWC). Understanding the distinctions between these systems—their operating principles, resource demands, and failure risks—is essential for choosing the right approach for your enterprise.
How NFT and DWC systems work
Nutrient film technique draws its name from its core principle: a thin film of nutrient solution continuously trickles along gently sloping gutters where plants sit at intervals. Roots develop within this flowing channel where they contact both moisture and oxygen, with excess solution recycled via pump back to the storage tank. The system is fundamentally active, requiring uninterrupted power for circulation.
Deep water culture operates differently. Plants float on rafts or platforms suspended in tanks containing 330 litres of oxygenated solution per unit. Rather than constant flow, water movement is ensured through aeration—typically via air stones or diffusers powered by an air pump. Roots remain submerged in the nutrient bath, drawing nutrients directly rather than depending on film flow. This method also requires electrical input, but for aeration rather than continuous circulation.
Temperature and dissolved oxygen: the critical factors
For most leafy greens, the optimum growing temperature falls between 18 and 23°C. However, research on mini Romaine lettuce shows that heating the nutrient solution to a minimum of 22°C during cooler months significantly boosts production efficiency and leaf mass per system area. This temperature control is more straightforward in NFT systems, where solution volume is lower and therefore cheaper to heat. DWC tanks, holding substantially more solution, demand greater energy input to maintain target temperatures and are more vulnerable to thermal lag during cold periods.
Dissolved oxygen presents an equal challenge. Both systems depend on adequate oxygen at the root zone—roots of most plants die in stagnant water. In NFT, the film provides contact with air as solution flows past roots. In DWC, aeration must be reliable and continuous; system failure allows oxygen depletion within hours, risking root death and crop loss. Additionally, warmer solution holds less dissolved oxygen, creating a compound problem when heating DWC tanks during winter months.
Common risks and disease pressure
Temperature fluctuations and oxygen stress create conditions favouring root diseases. Phytophthora cryptogea, an oomycete pathogen, causes severe root rot in hydroponic lettuce and other leafy greens. Infected roots deteriorate rapidly, reducing vigour and yield. Current challenge in UK production is that fungicides approved for application into hydroponic growing solution remain limited, placing greater emphasis on prevention through system design and water management.
NFT’s flowing solution moves pathogens less predictably through the system, localising early infections. DWC’s static tanks allow pathogens to spread throughout the entire volume once introduced, affecting all plants simultaneously. This difference is significant for small holdings, where crop loss is proportionally more damaging.
Power interruption also presents distinct risks. NFT loss of pump circulation stops nutrient delivery within minutes; roots dry out rapidly in the exposed gutter. DWC loss of aeration is equally critical but slightly slower, with oxygen depletion occurring over hours rather than minutes. Both systems require backup power or alarm systems for continuity.
Maintenance and monitoring
NFT systems demand regular checking of trickle lines for blockages—small debris or algae can restrict nutrient delivery to specific plants, creating patches of underperformance. Solution pH and electrical conductivity must be monitored (target pH 5.8–6.2), and complete solution replacement is advisable every two weeks to prevent nutrient imbalance accumulation.
DWC requires less daily attention to flow rates but demands more rigorous aeration monitoring and temperature control. Tank cleanliness is critical; algae growth in standing solution reduces visibility and competes for nutrients. Solution changes are similarly advisable every two weeks.
Both systems benefit from ebb-and-flow approaches as an intermediate option. Ebb-and-flow periodically floods plant containers in substrate (perlite, rockwool) before draining back to storage, combining some passive growing-medium buffering with recirculation efficiency. This method suits growers seeking to balance the simplicity of DWC with the energy efficiency and root protection of partial submersion.
Practical choice for small holdings
Small UK glasshouses—typically 100–500 square metres—rarely justify the expense of complex environmental controls. NFT systems suit premises with reliable electricity and access to mains water; their lower solution volume reduces heating costs, and their modularity allows incremental expansion. DWC works better where larger groups of uniform plants justify the tank investment and where temperature stability is easier to maintain (ground-based glasshouses with earth as thermal mass, or operations with spare capacity for additional tanks as buffers).
Energy costs remain the dominant operating expense. Most vertical farms with intense lighting fail to reach commercial viability due to electricity demand. For glasshouses relying on ambient light, heating solution to 22°C during winter months adds measurably to running costs in both systems, but NFT’s lower volumes make incremental investment more proportional.
Key points
- NFT systems flow nutrient solution constantly past roots; DWC systems suspend roots in oxygenated static solution
- Optimal growing temperature for most leafy greens is 18–23°C, with heating to minimum 22°C improving winter yields
- Both systems demand backup aeration or circulation systems to prevent total crop loss during power failure
- Root diseases such as Phytophthora cryptogea spread throughout DWC tanks but remain more localised in NFT gutters
- NFT suits smaller operations and uneven power availability; DWC suits larger batches with stable electrical supply
Related service: Agricultural research and development