Greenhouse Sprinklers, Misters and Cooling Nozzles: A Complete Guide

Introduction

Greenhouses and polytunnels create a controlled growing environment, but that control comes with responsibility. Without the natural cooling effect of wind and rain, temperatures can rise rapidly on sunny days, humidity can drop to damaging levels, and crops can suffer heat stress even in the UK's relatively mild climate.

The right overhead irrigation and misting system does more than just water your plants — it regulates temperature, maintains humidity, supports propagation, and can even be used for frost protection. This guide covers the main types of sprinklers, misters, and cooling nozzles used in greenhouse and polytunnel environments.

Understanding the Different Applications

Before selecting equipment, it is important to understand what you are trying to achieve. Greenhouse overhead systems typically serve one or more of the following purposes:

• Crop irrigation — delivering water directly to plants or growing media
• Humidity control — maintaining relative humidity levels to reduce plant stress and prevent tip burn in leafy crops
• Evaporative cooling — reducing air temperature through fine misting, particularly important in summer
• Propagation — maintaining a humid microclimate around cuttings and seedlings to prevent wilting before roots establish
• Frost protection — applying water to create a thin ice layer that protects buds and young growth from frost damage

Micro Sprinklers

Micro sprinklers are the workhorses of greenhouse overhead irrigation. They deliver water in a rotating or fixed spray pattern, covering a defined radius at relatively low flow rates (typically 30 to 150 litres per hour).

• Available in full-circle, half-circle, and quarter-circle patterns to suit different bed layouts
• Interchangeable nozzles allow you to adjust flow rate and coverage radius
• Can be mounted on stakes, hung from overhead wires, or fitted to risers above the crop canopy
• Operating pressure typically 1 to 2.5 bar

Browse our range of NDJ Micro Sprinklers for a comprehensive selection of heads, nozzles, and accessories.

Misting Systems

Misting systems produce much finer droplets than standard sprinklers — typically in the 50 to 100 micron range. At this droplet size, water evaporates rapidly in the air rather than falling directly onto the crop, making misting systems highly effective for humidity control and evaporative cooling.

Low-Pressure Misting

Operates at standard irrigation pressures (2 to 4 bar) and produces a fine mist suitable for humidity maintenance and propagation. Best for propagation houses and humidity maintenance in vegetable and flower production.

High-Pressure Misting

Operates at 40 to 70 bar using a dedicated high-pressure pump and specialised nozzles. Produces extremely fine droplets that evaporate almost instantly, providing highly effective evaporative cooling without wetting the crop. Can reduce air temperature by 5 to 10 degrees Celsius. Best for summer cooling in tomato, cucumber, and pepper houses, and high-value crops where heat stress is a significant risk.

Cooling Nozzles

Cooling nozzles are designed specifically for evaporative cooling applications. They produce a fine, fan-shaped or conical spray pattern optimised for maximum surface area and rapid evaporation. Our range of Super Fogger – IrriSmart includes specialist cooling and misting nozzles suitable for a wide range of greenhouse applications.

When selecting cooling nozzles, consider flow rate, spray angle, droplet size, material, and spacing. Stainless steel or ceramic nozzles offer better longevity than plastic in high-pressure applications. Nozzles are typically spaced 1.5 to 3m apart depending on greenhouse width and height.

System Design Considerations

Mounting Height

Overhead systems should be mounted high enough to allow droplets to partially evaporate before reaching the crop canopy — typically 2 to 3m above the growing surface for misting systems. Micro sprinklers for direct irrigation can be mounted lower, at or just above canopy height.

Zoning and Automation

Divide your greenhouse into zones based on crop type, growth stage, and orientation. South-facing sections will heat up faster and may need more frequent cooling cycles. A humidity sensor or thermostat-triggered controller can activate misting cycles automatically when temperature or humidity thresholds are reached, without requiring constant operator attention.

Filtration

Fine misting nozzles are extremely sensitive to blockage. High-quality filtration is essential, with 200 mesh (75 micron) or finer recommended for misting systems. Our Amiad Filters range includes fine filtration options suitable for misting applications.

Water Quality

Hard water causes limescale deposits that can block nozzles and reduce performance over time. If your water supply is hard (above 200 ppm calcium carbonate), consider water softening or acidification to prevent scale build-up, particularly in high-pressure misting systems.

Outdoor Sprinklers for Nursery Areas

For outdoor nursery areas, sports turf, and open-ground production adjacent to your greenhouse, our range of Outdoor Sprinklers covers impact sprinklers, pop-up heads, and rotary sprinklers suitable for larger coverage areas.

Conclusion

Choosing the right overhead system for your greenhouse or polytunnel comes down to understanding your primary goal and matching the right equipment to that need. With 20+ years of experience supplying irrigation solutions to UK growers, the IrriSmart team can help you design a system that keeps your crops healthy and productive through every season.

Browse our full range of micro sprinklers, cooling nozzles, and outdoor sprinklers online, or get in touch for expert advice.