Water Conservation Strategies for Greenhouses

By Jane Marsh

Greenhouses deliver a highly controlled environment where crops and other plants can be grown year-round. However, these mechanisms consume ample water, forcing growers to reevaluate their approach to irrigation and sourcing and implement alternative methods. After all, if greenhouses are to contribute to a sustainable food supply, professionals must adopt efficient water conservation strategies. 

How Much Water Does a Greenhouse Use?

Greenhouse crops require large amounts of continuous irrigation. However, the type of plants, temperature specifications, and atmospheric conditions ultimately determine how much they need to grow. Growers must consider that producing dry organic matter requires 300 to 500 pounds of water, 99% of which is absorbed into the atmosphere. 

Growers must provide just the right amount at the right time. Otherwise, too much water infiltrates fertilizers and lessens aeration, while too little stunts crop growth. Irrigation should typically raise the soil’s water content to 70%-80%. Plants will not need much watering if they’re shaded or it’s cloudy outside.

Water Conservation Methods for Greenhouses

Fortunately, growers can integrate numerous water-conserving methods — a combination of holistic approaches and the utilization of new technologies — to decrease resource consumption.

• Drip Irrigation

Some greenhouses use overhead sprinklers, which often miss the pots and inadequately irrigate plants with high water requirements. Drip systems are far more efficient in terms of water conservation. These irrigators eliminate runoff with precision watering of the plant roots. 

Growers can use a tensiometer in the soil to measure moisture content. This tool connects to a computer program and turns off the system automatically when appropriate moisture levels are reached.

• Rainwater Harvesting

Greenhouse facilities with room for storage infrastructure can conserve water with a rainwater harvesting mechanism. Because precipitation trends vary depending on the location and climate, harvesting rain may be best suited as a supplemental approach.

The tanks used to store the water should be U.S. Food and Drug Administration-approved to prevent bacterial growth. These mechanisms should also have a control system and pump to move the water throughout the greenhouse.

This method collects water from rooftops and gutters during storms, delivering an alternative source to groundwater and surface water for later use. Typical applications in a greenhouse setting could include irrigation, cleaning, pond and fountain filling, and flushing. 

• Grey Water Recycling

Grey water is recycled from a bathroom sink, shower, laundry machine, or other household application. While it doesn’t come into contact with toilet feces, it can still contain traces of cleaning solutions, grease, hair, dirt, and other household substances. 

Using grey water helps decrease water in sewers and septic systems, keeping pollutants out of natural sources. Growers can use it to irrigate fruit trees and ornamental plants but should avoid having it touch the edible parts.

Professionals should consider the sodium and boron concentrations in grey water if taking this approach. Sodium can reduce soil’s moisture capacity over months of buildup, while boron and chlorine from laundry products can burn the plant.

• Soil Moisture Sensors

Greenhouse professionals may employ soil moisture sensors to measure and manage water consumption in real-time. Growers can then use the insights to make more informed decisions and adjust irrigation amounts accordingly. The tool’s other benefits include precision irrigation, maintaining plant health, and reduced labor costs.

According to researchers at Clemson University, soil moisture sensors increase farmers’ net incomes by 19.42% on average or $202.28 per acre.

One study showed that 80% of farmers are willing to purchase soil moisture tools, but only 4% currently use them. Although this advanced technology is an investment, cost isn’t always the determining factor. Calibrating the sensors for accurate readings, maintenance and knowledge barriers are more of a challenge.

Sustainable Sourcing for Greenhouse Water Supplies

Greenhouse professionals should regard sustainable water sources as highly as irrigation tools and methods. For instance, surface water provides adequate water through a reservoir. However, growers must also be aware of drought and pollution. 

Aeration systems can help with the latter by stabilizing oxygen levels in a larger water body and providing continuous movement and ventilation. This process cuts off oxygen to bacteria, resulting in their inability to break down organic matter. Otherwise, the matter rots to muck and forms harmful algae.

Retention ponds and drilled wells are other potential water sources for greenhouse landscaping. The ponds collect pooling water from irrigation and stormwater runoff for later use, similar to rainwater harvesting with storage infrastructure. However, growers must implement robust pest management, as standing water attracts mosquitoes with vector-borne diseases.

Drilled wells are another option, pumping pollution-free groundwater. However, there are caveats, as widespread pumping could deplete fragile aquifers, cause poor water quality, and induce land subsidence — when the soil compacts and drops.

The most serious implication of drilled wells is the lowering of the water table, in which too much groundwater is drawn. This leads to a dried well and lower levels in lakes and rivers. 

Although municipal water is expensive for large-scale use, it is perhaps the most reliable source for consistent irrigation. Greenhouses also benefit from consistent water pressure and quality. Integrating sustainable tools and methods for conservation into municipal sourcing could be a viable solution for greenhouse growers.

Additional Tips for Water-Conserving Greenhouse Irrigation

Regardless of the water conservation strategy employed in greenhouse landscaping, growers can make other changes to save resources. Helpful reminders for reducing water consumption include:

• Grouping plants with similar watering requirements to optimize irrigation.
• Irrigating with 10%-15% more than the container capacity — this should have adequate drainage — and using a collection mat to divert excess water to a retainment pond or other plants.
• Generating a water management plan with clear guidelines for consumption, monitoring, and conservation techniques.
• Properly insulating the greenhouse to avoid water loss by evaporation.
• Testing the soil regularly to ensure sufficient nutrient levels and moisture retention.

Water Conservation Is a Foundation of Sustainable Greenhouse Landscaping

Growers shouldn’t overlook water consumption in their greenhouse landscaping practices, as this is one of the Earth’s most precious resources. Conserving it with alternative sources and technologies will improve the industry’s sustainability, ensuring viable, long-term crop yields and a sufficient water supply for a growing population.

Article by Jane Marsh

Jane works as an environmental and energy writer. She is also the founder and editor-in-chief of Environment.co