Water is central to hydroponics—which derives from Greek “hydro,” meaning “water,” and “ponos,” meaning “work”—and indeed to all plant cultivation. As we explained in our previous blog post on choosing a hydroponic system, there are several irrigation systems available to growers. But irrigation can do more than supply water; when paired with nutrient dosing units, they deliver water enriched with essential nutrients.
In this blog post, we’ll discuss the benefits of irrigation, the components growers need, how to schedule irrigation and best practices for getting the most from the system.
Benefits of irrigation
Irrigation systems allow growers to deliver water accurately and consistently, promoting uniformly grown, equally lush and prolific plants. If paired with a nutrient dosing unit, they compose a fertigation system that seamlessly manages both hydration and nutrient supply.
These systems can reduce manual labor, especially in dense setups like Sea of Green, where manual watering is often impractical. Automation frees growers to focus their time and efforts on other tasks, while recirculating designs such as drip, ebb-and-flow and NFT[1] reduce water waste by collecting and reusing runoff.
Designing the irrigation system
Because cannabis is prone to diseases like leaf spot and downy mildew when its foliage stays wet,[2] irrigation should target only the roots. All hydroponic systems achieve this, and drip irrigation can be used both hydroponically and in soil-grown cannabis.
Every irrigation system needs a water source, either a reservoir, tank, municipal supply or well; see our previous blog posts on selecting the right water source and ensuring water quality. From there, growers will need to know their grow-space size, plant density and proximity to the water source to determine the most efficient irrigation system layout, as well as the amount and length of materials needed.
Common irrigation components include:
- Pipes and fittings move water from the source across the grow area and, in recirculating systems, back to the reservoir.
- Filtration units remove debris, particulates and organic matter to prevent clogs. Screen filters use mesh. Disc filters use stacked grooves. For the purest water, use reverse osmosis.
- Nutrient dosing unit injects fertilizers into the irrigation water automatically.
- Moisture sensors monitor water content and help automate schedules. For hydroponic drip, use a sensor suited to the growing media, rather than one designed for soil.
- Timers automate irrigation.
- Valves control the flow of water to specific zones or plant sections.
Common irrigation components include:
- Pipes and fittings move water from the source across the grow area and, in recirculating systems, back to the reservoir.
- Filtration units remove debris, particulates and organic matter to prevent clogs. Screen filters use mesh. Disc filters use stacked grooves. For the purest water, use reverse osmosis.
- Nutrient dosing unit injects fertilizers into the irrigation water automatically.
- Moisture sensors monitor water content and help automate schedules. For hydroponic drip, use a sensor suited to the growing media, rather than one designed for soil.
- Timers automate irrigation.
- Valves control the flow of water to specific zones or plant sections.
Depending on the irrigation system, other materials might include:
- Dripper lines carry water from the pipes to the drippers or emitters in drip irrigation. Some regulate flow.
- Drippers or emitters control water delivery in drip systems. Choose based on flow rate and volume.
- Stakes hold the dripper lines and emitters in place. Some include built-in emitters. Avoid stakes that spray foliage.
- Pressure gauges monitor water pressure and usage.
- Pressure regulators and pumps maintain consistent water pressure. Regulators lower excess pressure. Pumps boost low pressure and move water in recirculating systems.
- Flush valve end cap flushes drip lines before and after irrigation to prevent salt buildup from fertilizers.[3] In hydroponics, this is needed only for non-circulating systems.
- Grow channels hold the plants and flowing water in NFT systems.
- Air pumps or stones provide oxygen in DWC[4]
Always use high-quality, durable, flexible materials that withstand pressure and environmental stresses. Keep detailed digital records of all components for quick identification and replacement if needed.
Irrigation scheduling
For systems like drip or ebb-and-flow, growers must set irrigation intervals. By contrast, NFT and DWC provide constant root-zone access to the nutrient solution but still require monitoring.
Scheduling drip irrigation
Drip irrigation delivers precise amounts of water and nutrients to the root zone. To decide how often and how long to irrigate, growers first need to know how much water the plants need.
A safe rule: 0.5‒1 liter of water per square foot of canopy, depending on light, temperature, VPD, growth stage and CO₂. For example, a 100-square-foot canopy needs about 100 liters per day. Unless the crop is under intense light, high temperatures and significant carbon dioxide, plants will use less than this maximum, guaranteeing they have enough.[5]
Another way to determine water volume is to target a 30% leaching fraction, the portion of irrigation water that exceeds what the roots and substrate can hold and drains out, flushing fertilizer salts from the root zone.[6]
Growers can calculate this by measuring how much water it takes before runoff appears at the container bottom, calculating 10–30% of that amount, then adding it back. For example, if 150 mL produces first drip, 10–30% of 150 mL is 15–45 mL, so irrigate 165–195 mL per plant or container.[7]
Once growers have determined the water volume, they then need to calculate how long each irrigation should run. Use the following equation:
Irrigation duration = total water volume ÷ (emitter flow rate × number of emitters)
Growers can calculate this by measuring how much water it takes before runoff appears at the container bottom, calculating 10–30% of that amount, then adding it back. For example, if 150 mL produces first drip, 10–30% of 150 mL is 15–45 mL, so irrigate 165–195 mL per plant or container.[7]
Once growers have determined the water volume, they then need to calculate how long each irrigation should run. Use the following equation:
Irrigation duration = total water volume ÷ (emitter flow rate × number of emitters)
For example, in a 100-square-foot space applying 1 liter per square foot, the target is 100 liters per day. With two plants per square foot, each with an emitter flowing at 0.5 gallon (or roughly 1.9 liters) per hour, 200 emitters provide 380 liters per hour. Dividing 100 by 380 gives 0.26 hours, or about 16 minutes of irrigation.
Scheduling ebb-and-flow irrigation
Unlike drip irrigation, which delivers exact amounts of water and nutrients to the roots, ebb-and-flow, also called flood-and-drain, floods the root zone periodically and lets the water drain away. Each irrigation should flood to just below 1 inch from the top of the growing media and drain once it’s fully soaked. Irrigate again before the media begins to dry and contract.[8]
Best practices for irrigation
Once the system is set up, verify that it’s working properly. Visually assess components and plants for uniform growth and moisture and look for leaks. Where possible, check the actual flow rate and working pressure. Calibrate sensors as recommended by the manufacturer to ensure accurate automation and data collection.
Timers can automate irrigation. An automated grow-room system can adjust the frequency and volume of irrigation based on moisture-sensor feedback and digitally log irrigation and moisture data for future reference. However, always check the system and plants manually for signs of over- and under-watering and adjust as needed.
Although automation lets growers “set it and forget it,” it’s imperative to be proactive. Regular monitoring and maintenance prevent problems such as leaks and clogs, which waste resources and disrupt uniform watering.
Incorporate irrigation cleaning into your SOP. Clean filters regularly and flush the system periodically to remove fertilizer salts that can clog emitters, reduce flow and block nutrient uptake. Follow the manufacturer’s manual for specific guidelines.
Finally, avoid watering in the morning or evening, when humidity is typically highest, to reduce the risk of raising humidity further. Time irrigations with plant transpiration, beginning shortly after lights-on and avoiding irrigation during dark periods.
An efficient irrigation system saves time, labor, water and fertilizer while giving plants exactly what they need for high yields and quality buds. Designed and maintained well, it pays off in every harvest.
Emerald Harvest Team
[1] Nutrient film technique
[2] Korus, Kevin, Wael Elwakil, Nicholas Dufault, and Zachard Eldred. 2024. “Field Guide to Hemp (Cannabis sativa) Diseases.” University of Florida, IFAS Extension. https://doi.org/10.32473/edis-pp379-2024.
[3] GROWLAB. 2021. “Simple DIY Drip Irrigation Setup for Any Grow.” Posted August 13. YouTube, 7 min., 3 sec. https://www.youtube.com/watch?v=U5UecquUKHc.
[4] Deep water culture
[5] Douglas, Ryan. 2022. “Ways to Calculate Water Use and Transpiration Rates for Indoor Cannabis Cultivation.” Greenhouse Grower, January 13. https://www.greenhousegrower.com/production/how-to-calculate-water-use-and-transpiration-rates-for-indoor-cannabis-cultivation/.
[6] Eddy, Robert. 2021. “Are You Well Versed in Hydroponics?” Cannabis Business Times, March 2. https://www.cannabisbusinesstimes.com/containers-growing-media/hydroponic-cannabis-cultivation/article/15690588/are-you-well-versed-in-hydroponics.
[7] Ibid.
[8] Nelson II, Mykl, Gail Langellotto, and Lloyd Nackley. 2025. “Hydro Hints: Ebb and Flow.” Oregon State University Extension Service. Accessed September 18, 2025. https://extension.oregonstate.edu/catalog/pub/em-9458-hydro-hints-ebb-flow
