Dialing in Hydroponic Drip Irrigation

Drip irrigation, also termed micro-irrigation, trickle irrigation, or low volume irrigation, is an efficient method of supplying nutrient solution slowly and directly to the root zone.

While we think of modern hydroponic systems using a range of specialty irrigation equipment as high tech, low tech versions of drip irrigation have been in use for crop production for centuries. The earliest drip irrigation systems consisted of unglazed clay pots filled with water and buried in the soil which allowed water to gradually leak out and irrigate surrounding plants.

With the development of accurate plastic molding came the design of drip irrigation system components that allowed further progress with nutrient delivery systems in soilless crops. The development of plastic emitters post World War Two revolutionized drip systems as it created a method for water to flow through passageways inside the emitter, helping to prevent clogging and slow the flow of nutrient solution to create a slow drip release pattern.

Hydroponic Drip Irrigation

Drip irrigation systems for hydroponics come in a variety of forms. The oldest and most basic are porous pipes that may be sub-surface or surface-positioned in media beds. While these are easy to install, they can have issues with uniformity of nutrient solution distribution, are prone to clogging with salts, sediments, and other material, and need to be installed on flat ground.

Another inexpensive method of drip irrigation is the use of drip tape that is made from polyethylene of varying thickness and sold flat on reels. Drip tape has holes, slits, or emitters at spacing ranging from six to 24 inches pre-installed in the product through which nutrient solution is released directly into the substrate. Drip tape technology these days is much more advanced than in the past with designs that help prevent clogged filters and internal emitters that improve reliability and the usable lifespan of the system.

While drip tape is more widely used in soil applications than hydroponics, it can be adapted for use in media bed systems. The main issue with drip tape is that it is difficult to control exactly where nutrient is released since the nutrient distribution points are pre-fixed on the tape, so some plants may receive more solution application than others. The inexpensive nature of thin-walled drip tape, however, means this can be replaced with each successive crop and avoids much of the requirement to clean and flush irrigation systems.

Read also: Maintenance Tips for Drip Irrigation Systems

More advanced and widely used flexible drip systems incorporate the use of a wide range of specially designed emitters that operate at low pressure and allow adjustment of nutrient flow rates. The drip irrigation system typically consists of either a pressurized water supply with nutrient injectors or a central nutrient reservoirwith a pump to provide low pressure to the system.

Filtration is also commonly included to remove sediment and other material that may block components and emitters in recirculating drip systems. A filter may also be included on the nutrient return system. Drip systems then feed nutrient solution through a main irrigation line or ring out to the cropping area that feeds smaller diameter lateral pipes carrying the solution along the rows of plants.

Small diameter drip tubing (also called microtubing or spaghetti tubing) may then be installed into the length of lateral lines. These each have a dripper or emitter fixed to the end; this is then staked around the base of each plant to hold the dipper in position. These types of systems give maximum flexibility with placement of the emitter allowing for differences in plant spacing to be easily accommodated.

Drippers or Emitters

Drippers or emitters control the flow of nutrient to the plant and come in a wide range of different options and can be a little confusing for inexperienced growers. First, drippers are sized by the volume of nutrient solution they deliver, with most hydroponic drippers being one-half to two gallons per hour. Drippers are then further divided into pressure compensating and non-pressure compensating.

Pressure compensating drippers are more commonly used in large scale commercial hydroponic systems as they are designed to discharge nutrient solution at a very uniform rate under a wide range of system pressures. They deliver the same flow rate irrespective of pressure. These types of emitters are particularly useful in hydroponic systems as all drip emitters will start dispensing solution at the same time and prevent drainage of the solution after the irrigation has been switched off. Pressure-compensating emitters often incorporate a turbulent flow design that helps keep sediment and other particles in motion to help reduce clogging.

One of the issues with pressure compensating drippers is that they don’t perform well on very low pressures, such as with gravity fed systems.

Non-pressure compensating drippers are the second type of emitter that also has applications for hydroponic systems. These emitters consist of two parts, a central body that is installed into the microtubing, and a screw on top that can be used to adjust the flow of nutrient. By winding the top further down onto the body of the emitter the flow of nutrient can be slowed or increased by winding it up. This allows for emitters in the same system, under the same pressure, to deliver different rates of nutrient flow depending on what is required by individual plants.

For smaller hydroponic systems, which often have plants at different stages of development and sizes present at the same time, these are great for making sure larger plants get a higher flow rate than recently planting seedlings. The ability to remove the top of the emitter and see the inside also means that any blockages can be easily cleared out.

How to Run and Monitor Drip Irrigation

Running a drip irrigation system is relatively straight forward, but since plant nutrient requirements change as they grow and develop, some monitoring is always required. A timer is used to control the frequency and amount of irrigation flowing through the drip system and this needs to be adjusted for factors such as plant size, growing conditions, and substrate used.

Drip irrigation systems installed into highly moisture-retentive substrate such as coconut fiber often need less frequent irrigation than those on free-draining mediums such as expanded clay aggregates or chunky perlite. As plants mature, they require longer irrigations to fully flush nutrients through the substrate and replenish lost moisture levels.

Read also: Irrigation: You Want Wet Plants, Not Soaked Plants

The easiest way to determine how long to run a drip irrigation system at each irrigation is to time how long it takes for nutrient solution to be seen draining from the base of the substrate of each plant after switching it on. This becomes the set time required at each successive irrigation and frequently changes as the plants grow or as conditions become warmer or cooler.

Issues and Maintenance

The main issue encountered with drip irrigation is the clogging of the emitters with salts, sediments, or other material resulting in uneven flow rates. High-quality water and pre-filtration can assist with some water supplies particularly where sediment, sand, or other organic matter might be present.

Iron minerals in some water supplies are also a major contributor to blockages of irrigation equipment and are best removed before using to make up nutrient solutions. Drippers fully exposed to direct light can result in salt deposits accumulating and algae can also grow around emitter outlets causing blockages.

In recirculating hydroponic systems where the solution drainage is redirected back to the nutrient tank for further irrigation, particles of growing substrate, pieces of root system, and other organic material can all result in emitter blockages unless suitably sized filters are installed on the system. To avoid these issues resulting in plant growth problems, drippers should be regularly monitored while the irrigation is on to ensure all are working correctly.

Blockages can often be cleared by tapping the dipper to loosen any sediment, and accumulated salts can be removed by submerging the dripper in hot water for a few minutes to dissolve any deposits. Stubbornly clogged emitters may need to be replaced so keeping a few spares on hand is always advisable. Between crops, or at least once a year, drip irrigation systems can be cleaned with acid to remove salt deposits, algae, and bacteria.

Drip irrigation systems, if well designed and maintained, are a highly efficient nutrient delivery method for hydroponic substrate systems. Even those with existing systems often benefit from trialing different types and styles of emitters to determine which is the most reliable and easy to maintain in their hydroponic garden.