A Tale of Two Hydro Systems: Drip Irrigation & Ebb and Flow
In his first article comparing popular hydroponic grow systems, Frank Rauscher analyzes the similarities and differences between drip irrigation and ebb and flow methods of growing. Both systems use pots and are simple and economical, making them both ideal for commercial applications, but is one better than the other? Let’s find out!
The two popular types of watering systems I am about to compare in this article are ebb and flow, and drip irrigation. Deep water culture (DWC), recirculating deep water culture, and nutrient film technique (NFT) are other commonly used systems, yet substantially different from these two—they will be compared in future articles. Let’s get on with the comparison at hand, starting with some simple definitions:
Ebb and Flow
Ebb and flow is a form of hydroponics that is known for its simplicity, reliability of operation, and low initial investment cost. In this system, pots are filled with an inert medium that is usually not soil but much more porous, yet capable of anchoring the roots and functioning as a temporary reserve of water and solvent mineral nutrients. The hydroponic solution alternately floods the system and is allowed to ebb away.
Drip irrigation hydroponic systems are also simple and economical. True drip irrigation utilizes drip emitters that actually drip water rather than spray or run it. Drip irrigation for outdoor crops was developed in Israel to maximize the amount of scarce water being used to grow outdoor crops. Drip avoids loss of water through reduced evaporation, leaching, and runoff in the outdoors. In hydroponics, the leaching action really doesn’t come into play unless the system is allowed to run far past saturation.
When new growers are considering which type of grow system they might want to use, there are a few important aspects they need to look at:
- Yield potentials
- Overall efficiency
- Operating and nutrient costs
- Set-up complexity and costs
- Operational complications
- Likelihood of pest and disease problems
- Maintenance and material replacement costs
Yields: Root & System Size
As will be discussed later, if a drip system fails to evenly distribute moisture throughout the root system, ebb and flow, which naturally does this, will out-produce a drip system. If there are sufficient and properly spaced emitters in the drip system, there will really not be a difference between these two systems when it comes to yields. Proper watering frequency throughout the maturity of the crop’s cycle, proper nutrients, and adequate lighting levels will have the most impact on yields.
To compare root system differences between these hydroponic systems, we need to consider how each system affects root growth, each system’s limit for root growth capacity, and aspects that may damage root growth and vigor. Larger and healthier root systems produce greater yields. Smaller pots restrict the ultimate size a root system can grow. However, either of these systems can utilize larger pots. The table size for the ebb and flow systems can be an issue for a large number of large pots.
With drip, the pot size and quantity of plants is basically limited by the size of the growroom—not the grow table—giving drip systems the advantage in size capacity. Another factor for producing larger root systems is the amount of foliage growing for the plant, and hence photosynthesis. Sufficient space allows for more foliage, which puts greater demand on the plants to produce larger roots. Once the plant is ready for the bloom phase of growth, and the roots are fully developed, some of this foliage can be pruned away.
As crop yield and space utilized go hand-in-hand with the size of the root system for each plant, the access to an abundance of photosynthetically active radiation (PAR) provided is also very important. Available light relates to the watering system in that the set-up of the system allows for sufficient spacing. Because it can be easier to provide more growing area with drip than with ebb and flow, drip systems have an edge in this category.
Efficiency: Nutrients & Energy
Electricity use is usually a big consideration for hydroponic growers. The energy used to provide light energy for the plants is by far the greatest factor, while the energy used for watering is far less. In regards to this aspect, the only extra energy used by an ebb and flow system is the water that is pumped up to the tray that fills the spaces between the pots, and the amount of cycles the pump needs to run. If the drip system provides adequate distribution and even water to each plant, the energy for watering the pots is equal for each system.
Only the energy for watering the spaces and the number of cycles required is different. Usually, a 40-50W pump is plenty enough power for about 10 seven-gallon plants. At $0.22 per kilowatt hour and a 40-minute run time every day (more often than needed in many situations) this would amount to around $0.22 per month for drip and $0.66 for ebb and flow. This is not significant.
The fact that most ebb and flow systems require more cycles and an aeration pump running to keep the solution from becoming anaerobic and toxic will add a small amount to your electrical and set-up costs.
Nutrient expenses can be significant when the nutrient reservoir needs to be drained and reestablished every two to four weeks due to recirculation. For a 12-week maturity crop this means the nutrient expense can be anywhere from three to six times as high with ebb and flow as with drip.
The grow media used in each system has a big impact on many decisions that need to be made regarding both of these systems. Aspects such as initial cost, ongoing cost, the recirculation effect on water quality, and watering and nutrient scheduling for the various grow media all come into play. Make sure you choose the right grow media for your operation and then design the set-up to match that. There is a ton of information on grow media on my reference webpage, a link to which can be found at the end of this article.
In both ebb and flow and drip, the plants are usually growing in pots. Because optimizing yield will require larger and healthier roots, a drip system set-up must utilize enough emitters to spread the water around at the surface of the pot to thoroughly and evenly moisten the entire surface area in the pot so as to have uniformly moist grow media in the pot. The faster the grow media drains, the more emitters the drip system will need.
With ebb and flow, the total grow media volume is immersed in the nutrient/water solution each time the plants are watered, so the aspect of thorough even distribution of water is easier to accomplish with the ebb and flow than with typical, two-emitter drip systems. In a drip system, there are some special considerations to make:
- Drip irrigation with few emitters – At the point where water is applied to the soil or grow media and depending on the perk rate of that media, the moisture area for the soil will likely look somewhat like Fig. 1. A slower application rate and/or a dense grow media like soil or coco will also spread the pattern out and apply a more thorough application of water.
- Drip irrigation with many emitters – The more locations for water application, the better (Fig. 2). By adding to the number of drip emitters for each grow pot, the distribution of water in the pot is improved substantially. Yield is then correspondingly optimized. Modular drip systems simplify set up significantly. Connections are easily made and emitter placement is pre-set in the design itself.
Operational Complications: Maintenance & Diseases
One complication for any system a gardener might be contemplating is component failure. How serious are the various failures for the two different systems? What can be done during set up to reduce the likelihood or seriousness of those failures?
The failure of an ebb and flow system to drain can be very costly if protections are not included in the design and set up. There are sensor controllers available that can recognize when a failure has occurred and prevent the pump from continuing or activating. Running too long and overflowing the grow table needs to be prevented as well.
If a drip system is allowed to run far past soil or grow media saturation, water and nutrient is wasted and potential flooding damage can occur if the system is not designed well or scheduled properly. Regardless of the system, the failure of the pump to supply water will lead initially to plant stress, desiccation, and plant death, depending on how long the failure lasts and the type of plant being grown.
Plant maintenance can be easy or difficult depending on how each system is set-up. For example, how easy is it to remove a single plant from the set-up in order to prune, examine, or spray? Can the plant be removed permanently with ease, or are there a number of connections that will have to be cut and then others re-attached? With ebb and flow, as long as the tray or table isn’t too wide to allow reaching for plant access, maintenance is not an issue.
Just pick the plant up and move it, then return it or not. With non-modular drip systems, removing one or two plants can be enough of a hassle to discourage you from doing the maintenance (at least temporarily) because of the connections issue. The drip systems that utilize special modular connections that make disconnect and re-connect easy make this aspect nearly as easy as with ebb and flow. Ebb and flow has the edge versus the more typical non-modular drip system.
The difference in root disease risk is substantial between these two systems. With ebb and flow, the reservoir water is recycled and mixed between each plant, so if one plant gets phytophthera (root rot) they are all likely to get it. Chilling the water for an ebb and flow system is often recommended to minimize bacterial and fungal growth. With drip systems there is no recycling or mixing. In the case of both systems, the water reservoir should be cleaned routinely in order to keep diseases at a minimum.
The verdict? There isn’t a clear winner. When it comes to choosing the best hydroponic system on the market, make sure to consider all the parameters that will affect your success before you leave the planning stage and begin building. Enjoy!