Second to deep water culture, ebb and flow is another hydroponics system we use for crop production. We grow in 400 square feet of ebb and flow beds, split into 9 different systems. With multiple systems, we are able to tailor nutrients on a system-by-system basis according to the crop in the respective beds.

These systems have proven highly versatile for a wide variety of crops, including root crops (radishes and carrots), leafy greens, herbs, and fruiting crops. Where DWC is good for quick, economical turnaround of single-harvest crops, the growing media in ebb and flow beds allows for better root structure and support of longer-term, multi-harvest crops.

How Does Ebb and Flow Work?

In an ebb and flow system, plants are rooted into a bed filled with a soilless growing media (most often expanded clay pellets or similar product). Nutrient-rich water is pumped into the bed to fill it to a set level (2-3 inches below the top of the media), and then the bed drains entirely. During the drain cycle, fresh air is pulled down to the roots through the growing media, providing oxygen to the roots.

There are several ways to configure the fill and drain cycles for these systems. In our case, we have pumps running continuously to fill the beds, and each bed has a bell siphon. When the water reaches a depth controlled by the bell siphon, it begins siphoning/draining from the bed back to a holding reservoir. We can control the water depth by adjusting the siphon, and control the cycle timing by adjusting the flow rate of water into the bed.

System Versatility and Resiliency

As noted above, these systems are highly versatile. Nearly anything we’ve planted in them has done exceedingly well. Most crops we propagate in grow plugs and then transplant into the ebb and flow systems to get exact plant spacing, but other crops with a high density (e.g. spinach and radishes) can be direct seeded. After a week or two of top-watering with a hose to promote germination and plant establishment, even direct-seeded crops are established enough to thrive off the normal fill and drain cycle.

These systems also allow for multiple crops to increase production density. For example, once kale plants are established it’s easy to plant shorter or smaller crops between them. When trying this, you do have to consider things like nutrient compatibility between crops and pest management, but it’s a unique opportunity not available with other hydroponic systems.

Additionally, because the root zone is not constantly saturated and receives a steady supply of oxygen, these systems are highly effective for cloning plants. In fact, the majority of the tomato plants we have are clones which we cut off the mother plants, planted in the ebb and flows until they had healthy root systems, then transplanted into soil containers.

Lastly, ebb and flow systems and DWC systems are more resilient to power interruptions than NFT systems. With ebb and flow or DWC, if there is a power outage the plants are at least still in water (or relatively saturated growing media); whereas with NFT (especially vertical NFT), when the power goes out the root zone begins to dry out very quickly.