Ebb and Flow - Drawbacks To E&F Systems

Drawbacks To E&F Systems

Ebb and flow systems are flexible, with few practical drawbacks. Though typically known for compact cultivation of plants having smaller stature, it has been used for growing large plants, using buckets ranging in size from 1 gallon to 5 gallons, making use of high-volume pumps such as those in large aquariums, decorative fountains and koi ponds.

There are facets to these systems that present some labor investment in large-scale applications. These are primarily management of media between uses, such as washing and sterilization. This can be done by dumping into the tray and filling with a sterilizing solution such as hydrogen peroxide or chlorine solution, temporarily plugging the drain, with hand removal of root fragments. Larger containers require transferring the media to a suitable surface after sterilization to permit removal of leftover plant material.

A second drawback is that the roots tend to grow together, meaning removal of harvested or damaged plants can be somewhat problematic in plants having well-developed root systems. Commercial crops harvested at one time are somewhat immune to concerns related to that aspect of the system, but in the event of pathogenic invasion the problem can quickly spread, as all the roots share the same flood source.

Also, most ebb and flow systems use a recycling reservoir to flood the table. Over a period of time the pH of the nutrient solution may fluctuate to a range which is unhealthy for the plant. If the pH is not corrected, various problems may occur, including but not limited to poor nutrient absorption and leaf cannibalization. As the name implies, leaf cannibalization occurs as the plant takes nutrients from one part of the plant and uses those nutrients in a different part of the plant. Leaf cannibalization appears as yellow or brown spots on leafs.

During Flower pH rises quite a bit each day. It is best to adjust first thing and last thing each day. Also, during Flower nutrients and water absorption increases, while root exudate gets carried back to the reservoir. This causes ppms to increase significantly. Proper control requires routine checking and replacing with fresh nutrients ~ 5 days to avoid toxicity.

Since the plant(s) is being fed several times a day, lower ppm nutrients (600–800) are sufficient. Pushing with higher ppms can cause the plant to burn up from the inside, especially when significant water evaporation/usage causes the remaining nutrient concentration to increase beyond 1500 ppms.

Choosing a medium like lava rock is ideal for flood and drain in that it drains quickly, and due to its rough texture, it traps small amounts of oxygen and nutrients which keeps the root zone moist between feedings. Also, because it drains quickly, the number of feedings can be increased to roughly every 45–60 minutes during lights on, producing explosive growth. Should the grower opt for this method, the nutrient ppm should be kept below 800, better still 600.

Poor drainage, or incomplete drainage, may cause a condition wherein dense roots are exposed to stagnant water which is trapped by the root mass. Root rot and fungal growth are the most common result of stagnant water. Some E&F systems are not as immune to root rot as a well-designed system would be. In tables where plants are larger than optimal for the system, this can create the need for modifications such as screens or beds of medium-sized gravel to prevent standing water. Tilting the tray is one way to achieve better drain characteristics. In bucket E&F this problem can be dealt with in a similar manner, ensuring good drainage through using medium of adequate size and ensuring that drainage of the container between flood cycles is complete.

Hydrogen peroxide is also added to nutrient solutions when there is suspicion that the anaerobic pythium root rot mold has begun to proliferate on the roots' surfaces. The oxygen liberated from the hydrogen peroxide is destructive to single-celled organisms and is administered in dosages which vary with the concentration of the peroxide. Typically several tablespoons of 3.5% solution per gallon or more of water are used. The temporary rise in the oxygen level is only minimally damaging to roots, while eradicating the water-borne mold can significantly increase yield or even save a crop's viability.