Hydroponics relies solely on water as both a nutrient carrier and growing medium. However, should we submerge all the roots to make sure it’s getting all that nutrient-rich water?
Not all the roots in hydroponics should be submerged because the unsubmerged roots act as “air roots” which absorb oxygen which is necessary for aerobic respiration in plants. Submerging all the roots would lead to “drowning” causing root rot and even death if left untreated.
The perennial problem of roots and watering is tackled uniquely by hydroponics and the different techniques under it. It’s a good idea to get intimate with how each technique deals with the problem and the recommended practices associated.
Table of Contents
- 1 Should All The Roots Be Submerged?
- 2 What Happens When All Roots Are Submerged?
- 3 What Do The Submerged Roots Do?
- 4 What Do The Unsubmerged Roots Do?
- 5 Different Hydroponic Techniques and Roots Nutrient Absorption Process
- 6 Recommended Practices For Each Technique
- 7 Optimal Water Conditions
- 8 Takeaway
- 9 Sources
Not all root systems should be submerged in hydroponics because some roots need to be exposed to the air to allow breathing (the process of aerobic respiration). Plants also need oxygen to grow and convert glucose made during photosynthesis into energy, better known as adenosine triphosphate (ATP).
This is why even in soil cultivation, aeration is important. The soil serves as a site for oxygen exchange for aerobic respiration. Certain qualities such as the water retention and drainage of soil are often weighed against one another to strike a desired balance depending on the plant species, climate, and other growing conditions.
The plant’s health will deteriorate towards death when all roots are submerged because they cannot “breathe.” Plants cannot initiate the process of aerobic respiration which prevents them from converting glucose into energy. This makes the roots vulnerable to diseases such as root rot.
Hydroponics, despite relying solely on water as a nutrient medium, has its built-in safeguards against these negative consequences of waterlogged conditions.
The roots submerged in the nutrient-rich water draws nutrients and dissolved oxygen for the plant. These are necessary functions for photosynthesis and aerobic respiration. In essence, the submerged roots in hydroponics function no different from roots buried in dirt in soil cultivation.
Submerged roots are most commonly seen in deep water culture (DWC), nutrient film technique (NFT), and ebb and flow. This is because those systems have the plant roots come into closer direct contact with the nutrient solution compared to other techniques.
The unsubmerged roots prevent the plant from “drowning.” They are responsible for absorbing oxygen in the air which the plants use for the vital metabolic process of aerobic respiration. This produces energy in the form of ATP and two waste products, water (H2O) and carbon dioxide (CO2).
The unsubmerged roots act as “air roots” for the absorption of oxygen so they fulfill a vital job in the plant’s biological processes as much as the submerged roots.
Different techniques bring nutrients to the root system in different ways. Some techniques apply the nutrient-rich water directly to the roots while other techniques apply it in conjunction with growing mediums.
The common description of hydroponics is “growing plants IN water.” This is somewhat incorrect as it is more accurate to say that it’s “growing plants on or primarily with water.”
For example, nutrient film technique (NFT) and deep-water culture (DWC) grow plants “ON water.” The root system is only ever partially submerged and “on water” because they are placed in a growing medium or net pot and suspended above the nutrient-rich water
However, other techniques such as ebb and flow, wick, drip, primarily use water as a nutrient carrier in conjunction with growing mediums. The nutrient-rich water enhances the potential of the growing medium.
Lastly, aeroponics is the unique outlier. It brings sustenance to the root system of a completely suspended plant by use of a nutrient-rich mist.
Given that each technique applies water to the root system, there are distinct recommended practices for each which aim to maximize growth. These include distance, angle, cycle, and duration of watering.
Let’s discuss the recommended practices for each technique one by one.
In deep water culture (DWC), there should be air passing between the root system in the growing medium and the water level of the nutrient reservoir. The general rule is that the water level is approximately 1 inch from the bottom of the net pot with a growing medium. This should be adjusted accordingly based on the root system’s reach.
The reason being is that a net pot with a growing medium will absorb the water due to the bubbling caused by the air pumps and air stones. This will make the growing conditions “too wet” thereby drowning the plant or causing root rot. The growing medium also serves as a site for gas exchange and a contingent buffer for nutrients. Logging it with water will negatively affect the plant’s health.
If neoprene collars or alternatives are used, the water level should be slightly above the bottom of the net pot since the open space in the net pots would serve as the site for gas exchange. More importantly, the plants require immediate access to nutrients since there is no buffer unlike when there is a growing medium.
In nutrient film technique (NFT), the root system is not submerged but rinsed by a nutrient film – a 0.04-0.08 inch (1-2 mm) thin stream at an inclined angle. It is recommended that the channel (gully) in an NFT system should be sufficient to facilitate gas exchange and release, as to prevent debris from building up in the root system.
The nutrient film technique has little chance of overwatering or drowning the plant unless the flow rate is too high or if there are hindrances which make the water gather and pool.
In an ebb and flow system, the root system and growing medium are periodically flooded by the nutrient reservoir. It is recommended flooding should not take more than five (5) minutes and that there be 3.75 gallons per square feet of grow tray to facilitate rapid growth.
The ebb and flow system has the benefit of facilitating oxygen exchange every cycle. Every flooding causes the deoxygenated air out of the growing medium and the root system area whereas every draining causes oxygen-rich air to go back in.
In low-pressure aeroponics (LPA), droplets of nutrient-rich water are sprayed 24/7 on the root system via a sprinkler system. The NASA-developed high-pressure aeroponics (HPA) uses high-pressure 100 psi misters which provide the root system with nutrient-rich droplets measuring 20-50 micrometers. The angling and distance of the sprinklers/misters depend on the engineering of the system.
LPA is more easily available to the average gardener because of the lower material requirements. However, HPA is more efficient and effective because root systems are more receptive to absorbing nutrients carried by 20-50 micrometer droplets. HPA also has the added benefit of allowing more oxygen accessible by the root system.
In a drip system, tubes connected to the nutrient reservoir “drip” nutrient-rich water into the growing medium and the root system at set intervals. It is recommended that the rate should be 8-20 gallons per hour and repeated 2-3 times a week. However, this is not a hard-and-fast since it depends on the climate, growing medium, and plants grown.
Drip system is a simple and effective method of applying hydroponic principles to soil cultivation. The principles are basic and easily understood. However, it has the added hassle of leaving to the gardener the task of finding the optimal drip irrigation schedule and amount. This is a task which requires trial and error and a lot of observation.
The University of Pennsylvania has an extensive study and formula for you to better “dial in“ the optimal drip irrigation schedule and amount. The results of this study are very interesting.
Vegetable crops require 1-1.5 acre-inches of water per week.
The wick system uses wicks to draw via capillary action the nutrient-rich water from the nutrient reservoir to the roots and the growing medium. It is recommended that there be one wick per plant, or two or more wicks if the plant is water-hungry. Recommended wick materials are:
The benefit of a wick system is its ease of use and natural progression from conventional soil cultivation to hydroponics. A regular gardener would not be lost when trying to apply a wick system to their potted plants except that the growing medium should be replaced with either perlite, vermiculite, or other soilless mixes.
Kratky systems are essentially deep water culture (DWC) systems without any air pumps. The same recommendations in DWC apply wherein there should be at least a 1-inch space between the net cups and the nutrient reservoir to let the roots absorb oxygen. The water level should be adjusted accordingly that they do not submerge all the roots.
Kratky systems have the benefit of being fairly simple to implement and do not require any active components, making it perfect for beginners. However, they are not suited for larger plants or long-term planting. Additionally, the lack of an air pump may make the plant oxygen-deprived if the air roots are closed off to other sources of oxygen.
There are several ways to optimize the water condition in hydroponics for better growth and yield. These means can also prevent complications such as disease, root rot, and nutrient deficiencies.
The ideal water temperature in hydroponics should be from 65-80° F (18-26° C). Cooler water temperatures mean that water holds much more dissolved oxygen (DO) compared to warmer water. This is vital for hydroponics because the submerged roots are also capable of absorbing oxygen in the water.
The metabolic process of plants is influenced by the water temperature. Having a consistent temperature prevents plant shock if any abrupt temperature changes occur.
To that effect, some hydroponic growers choose to add chillers in their nutrient reservoir, especially for DWC systems.
Dissolved oxygen is necessary for many active hydroponic systems since it ensures that even the submerged roots can receive oxygen. It is recommended that an air pump be rated at least 1 LPM (liter per minute) for every liter in your system. Dissolved oxygens levels equal or above 5 mg/L are ideal.
This problem is most applicable in DWC systems because of the limited airflow between the grow tray and the nutrient solution in the reservoir. This is why an air pump is a necessity in DWC systems rather than an option.
For smaller systems, a value air pump like this on Amazon is an interesting option.
For larger systems, a commercial air pump like this one on Amazon would do the job. It has the added benefit of being able to pump air in six (6) locations!
- Not all of the roots in a hydroponic system should be submerged. The unsubmerged roots serve as air roots which absorb oxygen needed for aerobic respiration.
- Different systems “submerge” their roots with nutrient-rich water in unique ways. DWC, NFT, Aeroponics, and Ebb and Flow systems have more direct contact with water whereas Wick and Drip systems come into contact with water via the growing medium.
- There ways to optimize the water in hydroponics to make it more ideal to plants: (1) maintaining the water temperature to
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