pH, water temperature, EC/TDS, that's all you need to know to keep your hydroponics system healthy, right? Not so fast. Dissolved oxygen (DO) is the measure of the oxygen content in your water and it is one of the underrated parameters in hydroponics, regardless of what type of system you are using to grow your plants. In this post we explore why dissolved oxygen is important in hydroponics, how to setup your system to maximize the oxygen in your water, and ways to track your DO and make sure your plants are as healthy as possible. Click to read below.
Dissolved Oxygen and Hydroponics:
- Like us, plants need to breath air. They don't do it through their leaves, but through their roots. This is why when you're gardening in soil, you often see fertilizer mixes with perlite in them. Perlite contains no nutrients, but it creates lots of great little gaps for oxygen to permeate down from the surface and reach plants' roots. Similarly, this is why when planting starts, you don't compress the soil - those baby roots need to breathe! Even the most tolerant plant to low DO situations (looking at your lettuce) has a minimum threshold before it will start to slow its growth and will eventually suffocate and die if the DO is too low. Obviously this is not an ideal if you are going for maximum growth.
- When DO drops too low in your water, you open the door to lots of nasty things. The enemy of your enemy is your friend. If you're growing hydroponically, your enemy is anaerobic (aka oxygen hating) bacteria. Ever smell something rotting? Or a swamp? That's anaerobic bacteria. Anaerobic bacteria are essential in the world because they are excellent at breaking down dead organic things, turning them into their base nutrients. That smell is the ammonia and other gasses they give off in the process. Two bad things happen when your system starts going anaerobic. First, when you're growing plants, having anaerobic bacteria means something is dead and breaking down. Root rot is a common disease caused by low DO, as the anaerobic bacteria start to eat at your plants' exposed roots. It can take a long time to show at the leaf level, so, if you aren't checking your root zone regularly, you can be slowly killing your plants without even knowing it! Second, aerobic bacteria (oxygen loving) create beneficial relationships with your plants and will help fend of pathogens and disease. When DO drops and anaerobic bacteria takes over, your aerobic bacteria will go dormant, and your plants will be far more susceptible to disease.
Maximizing Your DO:
Let's start at the basics. Deep water culture (DWC) provides the least natural DO to your plants roots, and therefore requires an air stone (see image) to artificially keep water oxygenated. Similarly, because DO has an inverse relationship with water temperature (as WT goes up, the oxygen carrying capacity of water goes down), you should place your DWC system carefully or potentially insulate your reservoir to protect against your water temperature getting too high. One of the big drawbacks of DWC is that should your air stone fail, your plants can suffocate very quickly as there is no moving water.
Nutrient film technique or NFT came about to help solve for the oxygen issues. In NFT, plants are placed in long tube (PVC, gutter materials, etc.) that is at a slight decline. As water flows from the top to the bottom, there is a thin trickle that is just enough to cover the roots, but is not a deluge. The angle of your NFT is very important for this reason. Too shallow and there will not be enough water flow and your plants will suffocate. Too steep and there will be too much water flow and your roots will dry out. The thin "film" of water that covers the plants' roots allows them to absorb ample nutrients and, with its ample surface area, absorbs a lot of oxygen that are also available to the roots.
The latest hydroponic system, aeroponics, was developed to solve for DO. In aeroponics, the nutrient solution is sprayed onto the plants' roots as a fine mist. The spray pump turns on at regular intervals to always keep the roots just moist enough to not dry out but at the same time have access to all of the environmental oxygen they want. The more oxygen available to plants the faster they will grow (similar to CO2). That's why, while aeroponics is very difficult to master, it is one of the hottest growing techniques right now.
Monitoring Dissolved Oxygen
A dissolved oxygen monitor. Shameless plug for OsmoBot here, (it is our blog, after all) but a DO monitor in your nutrient reservoir will make sure that the solution flowing out to your plants, regardless of your system will have enough DO to keep them healthy and happy. If something does go wrong, you'll have the chance the catch it way before it becomes a problem.
Flow meter. One of the biggest causes of low DO is a backed-up pipe or pump. A flow meter is perfect for these situations, but the existing ones largely require you to be in person to read them. We are working on this one.
Power outages. All hydroponic systems require a pump at some point and without power, they will stop pumping. Without your pumps running, whether they are moving air or water, your DO will drop to critical levels, unless you take an outside measures. Backup generators are great, as are lost connection alarms and autodialers. While it's not AS critical as in aquaculture to respond quickly to a power outage, it can do a lot to keep your plants happy and healthy.