Everest Fernandez invites us to reconsider dissolved oxygen in our modern grow rooms.

With the advent of LED grow lights and the accompanying trend of running our rooms at higher air temperatures, indoor growers arguably need to pay more attention than ever to dissolved oxygen (DO) levels in irrigation water and nutrient solutions.

Self Assessment

Before we explore the details, consider your growing practices. How many of these statements apply to you?

1. You cultivate fast-growing, warm-season plants.
2. Your setup includes high-intensity LED grow lights.
3. Your nutrient reservoir is located within your grow room.
4. You incorporate beneficial biological products (e.g., mycorrhizae, bacteria).
5. Your growing medium is relatively restrictive (soil, peat, coco coir, or stone wool).
6. You operate a recirculating hydroponic system.
7. You maintain high nutrient concentrations in your solution.

The more points that resonate with you, the more critical dissolved oxygen becomes for your garden’s success. Even if you only checked one box, understanding DO is vital for optimizing plant health.

The Basics of Dissolved Oxygen

So, what exactly is dissolved oxygen? Simply put, it’s the amount of free oxygen molecules dispersed in your water or nutrient solution. It’s not the oxygen in H₂O molecules or the tiny bubbles from your air stone, but rather, separate O₂ that has mixed into the liquid at a molecular level. Imagine sugar dissolving in coffee – it’s present but invisible to the naked eye.

Why is Dissolved Oxygen Important?

DO forms the foundation of root health, supporting overall plant vitality. Adequate DO levels enable efficient aerobic respiration, the process by which roots convert nutrients into energy for growth. In hydroponic systems or container growing, where roots are confined, maintaining high DO helps prevent root suffocation, stunted growth, and increased susceptibility to diseases like root rot.

The Interplay of Your Growing Environment and Dissolved Oxygen

Let’s reconsider those initial seven statements and examine how different growing conditions impact DO levels and why they matter:

1. Fast-growing, warm-season plants: These crops have higher metabolic rates, demanding more oxygen for respiration. As they develop quickly, their need for oxygen in the root zone intensifies.
2. High-intensity LED grow lights: These powerful lights boost photosynthesis, increasing metabolic activity. This heightened plant activity raises oxygen demand in the root zone, necessitating higher DO levels.
3. In-room nutrient reservoirs: When your reservoir rubs shoulders with your plants, it’s subject to the same elevated temperatures. Warmer water holds less oxygen, increasing the risk of DO depletion, especially in LED-lit environments.
4. Beneficial biological products: While microbes like mycorrhizae and bacteria enhance nutrient uptake, they also consume some of the available dissolved oxygen. High DO levels are crucial to prevent oxygen deficiency in the root zone.
5. Restrictive growing media: Media with smaller pore spaces, such as peat or coco coir, can limit air exchange and oxygen diffusion. Even professional media like stone wool, designed for water retention and aeration, benefit from high DO levels in the nutrient solution.
6. Recirculating hydroponic systems: These setups can accumulate organic matter and microbial activity over time, both of which increase oxygen consumption. Regular monitoring and maintenance of DO levels are necessary to avoid oxygen depletion.
7. High nutrient concentrations: Concentrated nutrient solutions can increase osmotic potential, potentially reducing oxygen availability to the roots. Maintaining optimal DO levels becomes even more critical under these conditions.

Optimal Dissolved Oxygen Levels for Thriving Plants

For fast-growing, warm-season plants, aim for DO levels between 6.0 to 8.0 mg/L in your nutrient solution. Understand that the DO saturation point decreases as temperature increases. For instance, water at 18°C (64.4°F) has a DO saturation point of 9.45 mg/L, but this drops to 7.58 mg/L at 30°C (86.0°F). Generally, lower temperatures closer to 18°C are better for maintaining higher DO levels, especially in hydroponic systems.

How To Boost Dissolved Oxygen Levels

1. Aerate your nutrient solution: Place an air stone connected to an air pump at the bottom of your nutrient reservoir. This continuously infuses air (containing 20% oxygen) into the water. Constantly running the pump is more effective than intermittent aeration, especially in warm environments or systems with large root masses.
2. Chill your nutrient solution: Since warmer water holds less oxygen, aim to keep your nutrient solution between 18°C and 22°C (64°F to 72°F). If an aquarium chiller isn’t feasible, consider relocating your reservoir to a cooler area to prevent temperature-induced oxygen depletion.
3. Optimize water movement: Use a small water pump to periodically circulate your nutrient solution. Good circulation prevents stagnant areas where oxygen might be depleted and ensures even distribution throughout the system. Be aware that constant pump operation can generate heat, so monitor temperatures closely.
4. Employ advanced oxygenation techniques: 
   • Electrolysis or nanobubbles can infuse water with pure oxygen, significantly enhancing DO levels.
   • Products containing hydrogen peroxide (H₂O₂), like OxyBlast and OxyPlus, can add free oxygen to the nutrient solution. Use these carefully to avoid harming beneficial microbes or plant roots.
   • Venturi injectors can be integrated with nutrient dosing systems to oxygenate the solution before it reaches the plants.

5. Choose high-drainage growing media: Well-aerated media such as a 50/50 mix of coco and perlite or expanded clay balls require more frequent irrigation, which can be automated. This ensures that plant roots have continuous access to oxygen-rich solution.
6. Implement a regular maintenance schedule: Consistently clean and maintain all aeration and circulation equipment. Clogged air stones or dirty pumps can reduce the efficiency of oxygenation efforts, leading to lower DO levels.

Measuring Dissolved Oxygen: Tools of the Trade

The cost of handheld DO meters varies widely based on features, durability, and precision. For most hydroponic applications, the Hanna HI-9147-04 with a galvanic probe is an excellent choice, though it comes with a price tag upwards of $750. If you’re looking for a more budget-friendly option, consider the Milwaukee MW600, which retails around $150.