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I’m Dr. Russell Sharp, creator of Gold Leaf (also known as Liquid Gold in the UK)—the all-in-one fertilizer that takes you from seed to harvest.
Today we’re talking about a topic that might surprise many growers: ozone. While it’s famous for protecting us from UV radiation in the upper atmosphere, down here in the troposphere, ozone becomes a major threat to your plants—especially in urban grow environments.
We often associate ozone with the ozone layer, a protective shield in the stratosphere that blocks harmful ultraviolet rays. But at ground level, it’s a toxic air pollutant that harms both humans and plants.
Historically, agricultural chemicals like methyl bromide contributed to ozone layer depletion. Thankfully, it was banned globally thanks in part to environmental pressure spearheaded by world leaders, including Margaret Thatcher.
The ban on methyl bromide also led to the rise of hydroponics, since growers could no longer rely on chemical soil sterilant. That’s a win for the environment—and for hydroponic innovation.
In urban environments, ozone pollution forms when nitrogen oxides (NOx), carbon monoxide, and volatile organic compounds react with sunlight. This contributes to photochemical smog, infamous in cities like Los Angeles and historic Liverpool.
But for growers, the real danger is this:
👉 Ozone is highly toxic to plants.
It causes:
The worst part? It’s hard to diagnose, and few growers even realize it’s affecting their crop.
Ironically, high ozone days often coincide with what many call “beautiful weather”:
If your indoor hydroponic setup is in a city, and you’re venting outside air in during these conditions—ozone might be infiltrating your grow room.
1. Use Activated Charcoal Filters – On the Inlet
Most growers already use carbon filters on the exhaust, but few think to filter incoming air. Installing a carbon filter on the inlet can drastically reduce ozone levels entering your space.
2. Monitor When Possible
Ozone monitors are expensive, but even being aware of the risk during summer heatwaves can help you adjust ventilation or supplement with antioxidants.
3. Apply Antioxidants to Plants
4. Use Tolerant Plant Varieties
Some plants are naturally more tolerant of ozone:
In small, controlled doses, ozone is used for sterilization—in water and air—to kill bacteria and pathogens. But don’t confuse this with a plant-growth benefit. Too much ozone damages crops. If you do use an ozone generator, make sure plants are not directly exposed.
Ironically, while ozone can stress plants, it also triggers antioxidant production, which could be leveraged near harvest for higher antioxidant content in leafy greens. However, this is advanced territory and not recommended for beginners.
With growing adoption of electric and hydrogen vehicles, urban ozone levels may decrease over time. That’s great news for city-based hydroponic growers. Until then, it’s essential to recognize ozone as a hidden, airborne stressor and adapt accordingly.
Ozone might not be something you think about daily as a grower—but it should be. It’s one of the most underestimated threats in indoor hydroponic systems, especially during hot summer months in cities.
Simple upgrades like an extra inlet carbon filter could make a major difference in protecting your crops.
Article by Dr Russell Sharp
If you would like to keep up to date with subjects just like this, you can listen to both our podcasts! Links can be found bellow:
Hydroponics Daily Podcast: https://open.spotify.com/show/207T7p7fw9sPjINfSjVXW2
Cereal Killers Podcast: https://t.co/eSEbBkTVHl