Why Spraying Sulfur in a Grow Room Is A Bad Idea!

Sulfur has been a staple in horticulture for generations, and wettable sulfur is still an effective tool for managing powdery mildew and certain pests. It works well in greenhouses where airflow is high and electronics are minimal. But in modern, sealed indoor grow rooms, wettable sulfur can create problems many growers don’t anticipate.

We aren't against the use of sulfur in horticulture but we do think that you should be aware of the potential pitfalls of using sulfur in sealed/controlled rooms.

This discussion is not about sulfur burners. Wettable sulfur behaves differently, but it still carries risks when used in enclosed, tech‑heavy environments.

How Wettable Sulfur Behaves Indoors

Wettable sulfur is applied as a foliar spray, typically with lights off. Once it dries, it leaves behind a fine sulfur powder that settles on plants, surfaces, and - most importantly - your electronics.

A single application may not cause issues. Repeated use, however, allows sulfur dust to accumulate in places you don’t want it: inside fixtures, on circuit boards, in fans, and throughout ventilation systems.

Wettable sulfur does not directly release sulfur dioxide gas like burners do, but when the dust encounters moisture, it becomes corrosive.

Why Electronics Are Vulnerable

Indoor grow rooms rely on sensitive equipment, including:

• LED fixtures and drivers
• Inline and oscillating fans
• Environmental controllers
• pH and EC meters
• CO₂ controllers and humidity sensors
• Relays, circuit boards, and automation systems

These components contain exposed copper, silver, solder joints, and metal contacts. Sulfur dust reacts with these metals - especially in humid environments where it becomes metal sulfide. This corrosion is slow and often invisible until your equipment fails. 

Common symptoms include:

• darkened or tarnished contacts
• increased electrical resistance and higher power draw
• inaccurate sensor readings
• premature LED driver failures
• fans becoming noisy or seizing

Why Enclosed Grow Rooms Are At Higher Risk

Compared to greenhouses, sealed indoor grow rooms create conditions that amplify sulfur’s impact:

• high humidity accelerates sulfur–metal reactions
• limited ventilation allows dust to linger
• constant airflow pulls particles into electronics

Even if the room looks clean, fine sulfur particles can accumulate quietly over time.

Plant and Environmental Considerations

Beyond equipment concerns, wettable sulfur has other limitations:

• it can cause leaf burn under strong lighting or at higher temperatures
• it may disrupt beneficial microbes (primarily fungi based microbes)
• it can react negatively with certain foliar products, especially oils

These issues don’t make sulfur unusable, but they do require careful timing and management.

Is Wettable Sulfur Unsafe Indoors?

Not inherently. The problem is where and how it’s used.

Wettable sulfur is generally safe outdoors and in ventilated greenhouses. In sealed indoor grow rooms, the main risk isn’t toxicity - it’s long‑term equipment degradation!

Growers who choose to use it indoors should consider:

• covering or removing electronics
• increasing ventilation during and after application
• avoiding repeated or heavy use
• cleaning surfaces thoroughly afterwards

Better Options for Enclosed Environments

For growers who want pest and disease suppression without risking electronics, non‑corrosive alternatives are often a better fit. These products rely on physical or biological mechanisms rather than elemental sulfur, making them safer for sealed, tech‑dense environments.

Locally Available Alternatives to Sulfur Sprays

Dominate – Eco Plant Wash (NZ) A maintenance‑focused plant wash that helps prevent issues before they start. Regular use supports plant health, reduces dust buildup, and helps avoid pests and mildews.

FIND IT HERE

Central Coast Products – Green Cleaner (USA) A similar plant‑wash‑style product with a comparable mode of action. Again, prevention beats reaction - stop treating problems and start avoiding them. 

FIND IT HERE

FUN FACT: White Island is an active volcano (located in the Bay of Plenty, NZ) that was once a SULFUR MINE. Sulfur was mined from the volcano from the 1880's till the early 1900's - in 1914 ten miners where killed by a landslide which lead to the closure of mine. White Island is considered to be the most active hydrothermal system on the planet. 

Picture from White Island prior to its closure

Now go grow some plants!