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Environment, VPD & Climate Control

Temperature and humidity management is the layer most growers underinvest in relative to how much it actually controls plant performance. These guides cover VPD and why it matters more than humidity alone, cooling a grow tent through Australian summer, dehumidifier selection, and the ventilation setup that keeps mould and mildew from establishing in the first place.

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Inline Fans & Carbon Filters vs Bunnings: What Actually Controls Heat and Smell
Quick Answer: Inline Fans and Carbon Filters vs Bunnings Bunnings sells bathroom and shed exhaust fans -- not designed to push air through ducting and a carbon filter. The number that matters under load is static pressure, not advertised airflow on an open bench test. Bunnings does not stock a grow-room carbon filter at all -- there is no in-store odour control option for hydroponics. A mismatched fan and filter means reduced airflow, heat build-up, and odour escaping despite the filter being installed. For a wardrobe-sized propagation box with no... Read more...
The Real Order of Priority in Hydroponic Growing: Environment, Light and Nutrients
The Real Order of Priority in Hydroponic Growing: Environment, Light and Nutrients
Quick Answer: The Real Order of Priority in Hydroponic Growing Pot size and root zone come first. An oversized pot is just as limiting as an undersized one, and a... Read more...
Why Your Hydroponic Nutrients Stop Working at Night
Quick Answer: Why Hydroponic Nutrients Stop Working at Night Plants don't stop physiological activity when lights go off, since nutrient transport, cellular repair, and respiration continue through the dark cycle. In sealed tents, humidity rises sharply within the first hour of lights off as temperature drops and air holds less moisture. High night-time humidity reduces leaf transpiration, which directly reduces calcium transport from roots to growing tissue. In cold climates (southern Victoria, Tasmania), the opposite occurs, with cool dry air pulled in by extraction dropping RH rapidly overnight. Condensation forming... Read more...
Grow Room Dehumidifier: What It Does, When You Need One and How to Choose
Quick Answer: Grow Room Dehumidifier Guide Australia Target RH: 70 to 80% in seedling and early veg, 50 to 70% in late veg, 40 to 50% in flower, below 40% in final 2 weeks. Size your dehumidifier for the volume of your grow space plus the moisture load from transpiring plants, since undersizing is the most common mistake. A dehumidifier that drains continuously via gravity to a floor drain eliminates the need to empty tanks manually. Dehumidifiers generate heat, so factor this into your temperature management, particularly in Australian summer.... Read more...
Relative Humidity vs VPD: Why Dialling In Your Grow Room Environment Changes Everything
Most growers track relative humidity, but VPD is the metric that actually drives transpiration, nutrient uptake, and yield. Learn how to dial in your grow room environment for maximum performance. Read more...
VPD in Australian Grow Rooms
Quick Answer: VPD for Australian Grow Rooms VPD measures the air's capacity to pull moisture from your plants, more accurate than RH alone. Target VPD: 0.8 to 1.0 kPa in early veg, 1.0 to 1.2 kPa in late veg, 1.2 to 1.6 kPa in flower. Under LED lighting rooms run cooler, so the same RH produces a lower VPD than under HPS, meaning you likely need lower humidity than you think. High VPD: plants stress and wilt. Low VPD: slow transpiration and calcium lockout. Fix VPD by adjusting temperature first,... Read more...
How to Cool a Grow Tent During Australian Summer
Quick Answer: How to Cool a Grow Tent in Australian Summer Target canopy temperature: 22 to 28 degrees Celsius during lights on. Above 30 degrees photosynthesis declines. Above 35 degrees plants show visible heat stress. Step 1: Optimise extraction, since an undersized inline fan cannot manage temperature spikes during a heatwave regardless of other changes. Step 2: Switch from HPS to LED, which reduces the heat load inside the tent by 40 to 50 percent at equivalent light output. Step 3: Cool the room around the tent, not just inside... Read more...