Temps and Humidity: A Guide

Tara | January 18, 2022
leaf close up
Temperature & Humidity

Optimal air temperate and humidity ensures that adequate carbon dioxide (CO2) is available to the stomata. Excessively cold or hot temperatures reduce chemical/photosynthetic activity within the plant. Similarly, excessive humidity will reduce the plant’s ability to process CO2. This is because moist air suffocates the stomata, reducing its ability to collect the CO2 needed for vigorous growth. In addition to this, moist air reduces the plant’s ability to transpire. Transpiration is the movement of water from the roots to leaf surface – driven by evaporation. At high humidity, evaporation is low, so transpiration slows down. As a result of this, growth is adversely affected.

Temperature affects the root system differently from the stem, leaf, and flower structures. Excessive water temperatures will reduce available oxygen to the root zone. The root system can become damaged because of this, which in turn affects the plant’s ability to uptake nutrition. Oxygen starvation resulting from excessively warm water is the primary cause of root rot in hydroponic systems.

What Temperature Should My Grow Room Be?

Recommended day temp is 26 - 28 °C

Recommended night temp is 20 - 23°C

Try to minimise the swing between night and day temperatures. Use a thermometer to record temps/swings. A thermostat is also a useful tool for controlling temps.

What Humidity Should I Maintain?

Clone - above 80%

Grow stage - 60%-80%

Bloom stage - 50%-60%

When humidity is too low, an Evaporative Cooler can increase humidity levels. When humidity is too high, consider extra ventilation or a dehumidifier. A hygrometer is a useful tool for measuring humidity.

How Much Ventilation is Necessary?

The purpose of ventilation is to maintain temps and humidity in the centre of the plant canopy. Generally, it is preferable to have too much ventilation than not enough. Replenishing the air in the room provides more CO2 for your plants.

Don't Overlook Nutrient Solution Temperature

A crucial, yet often overlooked factor in hydroponic environmental control is the temperature of the nutrient solution.

Why Does Temperature Make a Difference?

The temperature of the nutrient solution impacts the amount of oxygen that can be transported to the roots. Cooler water is able to retain more oxygen, while warmer water retains less oxygen.

What is the Optimum Water Temperature Range?

The optimum water temperature range is 18-22°c. The ideal temperature is 20°c.

At 25°c water can hold 5ppm of oxygen. At 20°c water can hold 8ppm of oxygen.

Problems Resulting from Incorrect Water Temperature

When the nutrient solution is too warm, plants may begin to suffer from heat stress. Symptoms of heat stress include wilting and root diseases. Warmer water temperatures also provide the optimum environment for pathogens (damaging microorganisms, fungi, and bacteria) to multiply in the nutrient solution, on the plants roots and in the root zone. The beneficial microorganisms that keep pathogens in check can't survive in the warmer water, allowing pathogens to multiply. Rotting roots caused by high water temps also feed the pathogens.

Cold nutrient solution problems don't occur as often, especially in Australia's relatively warm climate. However if the nutrient solution is too cold, it can stunt and slow plant growth.

Controlling the Nutrient Solution Temperature

We recommend the use of a water chiller during the warmer months. An effective water chiller can quickly chill 2 x 200L barrels of nutrient solution. A water chiller can also be used to regulate the temperature of multiple Turboklone stations.

We recommend the Hailea HC series water chillers. For more information, drop in for a chat or contact us anytime.

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