We often talk about the optimal temperature for growing cannabis indoors, but there is one thing that we always overlook - the root zone temperature.

When your plants have enough light, nutrients, water, carbon dioxide, ideal humidity, temperature, etc., you also need to pay attention to the root environment of cannabis. If you don’t have an optimal root zone environment, you’re going to have yellow leaves, discolored leaves, and purple leaves. Without a healthy root system, cannabis will not reach its full potential.The root system provides support for the above-ground part of the plant, absorbs water and nutrients from the soil to meet its own growth, and is an important vegetative organ of the plant.

Root zone temperature is a key factor affecting root nutrient and water uptake. The ability of water to transport nutrients is significantly reduced when the root system was in a low root temperature environment.
Root zone temperature is closely related to root respiration. Studies have shown that low root zone temperature inhibits root respiration and ultimately affects nutrient absorption and root growth; and in a low-temperature environment, with the increase of root zone temperature, root respiration The effect will gradually increase.
Root zone temperature will affect the synthesis, content, and activity of substances in the root system. Crop roots contain a variety of enzymes, such as catalase, peroxidase, superoxide dismutase, etc., in addition to other substances, such as malondialdehyde, soluble sugar (sucrose), etc.; and these substances and crops' nutrient composition (sugar, moisture), respiration, stress resistance, and disease resistance are all related.

Within a certain temperature range, the higher the root zone temperature, the faster the growth and development of crops. Roots will develop and function optimally when cannabis root zone temperature is in the range of 68°F-78°F. Any fluctuations in temperature should be kept to a maximum of 5 degrees for optimal root development.

In hydroponic systems, you’ll want to keep the temperature of your water between 66°F and 77°F. Within this temperature range, more oxygen can be ensured to dissolve in the water, providing enough oxygen for root respiration. Add ice or cold water to the reservoir regularly to cool it down to keep the temperature of the reservoir at its best.

Plant roots cannot regulate their own temperature, and once the root zone temperature exceeds the perfect zone, it can no longer provide the rest of the plant with an ideal level of materials. The greater the fluctuation in temperatures in a 24-hour period, the more stressed the root system becomes. The more stressed a root system is the more problems a plant will have both physically and pathologically and will become increasingly susceptible to pathogens and insects. Therefore, it is necessary to monitor and manage the root zone temperature.Measuring root zone temperature is also measuring the temperature of the plant growth medium. You just need a soil thermometer or a barbecue thermometer, which can be bought at the hardware store for about a few dollars. The soil temperature can be read by inserting a thermometer into the soil.When the lights go on, the air temperature rises and as a result the soil temperature will rise too. It takes a while before the soil warms up (just as it will cool down slowly after the lights are turned off). But it’s not only the air that influences the soils temperature. The material, depth (volume) and moisture level also changes its ability to give off or retain heat.

If plants are grown with the root temperatures lower than the optimum, the plants grow slower because their metabolism is slower. Concrete floors are really cold in winter and the plants don't grow well. Because concrete basically takes heat away from the root zone of the cannabis plant and cools it down. So there will be some issues with the root zone staying at the right temperature. Insulating the pots from the cold floor is always a good idea.

Likewise, if the roots get too hot, growth will cease, and plant health will quickly deteriorate. You can help control this through the temperature of the nutrient solution. If your root zone is a little too high, you can always balance it out by using a cooler nutrient solution.

The health of the roots is not only affected by the root zone temperature, but also by the oxygen and nutrients in the root zone. While focusing on the root zone temperature, other factors should also be optimized.