Hi Nico,
We have had some decent luck growing our first plants recently, but the yields were low and I can see the plants were not fully developed. While most conditions such as medium and lighting were close to ideal, I am not sure our environment is optimal—specifically in regards to temperature. Can you speak to optimal temps for the plant and root system and how fluctuations may affect plant growth? Many thanks!
– Jordy via NicosNuggets@hightimes.com

Greetings, Jordy! Thanks for visiting HIGHTIMES.com and sending in a question. Environment—and temperature in particular—is one of the hardest aspects for the indoor grower to master.

Assuming your lighting set-up is ideal and providing enough light energy to your plants as you stated, then temperature could very well be a factor in your plants’ slow development. While temperature will not affect the rate of photon (light energy) capture from your lamp, it can heavily influence the rate of sugar production during photosynthesis. Sugar, in the form of glucose, is the plant food created via photosynthesis and is central to a plant’s growth and development.

To illustrate this point, let’s use a garden that is operating at an optimal temperature of 80°F. At this temperature during photosynthesis, a plant will breathe in CO2 to extract the carbon molecule to create glucose. At 80°F, this process works at twice the rate it would at 66°F. Conversely, at 86°F and above, the process also starts to slow down significantly. This means that there is a “sweet spot,” or optimal temperature zone (between 72°F and 82°F), that is optimal for sugar production and hence better for plant growth. The slower the growth rate, the smaller the plant will be—and the lower the yields will be.

Garden temperature is a critical factor in photosynthesis and plant development.

Garden temperature is a critical factor in photosynthesis and plant development.

In terms of fluctuations, extreme temperature swings can devastate gardens. Plants can and will stress easily if their environment shocks them enough. At temperatures near freezing (in the mid- to low-30s), water inside the plant can begin to freeze and explode cell walls. Conversely, at temperatures higher than 92°F, enzyme function and reactions start to fail. At temps over 100°F, the inner pressure of water evaporation begins to rise steeply and can again destroy cell membranes and functions.

Root zone temperatures are equally important as chemical reactions happen at a faster rate in optimal temperatures. These reactions are the mineral uptake from the nutrients we give plants for use in photosynthesis. The better and faster these reactions occur, the quicker and more abundant food the plant will have. The ideal root zone temp for cannabis plants is around 75°F and should always be about 5 degrees cooler than the garden temperature.

Soil and root zone temps can be better controlled with a top layer of perlite.

Soil and root zone temps can be better controlled with a top layer of perlite.

Remember, good heat exhaust from the top of your growroom and cool, fresh air intake at the bottom of your garden can go a long way in helping keep heat issues in check and stable temps in your garden. Your plants will be happier, healthier and appreciate the stable environment.

Thanks for reading everyone and remember: Grow… And help the world grow, too!

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Don’t miss the previous Nico’s Nuggets: Plant Containers for Beginner Growers

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