Most growers ask this question because they want to find the ideal temperature for each stage of a cannabis plant’s life. For a plant to develop and thrive many different processes need to happen. Each of these processes has an optimal temperature. This article is the second in a 3-part series exploring the optimal growing temperatures for cannabis. In Part 1, we looked at what growing temperatures are often used by experienced cultivators. We found that there was little consensus among expert growers on the ideal temperature for growing cannabis. In Part 2, we’ll look at temperature from a life history perspective by observing the growing temperatures for cannabis in its native environment. Here is a full overview of the series, if you missed something:

What is Cannabis' Native Growing Environment?

First, it’s important to establish what is the native environment of cannabis? There are many resources that cover this topic. A book by Clarke and Merlin (2013) titled “Cannabis: Evolution and Ethnobotany” does a good job of summarizing and sorting through the available data. Here’s an excerpt:

“Even though the arguments for hemp being endemic to Central Asia are not conclusive and, in fact, the origin and first use of C. sativa and C. indica may have occurred elsewhere, we suggest […] that the natural origin of Cannabis took place in Central Asia, possibly in the upland valleys of the Tian Shan or Altai Mountains”

Below is a map of the hypothesized native growing range for cannabis (Figure 1). It shows the upland valleys of the Tian Shan and the Altai Mountains.

Figure 1: Hypothesized native growing range of the cannabis species. Modified from Clarke and Merlin (2013).

What are the Growing Temperatures in Cannabis' Native Environment?

I chose several sites along the border of this range and looked up temperature data for each site. I used temperature data collected from NASA satellites, which collects daily weather data every two weeks. I chose weather data from the year 2001, as this was the earliest year that data was available. Ideally, we would look at temperature data from the time when cannabis first emerged on the Earth – in 5000 BCE, but this is obviously not possible (Clarke and Merlin 2013).

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Figure 2: Seasonal day temperatures in the highlighted region of the map.
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Figure 3: Seasonal night temperatures in the highlighted region of the map.

At the beginning of the season in May and June, wild cannabis seeds germinate (Clarke and Merlin 2013). At this time they experience daytime temperatures of about 26°C (Figure 2) and night temperatures of about 12°C (Figure 3). During the vegetative stage which occurs in early summer, temperatures average 30°C during the day and 14°C at night. Cannabis blooms from mid to late summer, when temperatures drop from about 30°C down to about 22°C during the day. At night, late summer temperatures hover around 12-7°C. A downloadable infographic of the average temperatures is seen to the right and can be downloaded as a PDF.