Terpenes are complex organic molecules that are produced by an abundance of organisms. In plants specifically, they play a vital role in growth and development by attracting pollinators, repelling predators and preventing disease.

“Terpenes are volatile organic compounds (VOCs), which means that they’re airborne, and [will] dissolve into the air and travel pretty great distances,” said Shaye Donald, a horticulturist in the professional technical services team at Hawthorne Gardening Company. “[This] is important for plants because they don’t get the luxury of moving around. … They’re very costly molecules for the plant to produce, … [and] they’re very energy-dense molecules, so it takes a lot of energy to produce them.”

Donald breaks down the critical role terpenes play in a plant’s environment and development and describes how Hawthorne’s Terpinator plant nutrient product is designed to help improve terpene concentration in plants.

Cannabis Business Times: Why do plants produce terpenes?

Shaye Donald: Plants produce terpenes for a wide variety of different reasons. One of the main purposes that plants create terpenes is in response to different types of stress. A big one is to deter or even poison pests. If pests such as insects are exposed to terpenes, they [can] get repelled or even die. Products containing terpenes have been used in many different pesticides, [such as] those based on essential oils. Essential oils are loaded with terpenes, which is the primary reason they smell so much.

Terpenes also are beneficial to plants when it comes to other biotic stressors like pathogens. Similar to pest prevention, certain terpenes will inhibit the growth or establishment of disease-causing organisms. 

Terpenes are also critical for abiotic stress responses. This means stressors like too much light, too much heat, lack of water, things like that. One reason the plant produces these is to signal an immune response.

In all these cases, [terpenes] are critical for plant-to-plant communication. Cells of the plant will pick up when there’s a terpene present, and depending on the terpene, it will elicit a response. So, [for example,] if a pest is chewing on the top of a plant, the terpenes that are produced by the leaf being chewed on might [send a signal to the] other leaves and warn the leaves like ‘Hey, there’s something chewing on me, you better toughen up now before this thing comes to chew on you.’

CBT: Could you describe any relationships between plants and other species that incorporate terpenes?

SD: There are a number of really interesting responses from plants where terpenes are involved in signaling other species. When chemicals are produced by an organism for interspecies communication, they are known as semiochemicals. Many of the terpenes that plants produce can be classified as semiochemicals.

One of my favorite examples is if a caterpillar is chewing on a leaf. The leaf’s cells will interact with the saliva and produce specific terpenes that then disperse into the surrounding environment. A number of parasitic wasps have evolved to be attracted to specific combinations of terpenes that plants put off. So, it’s a way for the plant to signal the wasps to say, ‘Hey, there’s a meal here.’ So, both species benefit from this interaction. The only one who gets the short end in this is the caterpillar. 

What is really cool is that if the same leaf is cut by a knife, the terpenes released would be different than when the caterpillar munches on it. This means it is a species-specific response, and in some cases, even the wasp or other predator is attracted only if that mix of terpenes is produced.

So, the point is that the terpenes are used as a way to communicate between different species as well as all the other things they do. So, the plant kind of puts out a signal, and the wasps that are predators of those pests will detect this and show up to save the day.

CBT: How does Hawthorne’s Terpinator nutrient solution work? Can you provide a brief overview of the science behind it?

SD: As I mentioned before, terpenes are very energy-dense molecules. They require a lot of different elemental building blocks to be produced. It’s essential for growers to make sure that they have the correct ratio of different nutrients, such as nitrogen, calcium, phosphorus, potassium and so forth. If [the plant] was lacking in any individual elements, it’s not going to be possible to produce as many terpenes. That’s where Terpinator comes in and gives the grower the ability to change the ratio of different nutrients to ensure that they have the correct amount of [each one].

CBT: Do specific nutrients correspond to specific terpenes’ development?

SD: Phosphorus is going to be a critical one because of its role in energy transport as a component of ATP, which is adenosine triphosphate. There’s sulfur, which is critical for creating energy-rich building blocks. … Nitrogen is also important for amino acids, proteins and the metabolic process. Potassium is essential for keeping the stomata open, and that is critical to allow carbon dioxide into the plant, which is important for photosynthesis. Carbon is the building block for all terpene carbon chains as well as hydrogen, but those both come from the air and water, respectively.

Essentially, every nutrient is going to be important for producing terpenes because they are all necessary for growth and photosynthesis to occur. If something is lacking, then it’s probably going to be disrupting a process that either directly or indirectly supports terpene production in the plant.

CBT: Why do terpenes smell at all?

SD: I think that’s an interesting thing. Why would the plant want to produce these terpenes? … When a plant initially starts to produce [terpenes], maybe it was for a pest repellent or a pathogen repellent. Whatever it originally was, it now can use terpenes to have relationships with other species, and I think that’s one of the most important benefits for plants.

So, just by smelling these plants and enjoying that smell, [humans] are now protecting those plants and putting a lot of energy into making sure that they survive. We prize, protect and cultivate them, much in the same way as that wasp is protecting the plant. I think humans have evolved with these plants like the wasp and plants have. It’s a mutualistic relationship between humans and terpene-producing plants; We’re not the only ones getting something out of it. 

I think the plant is now, by artificial selection, being pushed to produce more and more [terpenes] because the ones that [make] more tend to be prized. Once they are prized, they are spread by people all across the globe, where they wouldn’t otherwise grow. I would argue that plants are getting huge evolutionary benefits because of these terpenes and the fact that people like how they smell.