Everything you wanted to know about terpenes as a cannabis grower. Learn what they are, how to increase them, and most importantly, how to keep them once you’ve got them.
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What Are Terpenes?
Terpenes are volatile unsaturated hydrocarbons found predominantly in plants, contributing heavily to their aroma. While cannabis is well known for its heavy production and range of terpenes, conifers like pine trees are rich with terpenes as well. Perhaps, not surprising to those who have noticed cannabis often has a piney smell, with both producing the terpenes α-pinene, β-pinene, camphene, and limonene, among others.
Where once, interest in terpenes was mostly due to their aroma, which enriches our enjoyment of cannabis, today, interest is in their medical benefits and how they influence the overall effects of consuming cannabis. While THC is still most marijuana users’ favorite cannabinoid, many of us don’t love it by itself due to its uneven and intense effects. But add some terpenoids in there with that THC, and baby, you got a euphoric and pleasant stew going.
Like the cannabinoids in cannabis, we find the majority of terpenes these plants produce within their trichomes. There are three different types of trichomes based on size and location that cannabis produces: Bulbous, Capitate-Sessile, and Capitate-Stalked. Capitate-Stalked trichomes produce the highest quantity of desirable cannabinoids and terpenes and are easily the most viable so the naked eye.
Our crops produce terpenes to help attract pollinators, for defense against pests and diseases, and on.
Terpenes Vs. Terpenoids?
Often mistakenly used interchangeably, there is a difference between terpenes and terpenoids. To stay simple, terpenoids are simply terpenes that have oxidized, which mostly occurs during the drying and curing process. This means you’re technically consuming terpenoids, kind of similar to how you consume THC and not THCa.
Types of Terpenes
Within the terpenes, we can break them down into groups based on their final structure. How many isoprene units a terpene has will tell you its type. One isoprene unit is composed of five carbon atoms.
With only 2 isoprene units made up of 10 carbon atoms, our “simplest” terpene is perhaps also one of our favorites, with popular terpenes pinene, myrcene, and limonene all belonging to this group. Other notable monoterpenes include nerol, cetrol, camphor, and menthol.
Composed of three isoprene units, sesquiterpenes include nerolidol and farnesol. The most common terpene in this group this the notable terpene, β-caryophyllene.
Like monoterpenes, concentrations of sesquiterpenes flux as the plant ages, appearing higher in late veg, then reducing in early flower before significantly increasing again. However, unlike monoterpenes, sesquiterpene levels remain stable after about three weeks into flowering.
Composed of two monoterpene subunits, or four isoprene units, phytol is probably the most notable diterpene.
With six isoprene units, not all terpenes come from the flowers or even the trichomes on the leaves and stems. The triterpenes friedelin and epifriedelanol, which are found in the roots of cannabis plants, are two of those. Like the terpenes found in the flowers, terpenes from the roots appear to have similar health benefits, which include anti-inflammatory, antioxidant, estrogenic, anti-cancer, and liver protectant properties.
Most Common Terpenes In Cannabis
There are more than 400 unique terpenes identified in cannabis, but we don’t know the effects of most of them. Thankfully, we can still learn a lot about terpenes by looking at just a handful.
Primary Terpenes Found In Cannabis
Primary terpenes contribute the most to the aroma, while additionally having prominent effects on the body and synergistic properties that promote the entourage effect. Many terpenes fall into this group, so let’s just look at the six most common.
This monoterpene is found heavily in pine needles, basil, rosemary, and, of course, cannabis. It’s the most common terpene found in plants around the world. With a piney aroma and beneficial properties that may help with inflammation, constricted airways, anxiety, and pain, pinene appear to help combat short-term memory impairment associated with THC.
With an earthy, woody, and spicy aroma, cannabis strains with lots of humulene — like Gelato — go great with hoppy beers, thanks to them sharing humulene. A sesquiterpene, humulene once was often mistaken for the terpene, β-caryophyllene. Sharing the same chemical formula, these closely related terpenes are often found together, both producing similar anti-inflammatory properties.
Almost identical to the terpene humulene, the most fascinating thing about β-caryophyllene, is it’s the only terpene known to bind to CB2 receptors.
Like other terpenes, the name often gives away what aroma it produces, thanks to its association with another crop. Found in citrus fruits such as lemons, the monoterpene limonene promotes calm, an elevated mood, and healthy digestion.
First, the cannabinoid CBD was associated with the classic “calming” effect known as “couch-lock”, then it was CBN, but now, it looks like the monoterpene myrcene plays an important role as well. Found in plants like mangos, thyme, and lemongrass, myrcene is the most common terpene in commercial cannabis strains, representing 20% of the terpene profile in modern commercial strains, according to Leafy Labs. In some strains, myrcene makes up as much as 65% of the total terpene profile in them.
With a lavender scent amped up with mild spiciness, linalool’s aroma alone is said to help bring calm and relaxation to the mind. Found in over 200 plants like lavender, linalool plays an important role in keeping our crops healthy, thanks to its antimicrobial properties.
Secondary Terpenes Found in Cannabis
While they are not as abundant as the primary terpenes and don’t contribute heavily to the aroma, secondary terpenes are incredibly synergistic with the primary terpenes and cannabinoids, leading many to consider them essential for promoting the most optimal entourage effect.
A diterpene that is a degradation product of chlorophyll, phytol is found in pretty much every cannabis strain. Consuming this terpene increases the expression of the neurotransmitter, GABA, which produces relaxing effects.
A monoterpene, eucalyptol is sometimes referred to as “cineol”. With the potential to help with sinus and nasal congestion, this minty-smelling terpene is commonly found in eucalyptus, bay leaves, cardamom, and sage.
Peppery and citrusy, sabinene is found in some oak trees, black pepper, carrot seeds, and cardamom. While only appearing in small amounts in cannabis, there is interest in sabinene’s anti-inflammatory and antimicrobial benefits.
Proven Ways To Increase Terpenes
Below, we are going to discuss proven-but-not-essential methods gardeners can implement when looking to increase their crops’ terpene production.
However, the most important factor for high terpene production is mastering the essentials. That means providing appropriate light levels, proper fertilizer/irrigation, management over temperatures, nutrient issues, and other environmental factors, and selecting good genetics.
1. Every leaf Gets Light
With research finding that the concentration of trichomes decreases top-down due to poor light penetration, ensuring most of our crop’s leaves are getting near equal light is critical.
Adding lights that run along the side of our crops while training the plants themselves to grow horizontally instead of vertically are a gardener’s best friends for this. Mild defoliating may help as well, but a greater focus should be on getting light on all the leaves for optimal results. A leaf gone is one less solar panel for capturing light.
2. Stress Can Be Good
Did you know that pests like mites can increase your terpene production? Thanks to biotic/herbivore stress affecting terpene production, it is true!
Now, while most of us want greater terpene production, we probably are gunning to release a bunch of mites into our gardens. Fortunately, there are other preferable ways we can stress our crops, from drought to light stress with UV light.
There is one caveat with stress methods that use drought, heat, and insects. They should be seen as terpene and cannabinoid profile manipulators and not production increasers, because while they do increase some terpenes, they reduce others. For example, seven days of drought stress decreased CBD and THC accumulation by (70–80%) while increasing CBG by 40%.
Results are mixed when it comes to mechanical stress, but it appears mild mechanical stress practices such as low-stress training, and even topping, are unlikely to hinder terpene production when utilized at the appropriate times. As seen above, even if they aren’t directly increasing terpene production, they open the plant to more light and better growth, which will.
3. Redirecting Energy With Light
Without a doubt, the biggest factor in growing amazing cannabis crops full of terpenes is by giving them the optimal amount of light (photons) they need. Not far behind, however, is the type of light spectrum you give them.
While red and blue lights are the best spectrums for driving photosynthesis, yellow, green, and on are critical for optimal growth. In fact, while a blue-heavy light spectrum helps direct energy into vegetative growth and secondary metabolite production, whereas red directs energy to flower production, the UV spectrum may be the key to pushing terpene production to new heights.
UVA and UVB light, especially UVA, are gentle ways to stress our crops, forcing them to redirect some of their energy into repairing and protecting themselves, which they create terpenes and cannabinoids to help with. Again, there is one little issue.
A 2017 study found that just 48hr of UVB light causes a threefold accumulation of the sesquiterpene α-farnesene. Awesome, right! Well, maybe no, as it causes similar terpene-loss issues seen with other stress methods, decreasing linalool by 60%. While this study was on peach fruits, meaning we may see different terpenes affected when applied to cannabis, it’s still likely we’ll see some terpenes increase while others decrease.
Tricky indeed, but ultimately great for those looking to increase or manipulate their terpene ratio to better achieve certain benefits or aromas. And unlike biotic, drought, heat, and mechanical stress, correct applications of UV-stress, especially from UVA light, appears to result in a net positive. And it is something even home growers can start experimenting with now. Plus, it’s more likely than not that we would see an increase in cannabinoids like THC with UV, which definitely offsets the loss of certain terpenes.
May Improve Terpene Production
While the methods above go far in promoting terpene production, as you’re about to see, that’s only half the battle. Retaining the trichomes our crops have already created may be just as important, if not more so, and these methods largely make up our next section.
1. Adding Silica
While not an essential mineral for plants, silica is very beneficial, strengthening their cell wells against pests and diseases, in particular, powdery mildew. According to research out of Utah State University, cannabis trichomes that house our terpenes are made up mostly of silica and our grow media can be set up to supply our plants with it.
While it appears silica will not directly increase terpene production, it does protect them by strengthening the trichomes from degrading, along with helping them stay on the plant better.
2. Proper Dry and Cure
Just like with silica, which strengthens our fragile trichomes and protects our terpenes, a proper dry and cure are just as important. Slow and steady are still the keys to nabbing the best dry and cure. You’ll need high humidity and very little airflow for that, so make sure to watch for powdery mildew. 5-14 days for drying and 14-21 days for curing are the current recommendations.
3. 24 hrs light Before Harvest
This is a fun one sure to cause controversy.
Next time, instead of giving your cannabis plants 48hrs of darkness before harvest, run your lights for a full 24hr before harvesting. Terpene and trichomes production in cannabis happens when the lights are on. In fact, when the lights are off, sugars like sucrose leave the trichomes, but we don’t want that, as these sugars help create trichomes and secondary metabolites like terpenes. In other words, when it’s dark, our plants no longer have all their resources to create new trichomes or terpenes.
It’s an extreme method and not the best tested — not that those things stop many cannabis growers — and the grower themselves will need to weigh whether the potential increase in trichomes is warranted over the lack of reproductive development.
But if you do an extended dark period before harvest, you’ve already excepted the “trade-off”. So you own it to yourself to try this method out. It’s just 24hrs of light before the chop, so we don’t have to worry about our crops trying to revert to the vegetative stage, and when timed correctly, reproduction development is fairly slow at this point. Just make sure to watch for excessive heat with your lights being on for so long.
4. Plant Sweeteners And Other Biostimulants
We just talk about how sugars play a big role in creating terpenes, so in theory, giving our plants more sugar means they can make more terpene? Appears likely, but not in the way one may think.
While plants can’t absorb added sugar — they make their own through internal metabolic processes — we may be able to simulate them into synthesizing more sugar. Adding sugar to soil and hydroponic media like peat moss can also feed beneficial microbes, which improve our crops’ ability to uptake nutrients used to create new terpenes. Mastering your grow media is vital to terpene production, as you’ll read later.
Fertilizers that contain biostimulants such as protein hydrolysate, humic acid, and seaweed fall into this category as well.
5. Keep Things Cool But Not Too Cool
Terpenes and excessive heat don’t get along, and temperatures above the optimal range will result in them degrading, while temperatures below stunt photosynthetic rate. While leaf temperature is the more important factor than the air temperature, when properly watered, the difference between the two is usually within just 3 degrees Fahrenheit.
But that is not all! What we really need to look at is flower bud temperature. Where leaf surface temp is usually lower than the air, the flower buds — especially near harvest — can be 5 degrees higher than the air temperature because their size and density let them build up a lot of heat.
With flower bud temperatures being higher than air temperatures while leaf surface temperatures are lower, it is likely safe for most of us to just monitor our air temperature — which is nice because it’s the easiest. This gives us an optimal temperature range that’s between 72-77°F (22.2-25°C), with 70-80°F (21-26.7°C) being a fairly safe general range that is easier to stick to.
As you approach harvest, you may find it’s worth the extra work to get into the optimal range. Then, for the last days leading up to harvest, you may even want your temperatures to be in the mid-to-upper-60s°F (18-20.5°C), according to Christine DeJesus, director of cultivation at Galenas in Akron, Ohio.
The ranges above apply to non-CO2 supplemented grow rooms. When implementing extra CO2, you likely want your room to be 5-10 degrees Fahrenheit hotter than a grow room without supplemental CO2.
Unlikely or Unproven Ways To Increase Terpene Production
1. 48hr darkness
Looking to reduce trichome production? That’s easy! Just cut off your plants’ energy by turning off the lights.
As we saw with 24hrs light, terpene and trichome production comes to a halt when the lights are off. Hitherto, I’ve taken a middle ground on 48hr darkness before harvest. I don’t do it but have conceded that something wonky may be going on that makes this gardening method work for some.
Today, I’m taking my stance against the matter because I believe it’s hurting trichome and terpene production due to sugar loss. It’s appearing likely that the reason 48hr darkness before harvest helps some is that it reduces high temperatures that were deteriorating terpenes — which can happen when air temperatures surpass 80°F (26.7°C).
2. One Grow Medium To Rule Them All
There is no doubt that our growing media has a significant effect on terpene production. But what media is truly the best is right now hard to say, and that’s why it’s in this section.
It’s often claimed that cannabis crops grown in soil and hydroponic soilless media like peat moss have higher levels of terpenes, in large part thanks to the microbial community. And this may be true, but with some research finding tomatoes grown in deep water culture systems (DWC) produce higher levels of the terpenes lycopene and β-carotene, the debate gets messy. Let’s make it messier!
When studying two C. sativa cultivators, Brandon Yep and his colleagues found that while the hydroponic peat-based media top-fed with synthetic produce 42–116% greater inflorescence biomass, the crops in the aquaponic media had greater levels of Δ9-tetrahydrocannabinolic acid (THCA), cannabidiolic acid (CBDA), and the terpenes ß-pinene and limonene.
Right now, your best bet is probably picking the media you prefer (within reason) and learning all its unique quirks and how they affect plant growth. They all have their pros and cons.
Flushing Before Harvest
You can’t create something out of nothing, so flushing, which removes essential building blocks for building trichomes, should cause you to question it.
Properly feeding your crops so you’re not forced to flush before harvest is very likely to result in higher terpene production, thanks to it keeping our crops healthier throughout their life. We don’t have a lot of studies on flushing, but the rare few we do have yet to find flushing helps when crops are fed properly.
As we’ve seen, there are many things we can do to increase and keep our trichomes/terpenes safely on our buds.
But before you get into light spectrum manipulation and dowsing your crops in hopeful biostimulants, you want to nail down all the basics. From correctly fertilizing your plants to keeping them in a happy and healthy temperature and humidity range, these basic factors are going to play the largest part in terpene and trichome production. But from too high fertilizer formulas with incorrect NPKs to suppositious growing practices, many of us have yet to master the basics of cannabis gardening yet.
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