If your basic conditions are all correct, you should already be achieving good levels of terpenes in your harvest. But there are a few extra steps you can take to maximize your terpenes even more. Let’s take a look at some of them.

Water Stress

In our first post on terpenes, we briefly mentioned stressing the plants by pruning, and keeping humidity very low – but how else can you stress your plants to produce more terpenes?

We can reduce humidity directly by either raising grow room temps or by using a dehumidifier. But we can also reduce the amount of water we feed the plants! Doing this will contribute to lower overall humidity, and will also cause the roots to grow deeper and longer in search of water.

This controlled stress is used in grape cultivation for wine, and winemakers believe that it causes richer, deeper flavors as the roots take better advantage of the compounds available in the soil. It’s a tricky balance – if roots get too dry, the plant will wilt or even die. But get it right, and your plants could get a significant boost in terpene and cannabinoid production.

Tweaking Light Spectrum

Certain types of lighting may cause terpene production to be higher. Particularly, certain high-quality LEDs are becoming associated with higher terpene production. This is partly explained by the fact that LED lighting can lead to cooler temperatures in the grow room. Hot forms of lighting such as HPS can make grow room temperatures very high, requiring expensive air-conditioning to cool the air.

It’s also possible to tweak some LED lighting systems to manipulate the spectrum of light that the plant receives. If you tweak the balance of red and blue light in the right way, it may actually help you to maximize your terpenes too.

There are only one or two studies on the subject of LED light spectrum and terpene production, so there’s still a lot of doubt on the topic. One study showed that a red-blue ratio of 80:20 was better for terpene production than a ratio of 60:40. But that study was on chrysanthemums, and it also looked at the effects of different CO2 levels.

At least one LED maker suggests switching the ratio of red to blue light from 80:20 to 70:30 or even 60:40 during the last two weeks of flower, to allow the blue light to maximize your terpenes.

“No-Red” Light Treatment

Another study conducted by a manufacturer of LED lights found something potentially very interesting to LED users. Lumigrow found that giving cannabis plants a “no-red” light treatment for the last three days of flowering could “increase terpene levels in Cannabis for most strains studied”. The strains studied were Chocolope, J1, OG18, and Reserva.

(Note: we emailed Lumigrow to find out more – they told us that they’ve “discontinued the Cannabis Spectral Guide for the time being as we rebrand and improve upon it”. We’re going to talk with them to find out more – we’ll update when that happens.)

Another possibility to consider is using LED lighting that also contains UV-emitting diodes, or to supplement your HPS or other lights with a UV addition. UV light has been shown to boost production of essential oils in various plants – although again, there’s not a lot of research out there yet.

Manipulating the Twilight Period

Tweaking light spectrum and intensity at certain times may be one of the most advanced ways to boost terpene production. Researchers have shown certain light-sensitive pigments are crucial to various growth processes. The pigments require specific wavelengths of light to activate these processes, such as those found during the twilight periods.

Twilight occurs in stages and gets gradually more “blue” as it fades to total darkness. The earliest stage of twilight after dusk is redder. Later stages of twilight are characterized by predominantly blue light and far-red light, and by low light intensity. Dusk/dawn and twilight periods vary according to the angle of the sun’s rays hitting the earth, and their length is very different at different latitudes.

Recreating the twilight period by fine-tuning LED lights could provide yet another way to maximize your terpenes. If you want to get really in-depth, you can even try to imitate the twilight period of the geographical region your plant originates from! Particularly if you’re growing a landrace, you could use its original latitude to work out twilight duration. A hybrid is a little more difficult as it may have parents from different latitudes, but may still benefit from a rough average twilight period.

Twilight and Latitude

On the equator, the twilight period is around 20-23 minutes, with little-to-no seasonal variation. At 32N (the latitude of Himachal Pradesh, India), it’s around 29 minutes at the summer solstice and 24 minutes at the autumn equinox. At 53N (northern Kazakhstan, where ruderalis-type cannabis grows), twilight is 55 minutes at the summer solstice and 35 minutes at the autumn equinox. To find out exact durations for your latitude, use this tool.

At key times of the year, such as late flowering, twilight could be an important factor that most indoor growers disregard entirely. We still have a lot to learn about how exactly our existing knowledge applies to cannabis – but it’s worth experimenting! Gradually shift from predominantly red to a mix of blue and far-red before total darkness, while also gradually dimming the overall intensity.

Experiment with longer twilight periods during growth, and a short period at the start of flowering (the shortest twilight time is at the equinox – when the light cycle naturally drops to 12/12). Allow your twilight period to get gradually longer towards the end of flowering.

Root Zone Tweaks

Maintaining a healthy root zone is of critical importance. Following the basic steps outlined above will ensure that your terpene production is good and healthy – but what tweaks can you try to maximize your terpenes even more?

First off, you can experiment with the addition of sugars to the root zone, as many growers do as standard. Some argue that sugars provide a direct boost to photosynthetic processes as the roots absorb them. But the jury is still out on whether cannabis plants even absorb sugars directly through the roots! Many plant species do not, although some others apparently do.

Others argue that it’s not even about absorption through the roots. When you feed sugars to the root zone, the bacteria and fungi living in the soil feed on it. When you provide your soil microbes plenty of sugar to feed on, their populations grow and thrive. They become more easily able to process nutrients into forms more easily absorbed by the plants.

Microbes That Boost Terpenes

Some of these microbes may be particularly useful in boosting your terpene production. A 2015 study on tomatoes pointed towards Rhizophagus intraradices, a mycorrhizal fungus, and Beauveria bassiana, a pesticidal fungus. Soil inoculation with these two microbes, either alone or in combination, led to enhanced levels of monoterpenes and sesquiterpenes. In fact, there were even new monoterpenes that were not present in the control plants.

There are various commercial sugar and carbohydrate blends, but many growers simply add blackstrap molasses to their water. Make sure you dissolve it in some lukewarm water before adding it to your feed, as it won’t mix in properly otherwise. You can feed with molasses every week or so, starting right at the beginning of the vegetative period. This will give your micro-organisms a nice early boost. You can continue feeding with molasses until the very end of flowering, including the flush period.

Note: you should be careful when adding sugars to the root zone. If sugar concentration is too high, it may interfere with the roots’ ability to absorb water and nutrients. It’s not clear what exactly is “too high”, but most growers stick to around 1-2ml of molasses per liter of water, with good results.

Compost Tea & Soil Additives

Compost tea is another great way to enrich your soil with a complex blend of microorganisms, enzymes, and micronutrients. It often contains molasses, which encourages the bacteria present to thrive and reproduce. There are various commercial blends available, including Veganic Special Sauce from OG Tea (which uses no animal-derived products!), but many gardeners love to make their own compost tea. Look out for our upcoming guide on how to make it yourself!

Another interesting product is Soil Balance Pro, a blend of microbes designed to deliver nutrients more effectively and maximize your terpenes. Their website claims 150-500% increases in terpenes, using a blend of 62 root-dwelling microbes. Common strains of Bacillus, Trichoderma, and mycorrhizae make up some of these. Proprietary strains isolated from living cannabis roots make up the rest. The blend also contains humic and fulvic particles and a range of micronutrients. It’s apparently for hydroponic substrates, which are often lacking in microbes at the root zone. We haven’t tried it yet, but we’d like to!

Nutrient Tweaks

There are various commercial “terpene enhancers” out there, although many of them are just sugar blends you can reproduce yourself. Take a good look at what’s inside and do your research before opting for one of these products!

One product that goes beyond the usual blend of sugars is Terpenez by Solis Tek. It’s a blend of “natural precursors coupled with organic, bio-identical, plant derived terpenes”. So it basically feeds terpenes to the plant, along with some undisclosed compounds that apparently boost natural terpene production. We’re not sure, but we would certainly like to give it a try!

On the other hand, there are various individual hacks you can use to tweak particular nutrients and maximize your terpenes. One possibility is increasing sulfur levels during flowering. Sulfur compounds can be very stinky and are a big contributor to the smell of garlic. But it’s not actually clear if sulfur has much (if any) connection to terpenes themselves. Molasses contains some sulfur, so if there is a connection it may partly explain why molasses can boost terpene production.

Another possible nutrient tweak is increasing calcium – another nutrient contained in blackstrap molasses, which is convenient! One study shows that calcium is highly associated with terpene production in chrysanthemum plants. Calcium is very important to the complex processes that manage pest defense in many plants. As we know, terpenes have a fundamental role in pest defense!

So if you follow these steps, you should maximize your terpenes at every harvest! Let us know what you think of this advice – have we missed anything? Have we got anything straight up wrong? Tell us all about it in the comments.