I’m a grow monk. For the past 25 years, my main passion has been growing cannabis every day of the year. Because I do that, I haven’t been able to create a social life, romance, marriage, kids, or many hobbies. I spend almost all my waking hours nurturing and studying my cannabis plants. Doing that, I’ve learned intuitive and objective ways to know my plants are happy and healthy. Today, I’m sharing one of those ways with you…

Cannabis scent is one of the main reasons I grow marijuana. I absolutely love the dozens of scents cannabis creates. It’s not just the buds either. With some strains, cannabis scent is powerfully present in seedlings less than two weeks old.

I used to believe cannabis scent was almost entirely determined by genetics, time of day, and growth phase, with a little influence from environmental conditions and cultivation inputs (water, nutrients, C02, light). But as I studied my plants, keeping careful records of what time of day they created scent and when scent was absent, and what if anything correlated to scent, I realized the presence of scent was an indicator of plant health and happiness. I also realized that environmental conditions and cultivation inputs had a far bigger influence on scent that I’d previously assumed.

For example, you’ve probably noticed that when you give nutrients water to bloom phase fat-bud plants that had an overly dry root zone, the plants gave off a burst of scent as the water entered the roots. To my bewilderment, on other occasions I noticed that when I watered my plant, their intense bud scent suddenly disappeared. These two effects puzzled me, as they seemed to contradict each other. In one case, nutrients water stimulated scent, in the other, it depressed it.

Another cannabis scent story….

When I first started replacing my high intensity discharge (HID) metal halide and high pressure sodium bulbs and ballasts with professional LED grow lights made for cannabis, I knew I was delivering a lot more photosynthetically active radiation (PAR) to my plants than before. I didn’t expect more scent from my plants because of switching to LEDs, but during a side by side test using identical clone plants in peak bloom phase, the plants growing under the LED grow lights put out a lot more scent than the plants growing under HID grow lights. Using professional PAR meters, I saw that the HID lights were delivering 20-35% less PAR than the LED grow lights.

If I turned up the PAR intensity on my LED grow lights, the same buds that had been sending out a cloud of scent stopped doing it. When I reduced the intensity, the scent came back. I’m still doing observations and measurements of PAR and its effect on scent, but I’ve now concluded that each strain and plant has a narrow optimal range of PAR intensity it can handle. When I’m delivering the correct amount of photons, the plants are happy, and generate lots of scent. If I underdeliver or overdeliver photons, the plants aren’t happy, and their scent intensity drops. I’ve also noticed that certain brands of grow lights stimulate terpenoid scent more. The Lush Lighting Dominator appears to have one of the best spectrums for stimulating cannabis scent.

Grow room temperature, relative humidity and vapor pressure deficit also influence the amount of scent coming off my plants.

If I go into my grow rooms during peak bloom lights-on, and there’s no wonderful marijuana odor scent pervading the air, I get worried. Lack of scent may indicate something’s wrong in the environment. It could be something in my climate control system is broken or set wrong, creating unfavorable environmental conditions that shuts down photosynthesis.

Lack of scent leads me to investigation, and this may reveal problems including my C02 delivery isn’t working properly, the circuit for my dehumidifier has shut down, irrigation pumps have failed, nutrients water pH has failed, etc.

Lack of cannabis scent, especially during peak bloom with strains I’ve grown before and known as strong-scent strains, forces me to implement my grow op emergency checklist that includes checking all grow room factors and plant inputs under my control. I also physically examine the plants.

On one occasion, when buds that had smelled strongly of skunk and diesel fuel suddenly lost all scent for several days, I discovered that mealybugs were hidden away at the bottom of the main stalk. They were sapping the plants’ strength; the lack of scent was a symptom of this damage.

I removed the mealybugs, fed my plants an iron and Vitamin B recovery formula, sprayed them with botanical anti-pest compounds. Three days later, the scent returned, and continued until harvest day.

My marijuana plant studies show me that cannabis plants have a natural cycle related to scent. In the artificial environment of an indoor grow room, that natural cycle might not be so natural, but I’ve noticed that even when all conditions and inputs are perfect, there are times during lights on and lights off cycle when scent levels go up and down drastically, with no influence from environment or cultivation inputs.

Plant scientists tell me this has to do with photosynthesis mechanics during lights-on cycle, restoration and other metabolism happening primarily during lights-off cycle, and other natural rhythms that plants have independent of anything we as growers are doing for them. I have to be aware of the natural ebb and flow of scent production as a background pattern when I’m making decisions about how alarmed to be if scent has suddenly disappeared from plants that are usually very stinky.

So how can you bring this information into your marijuana growing so it benefits you and your plants? The first thing to do is get to know your strains intimately. Some cannabis strains don’t generate much scent. Most do. Cannabis strains with significant amounts of Skunk, Haze, Diesel, and Chem genetics in their breeding lineage are almost certainly going to generate lots of scent starting in early bloom and especially in the last 50% of bloom phase–but only if they’re healthy and happy. Contact the seed breeder and ask them about scent for the strains you grow.

Keep a grower diary that records every detail of your grow op several times during each lights-on cycle. There are automated grow room data-logging systems you can use for technical details. But your nose is the system you use to gauge scent intensity and flavors. Be sure to record what your nose tells you. This will help you determine the background natural ebb and flow of scent in your strains.

Over time, if you focus on becoming very familiar with the natural scent rhythms of your strains, you’ll be able to differentiate between them versus scent variations that come from environmental conditions and plant inputs.

Watch carefully to see which if any input actions and environmental conditions acutely and immediately correspond to increased or decreased scent output. Along with what I described before, that watering dry plants immediately produced a burst of scent, I also noticed that an hour or two after watering with molasses added to the nutrients solution my plants would generate a wicked amount of scent, and this didn’t happen minus the molasses.

This is the intersection of intuition, art, and science in growing marijuana. It’ll probably be a long time if ever before scientists discover all there is to know about why cannabis plants produce scent, what scent compounds do for us medically and/or psychoactively, and how scent is tied to plant health and vigor.

That’s fantastic. It means that we growers are the pioneers of cannabis scent. So if you’re growing premium cannabis strains known for potent scent but especially during peak bloom you’re getting little to no scent from them, it’s useful to investigate whether grow room conditions and/or inputs are out of range in your marijuana grow op, and adjust them to optimum as soon as possible.

One other thing: your nose can often tell you when gray mold (bud rot) and other problems are festering on your plants or in your marijuana root zone, hydroponics reservoir and elsewhere.

If your grow op doesn’t smell like cannabis resins, but instead smells like ammonia, mold, rot, decay, wetness, your nose is telling you to check for pathogens such as gray mold, root root, and other problems. A properly tuned indoor cannabis grow room can smell like a pure summer day in the wilderness, perfumed by the many delicious scents cannabis exudes when it’s happy and healthy.