Visual Trichome Evaluation to Determine Peak Harvest Time

Visual Trichome Evaluation to Determine Peak Harvest Time
Professor DeBacco

Why Look at the Trichomes?
Trichomes provide an indication of the plants ripeness and cannabinoid and terpen concentrations.
Visual evaluations may not provide an exact number, it can indicate when the greatest concentrations of these compounds are likely to occur in the plant.
A plant sample chemically analyzed is the “best” method, this is time consuming and costly so out of reach by most growers. So, the visual inspection can get very close to peak harvest with minimal cost helping growers maximize their production.

Different Types of Trichomes
Bulbous
Smallest (20 micrometers) and need an aid to be seen
Can synthesize cannabinoids and terpenes
Swell in size as they fill with oil
Sessile
Larger than bulbous (75 micrometers) but still hard to see with the naked eye
Develop early 3-week old plants
Stalked
Very large (500 micrometers) and can be seen with the naked eye
The ‘prized’ trichomes that appear during flowering
Most likely to get damaged

What We Are Looking At…
(A) An individual inflorescence, with majority of the organs covered in stalked glandular trichomes.
Arrow indicates cluster of calyces and bracts covered with trichomes.
(B) Dark field micrograph of stalked glandular trichomes protruding from calyx epidermis. Biosynthesis of secondary metabolites occurs in the secretory disk cells lining the base of the globular trichome head. The metabolites are stored in the clear subcuticular cavity above the secretory disk cells; this cavity will turn milky white to dark brown over the course of flower maturity.
(C) Graphic illustration of stalked glandular trichome structure
Color Differences of Trichomes
Clear- “Empty” not ready for harvest
Cloudy- Increased levels of cannabinoids and terpens
Amber- “Converting” in this stage desirable compounds may be changing to less desirable compounds

Can Pistils be Used?
Pistils can provide a quick guide, but it is the trichomes where the cannabinoids and terpenes are stored so this is the plant part that should be observed with attention to detail.
Traditional Method
Loupe
Works great and still recommended, but it is hard to share what is seen.

Max-see Camera Used
Compact handheld camera/microscope that can connect to an electronic device.

Actual Images from Class…
All of the following images were taken of the Abacus plants from class week 6-8 of flower with the help of a student’s Max-see camera.
Thanks Aaron!

Pistil Trichomes
While there are some trichomes that have developed on the pistils these are not the ones to focus on.
Not all trichomes contain the desirable compounds
The Brown/Amber color of the pistil is an indication that this flower is nearing harvest time, but it is the inspection of the trichomes that makes the final decision on when to harvest.

Close, But Not Yet…
Here the stalked capitate trichomes can be seen.
However, most are clear indicating it is a little early to harvest.
There is some initial cloudy trichomes, but the overall population must be taken into consideration.

Previously Clear Now Cloudy
This indicates an increase the amount of cannabinoids the plant is producing.

Notice Some Purple to the Stalks
This is based mainly on the genetics and not environmental factors, it is possible for the grower to enhance the color based on various plant stressors.
Temperature
Light spectrum
Light Intensity
Purple Concentration
The purple pigment is a sign of Anthocyanin production.
This water-soluble pigment is in a larger class of compounds known as flavonoids.
While anecdotal, some people report better symptom relief with anthocyanins.

Peak Cloudiness
This would be the earliest recommended harvest, but typically the goal is to see a few ambers before harvesting.

First Ambers Can Be Seen
Typically this marks the “optimum time” to harvest.

Link to Lecture Slides: https://drive.google.com/file/d/1Igw7...

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