Trichomes are small appendages that look like hairs, they are produced by marijuana and other plants. They are too small to be seen properly by the unaided human eye and require inexpensive observation tools.
With female marijuana plants, capitate trichomes are resin glands with round heads that form on top of them.
They are a rich source of THC, other cannabinoids, as well as terpenes. Monitoring capitate trichomes will help you to best judge when the plants are ready for harvesting.
The trichomes can be found in their largest concentration on the buds of flowering female marijuana plants.
All marijuana strains produce trichomes that start out clear (image 1) some have a slight yellow tinge.
As they age, most strains will then turn a milky translucent color (image 2).
Towards the end of flowering they will turn light brown (image 3) or in rare cases a reddish color.
Light brown or reddish trichomes are an indication that THC is breaking down into CBN. As the proportion of CBN goes up the resulting marijuana becomes less potent.
With mainly or pure indica strains for maximum THC content, and strongest high or most potent medicine possible, try harvesting your plants after about 50%-75% of the round heads on top of the trichomes have turned from clear to a milky translucent color.
Don't overreact and think that you have to harvest or the crop will be ruined because you see brown trichomes.
You should harvest after at least 50%-75% of the round heads have turned milky and before more than 20%-30% of the trichomes have turned light brown.
Many experienced growers working with mainly or pure sativa strains will wait until most of the larger buds have trichomes that have about 20%-30% brown trichomes.
If you wait too long and harvest when the THC in a majority of the trichome has degraded into CBN, the THC content and potency of the marijuana will suffer. The high, as well as some of the medical properties, will be diminished.
The amount of time required for a plant to mature will vary with the marijuana strain being cultivated as well as the growing conditions it experiences.
Image 4 was taken on the harvest day of a crop. Almost 100% of the trichome heads on this, and other buds on the same plant, had turned milky translucent or light brown. See more trichome images and info about the harvest here.
Remember to judge the color of the round head of the resin gland and not the stem. Even though the trichome stem is still clear on most of the trichomes in image 4, the round heads that top the trichome have almost all turned milky translucent white.
1 --- In image 1 you can see the milky translucent color starting to fill the clear round head on top of the trichome.
2 --- In most cases, not all buds on the same plant mature at the same time. You can harvest a crop all at once or you can harvest each branch or bud when it is ready.
If you harvest a crop all at once, monitor the largest buds on each plant and harvest the crop when a majority of those large premium buds are ready.