When Is The Right Time To Harvest?
- John Moritz
- Apr 6
- 6 min read
As a novice indoor grower just starting, I had many questions and concerns, with one being the most prominent: When is the right time to harvest? This question often comes up in cannabis groups and forums. Let's explore the stages of the plant's growth and the best time to harvest cannabis.
The Vegetative Stage
The cannabis plant goes through an initial vegetative growth phase, during which it receives more hours of light than darkness. Growers typically choose a light cycle of eighteen hours of light and six hours of darkness, commonly referred to as an 18/6 light schedule. As long as this light cycle, or a similar one, is maintained, the plant will continue to vegetate and not begin to flower.
To trigger the transition from the vegetative stage to the flowering stage, the light cycle must be reduced to twelve hours of light and twelve hours of darkness, known as a 12/12 light cycle.
For those growing autoflowering plants, changes in the light cycle do not affect the plant's growth. Autoflowers will usually begin to flower within the first 3-4 weeks of growth.
The Flowering Stage: The First Few Weeks
The flowering stage is an exciting time for most growers, as it marks the beginning of flower production—what every grower is ultimately after.
Cannabis is a dioecious plant, having distinct male and female plants. In nature, this trait is relatively rare, as only about six percent of flowering plants are dioecious. If you are growing from regular seeds, you'll need to determine the sex of your plants as soon as they show the first signs of flowering. Female plants will begin to produce bracts and stigmas, while male plants will form pollen sacs. It's important to remove male plants from your grow space immediately to prevent pollination. If you are growing from feminized seeds, whether photoperiod or autoflower, you shouldn't need to worry about sexing the plants, as the likelihood of encountering a male plant is extremely low (over 99%).
You should closely monitor your plants to ensure they do not exhibit any hermaphroditic traits, as these can lead to your female plants producing male pollen sacs. If pollen is released into the air in your grow space, it can cause your female plants to produce seeds, which is undesirable unless you're planning to breed more plants. This is equally applicable to those growing from regular seeds. It’s advisable to carefully observe all your female plants until at least the start of the fourth week of flowering. Hermaphrodites typically appear during the second or third week of flowering, making it crucial to keep a vigilant eye on the plants for any potential pollen sacs that may develop. Pay special attention to the lower parts of the plant and beneath the flowers. Though hermaphrodites are rare under optimal growing conditions, it's important to consistently observe your plants at least twice daily during these critical early weeks and to remove any hermaphroditic plants if they appear. Allowing your female plants to be pollinated by males or hermaphrodites can result in an earlier harvest and significantly lower potency. Once a plant is pollinated and begins producing seeds, it will divert energy away from trichome production. This is why sensimilla, or seedless cannabis, is generally much more desirable than seed-bearing cannabis.
If you let your plants vegetate for an extended period, say six weeks or more, you may be able to determine their sex before flowering by observing preflowers. These preflowers often develop before the light cycle is changed to 12/12 to induce flowering. Preflowers can be a reliable indicator of a plant's sex prior to flowering.
During the first few weeks of the flowering stage, you will notice that the plants stretch and grow rapidly, a phase often referred to as the "stretch" phase. It is not uncommon for plants to double in height during the first three to four weeks of flowering. Be sure not to allow your plants to vegetate for too long without adequate space, especially concerning ceiling height. It’s best to plan ahead and ensure sufficient space for your flowers to develop fully while maintaining a safe distance between the flowering tops and your grow lights. If space is not an issue, you can vegetate your plants for as long as you'd like before changing the light cycle to induce flowering. Low-stress training techniques can also help manage how much the plant stretches towards the light, encouraging it to grow more outward than upward.
The Flowering Stage: Weeks Four Through Five
As you reach weeks four to five of the flowering stage, you will likely want to defoliate your plants. Removing large leaves allows the plant to redirect its energy toward producing flowers and trichomes, rather than focusing on leaf growth. This process also improves airflow around the plant, reducing the risk of issues such as powdery mildew, botrytis, or pest infestations. At this stage, trichome development and overall flower growth begin to accelerate. Your buds are still developing and are not yet ready for harvest.
The Flowering Stage: The Final Weeks
Most indoor plants typically take eight to ten weeks to reach maturity during the flowering stage. However, this duration can vary depending on the specific cultivar. Plants that have a stronger sativa influence may require more time to finish flowering, often taking eleven weeks or more. In contrast, those with genetics that lean heavily towards indica can often mature in less than eight weeks of flowering.
As the flowers mature, you'll observe several changes occurring. During the final weeks, the flowers may swell, sometimes doubling in size within just a few weeks. You'll also notice the stigmas changing color, transitioning from white to yellow, orange, red, brown, or even purple. When most of the stigmas begin to change color, it's a good indicator to start examining the buds closely daily for any changes in trichome development, especially their color.
It's All About the Trichomes
Trichomes are the best indicator of whether your flowers are fully mature and ready for harvest or need more time to mature. These tiny, translucent structures have globule-shaped heads that swell larger as the plant matures. Trichomes give buds their 'frosty' appearance, with some cultivars producing more trichomes than others.
Initially, the trichome heads are translucent in color. As the plant progresses through the flowering stage, these heads develop a milky white coloration, eventually turning amber as the plant nears full maturity. Most growers prefer to harvest their plants when the trichome heads are about 10% amber with the rest being milky. Some growers prefer a higher concentration of amber trichomes, for a more 'couch lock' effect. More amber trichomes indicate higher levels of CBN, which results in a more sedative effect from the flower. Conversely, if you harvest with fewer amber trichomes and more milky ones, the effects of the flower will be slightly more uplifting and energetic.
When examining trichome heads, focus on the buds rather than the leaves. This is because the trichomes on the leaves tend to mature much faster than those on the buds.
They're So Small. How Can I Possibly See Them?
Trichomes are small, even when fully mature, measuring between 50 and 100 microns (0.002 to 0.004 inches) in diameter. Examining the trichomes closely is essential for determining the best time to harvest, so you'll need good magnification for a detailed view. There are several options available, some of which are better than others.
To examine trichomes, you will need more than just a magnifying glass. A magnification of at least 50x is the minimum requirement, but 100x or higher provides the best opportunity to examine the trichomes. There are various jeweler’s loupes and magnifiers on the market that can achieve this level of magnification. A microscope is also a good option for closely examining trichomes, although it may require removing a small sample from the plant. Digital microscopes are affordable, with many models costing $150 or less. These can provide clear images for closer inspection on a digital monitor.
The good news is that you might not need any of the aforementioned tools at all. Most people have smartphones, and today's phone cameras are capable of producing sharp, high-resolution images with ease. I like to photograph the buds by pinching a sugar leaf between my middle and ring fingers on the same hand that's holding my phone. This allows me to stabilize the phone and the bud, resulting in better photos with minimal blurring. Adjust the distance between the camera lens and the flower until it is in focus, then take your best shot.
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