Life Cycle of a Cannabis Plant

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It’s easy to forget that cannabis is a plant, as medicinal and political factors veneer its simple growth. Like many plants, cannabis has evolved to cycle with the seasons. By understanding the cycle we can adjust a growing environment to match each phase.

Other Populace articles address the anatomy of a cannabis plant, the difference between growing from cutting versus seeds, and the difference between indica and sativa plants. This article takes a closer look at each phase of the life cycle of a cannabis plant.

From determining the sex of the plant to maintaining its overall health, each stage plays an essential role in developing the flower that is harvested, dried, and consumed. Every step involves unique requirements for light, nutrients, and care, that are needed to produce premium cannabis.

Cannabis is an annual plant that flowers during late summer and into the fall. Cultivators over the years have found ways to manipulate conditions indoors to mimic its natural growth cycle year round. Planting seeds to harvesting fully developed flowers can take anywhere from two to seven months, due to varying inputs. Regardless of timeline, cannabis goes through a five-phase process including germination, seedling, vegetative, flowering, and harvesting.

Germination Phase

24 Hours to One Week

The life of a cannabis plant starts with a seed. Seeds are usually light to dark brown colour and should feel dry and hard when squeezed -- if there is any give or a light green tint, the seed will be harder to germinate. Germination can take anywhere from 24 hours to a week.

On a basic level, germination involves the application of heat, air, and water to activate the seed from its dormant state and turn it into a seedling. The aim here is to provide optimal conditions for the seed to pop its taproot that will eventually make up the entire root structure that connects to the stalk of the plant.
Plant-Life-Cycle-Popped-Seeds

Seedling Phase

Two to Three Weeks

During the seedling stage, the taproot will extend down into the growth medium and branch outwards in search of water and nutrients. The stalk is delicate at this phase as it stretches towards its light source. The first set of leaves are embryonic leaves; these will only appear once in a plants life. They spread open to start absorbing light, kicking off photosynthesis and providing a place for the first fan leaves to grow. These first leaves are single fanned, at each node the number of fans per leaf increase until they represent the iconic symbol for cannabis.

Cannabis cells are totipotent, which means they can grow another plant from any part of the source plant. This is what makes the seedling phase different when growing from cuttings. With this method, the seedling will come from a fully developed mother that is genetically identical. This process requires rooting a clipped branch in a pre-moistened starter cube, allowing the roots to grow down from a formed seedling vs. the two growing in both directions simultaneously.
Plant-Life-Cycle-Drip-Line Drip line feeding system used at SunLab¹

there has been a cultural shift towards using natural, full-spectrum sunlight

It’s vital to keep the seedling happy and healthy with just enough water to thrive but not so much that it suffocates the developing root structure with oversaturation. Maintaining a clean environment and monitoring water intake are two ways to ensure that the seedling survives this stage and begins to form dense green foliage around its short stem. While a seedling, the plant needs between 18-24 hours of light a day to keep it healthy and give it the energy to grow.

Light sources have evolved with technology and cannabis specific lighting systems are now available. With cannabis normalization, there has been a cultural shift towards using natural, full-spectrum sunlight as the primary source as it provides light from all wavelengths on the spectrum, where artificial light is limited.

Vegetative Phase

Four to 12 Weeks

During the vegetative phase, growers focus on plant structure that can produce big flowers. Similar to how a factory is built to produce other goods, the veg phase is construction of a cannabis factory. There is serious growth during this stage as the stalk thickens and its roots spread throughout the growth medium grounding it in anticipation of thick, heavy flowers that form the main cola. It's crucial to make sure the plant is in a big enough container, and has enough hydration and nutrients for the best results.

Now is also the time you’re inner botanist can get to work observing the physical differences between indica and sativa characteristics. Short, bushy plants with broad fan leaves are consistent with indica strains; while taller plants with more spaced out nodes and narrower fan leaves will likely be sativa dominant. Keep in mind these two classifications are strictly physical and have little bearing on the psychoactive effect the flowers will produce.

The nodes are also vital towards the end of this stage as they will start to display signs of which gender the plant is. Male plants develop small sacs of pollen whereas female plants grow white hair-like pistils. Unless breeding cannabis, it's important to separate the male and female plants to avoid pollination. If pollinated, the female plant will use the majority of its energy to produce seeds instead of resinous flowers full of cannabinoids. During this phase, the vegetative plants continue to require 18-24 hours of full spectrum light a day for optimum growing conditions.

Flowering Phase

Six to Eight Weeks

Once pistils become more prominent at each node, growers initiate the flowering phase by reducing the light source to twelve hours a day. During the dark period, it's best to ensure the grow space is void of any light. Light leaks will stress the plant, and it could revert to a vegetative state. It’s a delicate time for the plant; reducing nitrogen and increasing phosphorus can help with bud development. If everything is going well, support will be needed as the weight of the growing flowers can cause branches to snap. Towards the end of this phase, growers focus on trichome development vs. the overall plant growth.
Plant-Life-Cycle-Backout-ShadesBlackout shades used for light management at SunLab¹

From the plants perspective, she is sadly becoming sexually frustrated without pollination. In an attempt to produce seeds, a frosty, sticky resin meant to trap the pollen from male plants appears. When observed with a microscope or jeweller loupe, this white frost is a forest of clear trichomes working overtime to produce THCA, the cannabinoid that once decarboxylated, provides the psychoactive effects associated with cannabis consumption. With no male plants around she will continue this process until it's time to harvest.

Late stage flowering is a sensitive time as well, as the trichomes will reach a THCA production peak and then ultimately that cannabinoid will begin to degrade to CBN. The result of this degradation is reportedly a less heady, energetic high and a more stoned, sleepy experience. Visually this looks like the clear or milky trichomes show amber hues similar to honey. Choosing when to harvest is determined by what kind of psychoactive effect the grower is looking to produce.

When to Harvest

The trichomes are the best reference to make an educated harvest decision, but the plant will give other physical cues as well. As the leaves start to yellow, the remaining nutrients stored within those fan leaves redistributes to the flowers. The flowers ripen, becoming more dense and aromatic, with prominent terpene profiles giving cannabis its distinctive scent. Once confident the trichomes have developed to provide the desired effect, it’s time to harvest the cannabis before drying and curing the yield to keep it fresh until it is ready to be consumed.