The Anatomy and Growth Cycle of the Cannabis Plant

A quick guide to the stages of a cannabis plant's growth.

lifecycle of the cannabis plant iStock / rclassenlayouts

Cannabis plants are annuals that flower magnificently for several weeks and complete their life cycle after one growing season. In this article, we’ll take a deeper look at the anatomy and life cycle of the cannabis plant.

Anatomy of the Cannabis Plant

Seeds:

The life of a cannabis plant begins in the seed. The cannabis seed is comprised of:

Hard outer shell: Mature seeds are tan or beige in color and are covered in unique, streaky dark markings called “tiger stripes.” Seeds have a round bottom and a pointed tip, with a seam along the exterior where the two halves will split when germinated.

Radical: the name for a root that is still inside the seed. 

Cotyledons: Cannabis is a “dicot” plant, meaning the seed contains two cotyledons, or rounded leaves that contain the seed’s nutrient reserves. 

Apical Tip: The point from which the rest of the cannabis plant will grow. It is situated between the cotyledons.

Roots

The root system anchors the plant to the soil medium, absorbs water and nutrients, and stores sugar and starches. Healthy roots of the cannabis plant require the proper amounts of moisture and air and should appear thick and bright white with loads of tiny hairs.

The tap root is the main root that extends downwards from the stem. Fibrous lateral roots branch off from the tap root. Outdoors, the root system can grow to roughly the same dimensions as the aerial plant. Tiny root hairs grow from the tap and lateral roots, absorbing the water and nutrients needed to nourish the plant.

The part of the cannabis plant where the root and stem meet is called the root crown, or neck. This occurs near the top of the soil where maximum root aeration occurs. Major cell division takes place at the root crown as it serves as the dividing line between upward (stem) and downward(root) growth.

Stem

The main stem is the primary vascular highway of the cannabis plant. It supports the plant’s weight and vertical growth. The stem carries water and minerals from the roots via xylem cells and transports sugars and starches via phloem cells. The process of photosynthesis produces these carbohydrates that are stored and used by the plant as energy.

Branches and Leaves

Branches emerge in pairs from leaf nodes on either side of the stem. The space between nodes is known as the internode. Indica-dominant plants tend to have shorter internode spacing than sativa-dominant plants.

Nodes are where pre-flowers appear and where growers can detect the first signs of sexual differences between plants grown from unfeminized seeds. When cutting clones, growers always include at least one node to plant beneath the substrate. The nodes produce rooting hormones called auxins which trigger the clone’s root development.

The first true leaves to emerge are a pair of single leaflets with serrated edges. Subsequent leaves are “palmately compound,” and increase from 3 to 13 serrated leaflets that emerge from the leaf stem at the point called the rachis. The shape of cannabis leaves varies from wide and flat to long and narrow. Fan leaves absorb sunlight to convert it into energy through the process of photosynthesis. Pores on the underside of the leaves absorb CO2 and release water and oxygen.

Flowers

Cannabis plants are dioecious, meaning the male and female sex organs are on separate plants. Male plants produce pollen that fertilizes female plants if allowed to reach maturity. Immature male flowers are called nanners because they look like green bananas. Unless they are being used to crossbreed strains, male plants are usually removed from the crop to prevent them from fertilizing the females.

Female flowers are grouped in tight teardrop-shaped clusters called colas. Pistils, the female’s primary sex organs, are composed of and ovule and protruding hairs called stigmas. In the wild, the pistils serve to catch pollen from male plants. Once a female bud becomes fertilized she will direct most of her energy to seed production. 

The unpollinated female plant will use her energy to grow trichomes, which secrete the sticky resin that contains cannabinoids. Sugar leaves protrude from and grow around the colas and may be trimmed at harvest or smoked along with the rest of the bud.

Growth Cycle of the Cannabis Plant

Germination

Seeds can lie dormant for a year or longer if kept in a dark, dry place. When exposed to light and moisture, the contents of the seed with expand and break through the outer shell. There are many ways to germinate cannabis seeds, but an easy method is to soak them in a glass of water for 24 to 72 hours. Plant the germinated seeds ½ inch deep in soil when a root tip appears and reaches three to five millimeters in length.

Seedling

Once planted, the sprouted plants begin to establish a root system and enter the seedling stage. The two embryonic leaves will emerge, followed by the first pair of single leaflets. This phase usually lasts 2-3 weeks and ends when the plant begins to produce five or more leaflets per leaf.

Vegetative

Plants become much more robust in the vegetative phase. This is a major growth phase for the plant. Some growers report that a healthy cannabis plant can grow up to two inches in 24 hours during this part of the growth cycle. Indoor growers typically maintain plants in the vegetative stage by providing 18+ hours of sunlight for 1-2 months.

Pre-flowering

In the pre-flowering stage you will begin to see the first signs of sexual differences between male and female plants. In male plants, the banana-like pollen sacs will begin to appear at the leaf nodes. Male and hermaphrodite plants must be removed immediately to prevent them from fertilizing female plants.

Flowering

Indoor growers transition their plants into the flowering stage by decreasing the light cycle to 12 hours per day. They will stop adding nitrogen to the soil but maintain or increase potassium and phosphorus. The plants will develop robust flowers with frosty while trichomes and sticky, pungent resin. Some of the pistils will begin to turn orange, amber, or brown. 

Harvesting

The time of harvest is crucial for the potency of your cannabis. There are several methods to determine when to harvest your cannabis, but a good rule of thumb is to harvest when over 50% of the pistils have darkened in color and 50-70% of the trichomes have turned milky white.

The Anatomy and Growth Cycle of the Cannabis Plant was last modified: by