Stage 04: Medicinal Cannabis Harvesting Stage

Medicinal Cannabis Harvesting Stage

Medicinal Cannabis Harvesting Stage

This page covers information about the 4th stage of the medicinal cannabis harvesting production process, the harvesting stage. Harvesting is when the flowers are removed from the plant and the rest of the plant is discarded following GMP waste management processes.

When to harvest medicinal cannabis

Harvesting cannabis flowers at exactly the right time is critical for optimizing the active ingredient content of the flower. Harvest too soon and you lose potency and yield. Harvest too late, and you can end up with high levels of CBN.

  • Some cannabis growers use a nutrient flushing process to stress the plants, forcing them to flower and boost THC levels.
  • Like most plants, a cannabis plant will put all its energy into flowering and reproduction if it feels threatened.

Medicinal Cannabis Harvesting Stage: Choosing the right time to harvest

The right medical cannabis harvesting stage depends on the cannabis variety you are growing and the active ingredient you are seeking. Timing can vary from a few days to a few weeks between different cannabis varieties. With most varieties, the window for optimum harvest is narrow – a few days at best.

Like any horticultural product, knowing the visual and physical signs to look for to determine harvest time relies on knowledge and experience. Typically, a grower will use a magnifying device, like a Jeweller’s Loupe or a digital microscope to examine the resin-filled trichomes on the flowers.

Trichomes: Definition and Images

Trichomes are tiny hairs, each attached to a resin-filled droplet (refer to image). Their appearance changes as the flower ages.  For large scale operations, more sophisticated testing in a purpose-built laboratory would be appropriate, with equipment to test all of the TGO 93 requirements.

Number of medicinal cannabis prescriptions in Australia - how many prescribers
Abstract macro detail of cannabis bud (green crack marijuana strain) with visible hairs and trichomes

The harvesting process

Once the optimum harvest time has been determined, work crews can move in. They will cut off the top 30 cm of each flowering stem. These cuttings are placed into tubs to be taken to the drying room. In a large facility, harvest represents considerable manual handling and associated costs.

It’s not hard to see the playoff between selecting a day to begin harvest, when the active ingredients in the plant are at their peak, versus having expensive labour on standby to begin the harvest. Growing the plants indoors gives the maximum control over the harvesting process, whereas broadacre cultivation is at the mercy of the weather and other external factors.

All parts of the plant contain active ingredients, just at lower concentrations than the flowers. For this reason, the remaining plant material must be responsibly disposed of. This means either hot composting on-site or using a specialist waste disposal company, licenced for such work. The disposal or recycling of pots and grow media must also be considered.


The propagation of cannabis plants is regulated by the Australian Office of Drug Control. You must hold a licence from them to cultivate cannabis (they control the plant during its lifecycle). Once the plant has been harvested and moves into the production of the final medicinal product then the Australian Therapeutic Goods Administration (TGA) is the regulator. This part of the manufacturing process must comply with the current Good Manufacturing Practice guidelines. These rules are designed to ensure the safety and efficacy of all pharmaceutical drugs sold in Australia. The rules cover everything from facility design through production processes to the packaging, labelling, storage and transport of the final drug product.

Facility design

When designing the flower house of a medicinal cannabis facility, it’s important to consider the following to ensure a smooth harvest:

  • Manual handling during the harvest – can automation be used to reduce labour costs and potential for injuries?
  • Will the ability to ‘flush’ the plants be required? Should this be automated?
  • What testing facilities are needed onsite to identify the optimum time to harvest?
  • How will the waste plants and materials move through the facility? How will they be disposed of or recycled?

Services PharmOut offers:

PharmOut’s Australian and US-based Architects, Engineers, Scientists and Growers can design a complete turn-key solution, or you may need help with only specific areas, such as:

  • Refining the process of harvest time identification
  • Material flows through the flower house
  • Laboratory testing facilities

Disposal/recycling of waste materials

PharmOut’s cannabis consulting experts can also help in the following areas with access to our international expert Cannabis Growers, Facility Designers, Engineers and Architects.

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