The European Medicines Agency published Revision 1 of its GACP guideline on 9 July 2025, and it now includes a dedicated annex for indoor cultivation. That annex asks producers to keep daily records of critical process parameters and to set acceptance criteria for every batch. Harvest is where those records get tested hardest.
Cannabis harvest timing is the decision of when to cut a flowering crop, and it sets the cannabinoid concentration, terpene profile and batch uniformity you'll see on the certificate of analysis. For B2B importers, the right harvest is the one a supplier can document: days in flower, the decision criteria used, and how each part of the canopy was handled. A cut date on its own proves very little.
If you buy for the German, Australian or Israeli medical channel, your Qualified Person or quality team will eventually ask about harvest practice. It's cheaper to ask before the first purchase order than after a lot fails.
How cannabis harvest timing changes potency and terpenes
Cannabinoids don't accumulate in a straight line. Acid forms such as THCA and CBDA build through flowering, level off, and in some genotypes start to decline if the crop stays in the room too long. The commercial question is where on that curve your supplier cuts, and whether they cut at the same point every cycle.
What the research shows on harvest windows
A 2022 study in the journal Plants by Crispim Massuela and colleagues at the University of Hohenheim followed an indoor, CBD-dominant medical genotype. Plants were harvested at points between 5 and 11 weeks of flowering. Flower dry weight kept rising across that window, yet total CBD concentration did not change significantly. The highest total CBD yield per plant came at 9 weeks.
That finding should make buyers careful. A grower chasing weight can leave a crop in flower longer without the potency percentage moving much, so the COA number alone won't tell you whether the harvest was well timed. The study used a CBD-dominant plant, and the exact week won't transfer to THC-dominant export cultivars. The pattern does.
Terpenes shift late in flower
Terpenes are less forgiving. A 2020 study by André and colleagues on eight fibre-type cultivars grown in Switzerland found terpene content increased with maturation. The balance also moved from mostly sesquiterpenes early in flower to mostly monoterpenes by the end. Monoterpenes such as myrcene and limonene are also the most volatile fraction, so harvest timing and drying and curing standards shape the final terpene profile together. A supplier who gets one right and the other wrong still ships a flat batch.
Canopy position: one plant, several harvests
The Hohenheim team also tested flower by height on the plant. Top inflorescences measured 9.9% total CBD, against 8.2% in the middle and 7.7% at the bottom. That's a gap of roughly 22% between the top and the lower canopy of plants cut on the same day.
For an importer, this is the more useful result. A lot that blends top colas with lower-canopy flower can pass its potency specification and still show wide spread between sampled containers. Ask how lower-canopy material is handled before you ask which week the crop came down.
What GACP Revision 1 expects at harvest
The EMA guideline on Good Agricultural and Collection Practice (GACP) covers cultivation, harvest and primary processing of herbal starting materials. EU importers and their Qualified Persons look to it for the stage before EU-GMP takes over, and Revision 1 is far more specific about what an indoor producer has to show.
Section 11 sets the general rule: plants should be harvested when they reach suitable quality for the proposed use. Freshly harvested material must then reach processing as quickly as possible to prevent degradation and microbial growth. Annex 1 then adds indoor duties. Producers should identify critical quality attributes and critical process parameters, and set acceptance criteria for cultivation conditions in each batch. They must also keep daily digital records and standardise the process so results are reproducible.
| GACP Rev. 1 expectation | What it means at harvest | Evidence to request |
|---|---|---|
| Harvest at suitable quality (Section 11) | A defined harvest standard for each cultivar | Harvest SOP with written decision criteria |
| Prompt delivery to processing (Section 11) | Short hold time between cut and drying | Cut and dry-room entry times for the batch |
| Daily records of process parameters (Annex 1) | Light, climate and humidity logged through flower | Environmental log extract for the batch |
| Batch acceptance criteria (Annex 1) | Pass or fail limits for cultivation conditions | Batch record showing criteria were met |
| Standardised process (Annex 1) | The same flowering length every cycle | Days-in-flower history across recent harvests |
Canada works differently. The Cannabis Regulations set Good Production Practices covering premises, sanitation, standard operating procedures and testing, but they don't define when a crop should be cut. Health Canada inspects against those practices, not against a harvest window. For a wider view of cultivation-stage controls, see our GACP certification checklist for B2B buyers. A Canadian licence proves the domestic baseline. Your EU Qualified Person will want the batch record.
The 5-point harvest timing check for importers
Most Canadian LPs can tell you their harvest date. Fewer can tell you why they cut on that day. The gap between those two answers is where batch variance starts, and it's the part of supplier qualification buyers skip most often.
- Days in flower for each batch. Ask for the flip date and cut date across the last six harvests of the cultivar you're buying. A spread of a week or more with no written reason points to a schedule-driven harvest, not a quality-driven one.
- The written harvest standard. Trichome inspection under magnification is common practice, but on its own it's a judgment call. A credible SOP defines what the grower looks for, who signs off, and whether pre-harvest potency testing backs up the visual check.
- Canopy fraction handling. Ask whether lower-canopy flower is graded separately, sold as a different lot, or blended in. A sampling plan for batch testing only gives you a representative result if the lot was uniform to begin with.
- Cut-to-dry hold time. GACP Section 11 asks for prompt delivery to processing, so request the time stamps for cut and dry-room entry on your batch.
- Cross-harvest COA history. Compare potency and terpene results across at least three harvests, all from ISO/IEC 17025 accredited testing, against the potency tolerances B2B buyers set in your supply agreement.
A supplier who can't produce days-in-flower data for your cultivar isn't ready for the EU medical channel. Consistent numbers across harvests are the only real proof that a harvest standard exists outside the SOP binder.
Where harvest timing goes wrong in export batches
Cutting to the room schedule instead of the cultivar
Room turnover pushes growers to cut on a fixed cycle so the next crop can go in. That works for a cultivar whose window matches the schedule. For a slower-finishing cultivar, it means an early harvest every cycle and a terpene profile that never matches the reference batch you approved. Our guide to cannabis cultivar consistency covers how to hold suppliers to that reference.
Letting the crop run late for weight
The Hohenheim data show why this is tempting, since dry weight kept climbing while concentration held flat. Extra weeks add kilos, but they can also raise CBN, a degradation product of THC, and cost you volatile terpenes. Those kilos rarely cover the cost of one rejected lot.
A slow hand-off from cut to dry room
Wet flower left too long in bins is exposed to heat build-up and microbial growth, which are exactly the risks GACP Section 11 names. The guideline also warns against overfilling and stacking containers. The fix is operational: smaller harvest blocks, staged cuts, and drying capacity sized to the harvest rather than the other way round.
AlphaLeaf is a Health Canada Licensed Producer with an indoor cultivation facility in Montreal, where refined genetics are grown in controlled rooms and every lot is hand-trimmed. Our batches carry ISO-certified testing and full traceability from harvest to shipment, and we hold export authorisation under the Cannabis Act to supply EU import partners and the German medical channel.
Want to check harvest records for a specific cultivar? Contact our team and ask for the batch file. Then compare it with your current supplier's.
Frequently Asked Questions
When is cannabis ready to harvest for medical export?
There is no single week that suits every cultivar. Readiness should follow a written harvest standard for each cultivar, using trichome inspection and ideally pre-harvest potency testing. Flowering length should also stay consistent from cycle to cycle so batches remain comparable.
Does harvesting cannabis later increase THC?
Not reliably. Research on an indoor medical genotype found flower weight kept rising late in flower while cannabinoid concentration stayed largely flat. Leaving a crop too long can also raise CBN, a THC degradation product, and reduce volatile terpenes.
Does EU GACP set a harvest date for cannabis?
No. The EMA GACP guideline says plants should be harvested at suitable quality for the proposed use. Revision 1 asks indoor producers to define critical process parameters, set batch acceptance criteria and keep daily records, which is how harvest decisions get documented.
Why do top colas test higher than lower buds?
Flower at the top of the canopy usually gets the most light, and research has found it carries more cannabinoids. A 2022 University of Hohenheim study measured 9.9% total CBD in top inflorescences against 7.7% at the bottom of the same plants, a gap of about 22%.
What harvest records should a B2B cannabis buyer request?
Ask for flip and cut dates across recent harvests, the written harvest SOP, and how lower-canopy flower is handled. You should also request time stamps from cut to dry-room entry and COA results from ISO/IEC 17025 accredited testing across at least three harvests.
