Europe's CBD industry has spent a decade moving south. Longer season, more sun, cheaper land. The logic looks obvious until you read what actually happens inside the plant, and what else comes bundled with growing down there. Sunlight drives cannabinoid production. But sunlight and heat are not the same thing, and Scandinavia has the one without the other.
The industry's map
Look at where Europe's CBD hemp is grown. Italy, Spain, Portugal, the Balkans. Ask why, and the answer comes without hesitation: longer season, more sun, lower cost.
The last two hold. The first, more sun, is more complicated than the industry believes. And nobody has costed what comes with it.
Scandinavia, meanwhile, has been written off. Season too short, too cold, too far north. The argument has never been tested against data, because nobody bothered to collect any.
Sunlight governs, but sunlight is not heat
That light drives cannabinoid production is established. In hemp inflorescences, total CBD rose 36.88% when light intensity was increased, and the researchers could follow the mechanism down to gene expression: the entire biosynthetic pathway from hexanoate to cannabinoids was coordinately upregulated, with a significant increase in CBDAS, the enzyme that builds cannabidiolic acid (Frontiers in Plant Science, 2025).
Genetics determine which cannabinoid the plant makes. That is settled at a single locus with Mendelian inheritance (de Meijer et al., Genetics 2003). But how much is not fixed in the seed, it is settled in the field, and light is the strongest lever.
This is where the industry goes wrong. It read "more sun" as "further south", and treated the heat as a free bonus.
It is not free.
The ceiling nobody costed
Holweg et al. (2025) compared four cultivation cycles in climate chambers, two at 25/21 °C and two at 31/27 °C, across three light levels (600, 900 and 1,200 µmol·m⁻²·s⁻¹). For CBD-rich genotypes, total cannabinoid yield fell from over 200 g/m² to under 100 g/m². The effect on biomass was genotype-specific: inflorescence dry matter fell in the CBD-rich cultivar but was unaffected in the THC-rich one. Published in Environmental and Experimental Botany 230, 106085 (doi:10.1016/j.envexpbot.2025.106085).
More than a halving. Across six degrees.
The lower flank is mapped too: total CBD rises across the range 0.5–22 °C, at roughly 0.09 percentage points per degree (J. Cannabis Res. 2025). The authors, however, attribute the increase mainly to plant maturity rather than to temperature as such. So this is not a claim that cooler is better, but about where the ceiling lies: in Holweg's trial, 25/21 °C gave more than twice the cannabinoid yield of 31/27 °C. Where a lower limit lies is not established in the studies cited here.
Visby in July: the monthly mean sits just above 17 °C (SMHI).
Bologna in July: 31.5 °C mean maximum and 19.3 °C mean minimum, with peaks around 36.5 °C on the hottest days (Climates to Travel). Bologna sits on the plain's southern edge.
Visby sits below even Holweg's cooler treatment arm. Bologna's daytime temperature is level with the warmer arm, not as a heatwave, but as a normal year.
What the North actually has
Gotland is Sweden's sunniest region: Visby and Hoburg record just over 2,000 sunshine hours per year as a 1991–2020 normal. At midsummer, daylight runs close to 18 hours.
It is the combination that is unusual, not the individual parts. Long light days and a temperature that rarely reaches the ceiling. Southern Europe has the first but pays for it with the second.
Add what a sunshine-hours table does not show: calcareous, free-draining soil; sea wind that keeps the canopy dry and lowers fungal pressure; and a short, intense season in which the plant builds without pausing for heat stress.
No single one of those factors decides it. Together they do.
The bundle that comes with going south
This is usually where the discussion stops. It should not, because there is a third factor the industry never raises: where that south actually is.
The European Environment Agency names the Po Plain explicitly in its country assessment of Italy: emissions have fallen over two decades, "although some areas, such as the Po Valley, still face difficulties." The same assessment records that Italy's PM2.5-related mortality in 2022 was 12 percentage points above the EU average, and that the fall in PM2.5-attributable premature deaths between 2005 and 2022 reached 32% in Italy against 45% across the EU (EEA, Europe's environment 2025).
The cause is geographic, and therefore permanent. The Po Plain is bounded by the Alps to the north and the Apennines to the south, which produces stagnant air and limited air exchange: emissions stay in the basin rather than ventilating out (Frontiers in Environmental Science, 2023).
And here the evidence runs out. The comparison one actually wants, how heavily treated the crop is, country by country, cannot be made from EU statistics. Eurostat says so plainly: data on actual use and application rates "are not collected annually or comparable between the countries" (Eurostat). Sales volumes exist, but they track farmland area, France, Spain, Germany and Italy account for the largest volumes and also for 52% of the EU's utilised agricultural area.
To conclude from that that southern European hemp is more heavily sprayed would be to pretend to know something nobody knows. What does hold is the next section: for hemp, the growing site matters regardless of what the statistics can show.
Why this weighs more for hemp than for other crops
For most crops the surrounding environment is one quality factor among many. For hemp it is a product specification.
Hemp takes up heavy metals from the soil. A review in Remediation Journal 2026 (Ansari et al.) describes strong tolerance and uptake capacity for cadmium, lead and arsenic, mainly in the roots. The plant also takes up PFAS, but selectively, and overall PFAS removal from the soil is rated low to moderate. The same property that makes the plant useful for soil remediation makes a site's actual values decisive for the finished product.
What the market looks like today, read correctly: across 202 commercial CBD products, heavy metals were detected in 44 and pesticides in 30, but only around 3% exceeded regulatory thresholds. The genuinely striking finding was different: 74% deviated by more than ±10% from their own stated content, and residual solvents were present in 90% of products (Gidal et al., Frontiers in Pharmacology 2024).
The market is not primarily dangerous. It is imprecise. It does not know what it is selling, and it can rarely say where it grew.
The data point, and whose it is
The reader needs to know whose figure this is. The data point below is my own. The seed, the Gotland crop and the published note all come from Helsama OÜ, which I own, and the note is self-deposited on Zenodo, not peer-reviewed. The cannabinoid analysis was carried out by an outside laboratory using HPLC-UV; the selection, the sampling and the publication were not. Weigh the figure accordingly.
Identical hemp seed grown at two locations, analysed by the same method:
| Growing location | CBDA (% w/w) |
|---|---|
| Gotland, Sweden | 8.83 |
| Italy | 6.64 |
+33% for the northern-grown material. The note is published with a DOI under CC BY 4.0 (10.5281/zenodo.21250740), a DOI is a persistent address, not a mark of quality.
The comparison has an unusual methodological strength: the cultivar is day-neutral. Autoflowering hemp flowers on an internal clock rather than on daylength, the genetic basis is mapped to the Autoflower2 locus carrying the FT ortholog CsFT1 (Dowling et al., The Plant Journal 2024). The plant should therefore have had roughly the same life-cycle length at both sites. That is an inference from the cultivar's biology, not a measurement. Photoperiod, the classic confounder in every latitude comparison, is not adjusted away after the fact; it is engineered out by the plant's own biology.
What this is not
Underdog stories get worse when they are overstated, so:
- It is n=1 per site. A paired observation, not a controlled trial. The published note says so itself.
- The genetics are confirmed, the Italian growing location is not. That this is the same seed and the same cultivar is not in question; it is the whole premise of the comparison. What is missing is where in Italy the reference crop stood. The seed supplier will not disclose it, because it protects its customers. Italy spans ten degrees of latitude, so the Po Plain is used here as a representative southern European growing environment, not as the reference sample's site.
- The light mechanism has a ceiling. The study above measured 200→600 µmol·m⁻²·s⁻¹. A separate study found concentration unchanged between 600 and 1,000 (Llewellyn et al., Frontiers 2022). Full sun exceeds that level at both sites. Any northern light advantage must therefore act through the length of the day rather than its intensity, and that is not directly tested.
- Holweg was not read in the original. The figures are verified verbatim through a citing peer-reviewed article; the original sits behind a paywall.
- Cultivation data is missing. Radiation sums and canopy temperature are not being logged this year, so the mechanisms cannot be separated on present evidence.
The conclusion
The industry moved south to fetch sunlight, and brought back the heat with it. It optimised for season length and missed the ceiling.
Scandinavia is an underdog in this industry in a purely quantitative sense, a few hundred hectares against tens of thousands. But the underdog position rests on an assumption that does not survive checking: that further south means better.
Sunlight governs. It simply is not only down there.
What is missing now is not more argument. It is a multi-year field trial with identical day-neutral genetics across several European latitudes, with logged radiation and canopy temperature and a single analytical laboratory. It does not exist in the published literature. With day-neutral cultivars it is easier to run than it has ever been.
Someone should. Preferably someone with no product to sell.
Updated 7 October 2026.