Hemp is not simply cannabis grown for non-intoxicating purposes. It is a set of distinct crop types with fundamentally different agronomic requirements, processing infrastructure, and market chains.
Industrial hemp (Cannabis sativa L. with THC content below regulatory thresholds) spans three primary production types: fiber, grain (seed), and CBD/phytocannabinoid. Each type requires different cultivar genetics, planting density, harvest timing, and post-harvest processing. Conflating these types, or applying the agronomic practices of one to another, is a common error in hemp production planning.
Legal status box: Thailand (checked 14 October 2026)
- Hemp is defined by plant THC below 1.0% (dry weight) in leaves and flowering tops. Hemp extracts must be at or below 0.2% THC.
- Hemp flower is still a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis) B.E. 2568 (issued 26 June 2025), whatever its THC level. Flower may be dispensed only against a PT 33 prescription from an authorised practitioner (no more than 30 days per prescription, single use). Flower that is sold or exported must come from a GACP-certified cultivation site.
- Advertising or selling flower online is prohibited. Recreational use is not permitted.
- Two Ministerial Regulations B.E. 2569 tightened licensing (cannabis/hemp extracts, in force 26 April 2026; controlled-herb licences No. 2, in force 30 April 2026). They do not change the PT 33 rules.
- The Cannabis Control Act is still a draft. The Cabinet approved it on 22 September 2026 and sent it to the House. The 1.0% plant and 0.2% extract thresholds may change under it.
Related topics: hemp flower under the controlled-herb rules → bai251; THC thresholds → topic 203; hemp exports → bai216.
Regional note: Growing hemp, and especially CBD hemp, is illegal or tightly restricted in much of Southeast Asia, including Vietnam, Malaysia, Singapore and Indonesia. This article is agronomic education. It does not encourage anyone to grow hemp where it is not licensed.
1. Hemp Crop Types and Their Distinct Requirements
1.1 Fiber Hemp
Fiber hemp is grown for the long bast fibers in the stem’s outer layer and for the shorter hurds (shive) from the woody core. Uses include textiles, rope, composites, insulation and hempcrete.
- High planting density: 150–250 plants/m². Dense stands produce tall, slender, minimally branched stalks with the longest bast fiber.
- Variety type: Dioecious or monoecious fiber varieties with low resin, minimal branching and fast elongation.
- Harvest timing: Pre-flower or early flower for premium textile fiber; later harvests give lower-grade fiber and combined fiber/hurds.
- Water: Hemp develops a deep tap root and can reach subsoil moisture, but seedlings need steady moisture without waterlogging.
- Expected yield: 5–12 tonnes dry stalk per hectare (Struik et al., 2000; Amaducci et al., 2008).
Retting and fiber processing are capital-intensive and currently limited in Southeast Asia. → See article 81 (fibre retting and processing).
1.2 Grain/Seed Hemp
Hemp seed is grown for food and feed: cold-pressed oil rich in omega-3 and omega-6 fatty acids, and shelled seed (hemp hearts). Oil content is around 30%; Thailand’s Highland Research and Development Institute (HRDI) reports 28–29% oil and 21–23% protein for its RPF lines.
- Moderate planting density: 25–55 plants/m² to allow branching and multiple seed heads.
- Variety type: Early-finishing varieties. Dual-purpose fiber/seed varieties exist but usually compromise both.
- Harvest timing: When most seed is mature. Seed shatters before the whole head ripens, so timing is critical.
- Expected yield: 500–1,500 kg seed per hectare.
HRDI recommends RPF1 and RPF3 for seed production in Thailand.
1.3 CBD/Phytocannabinoid Hemp
CBD hemp is grown for cannabidiol and other phytocannabinoids from female flowers and leaves. It is the most discussed type among small-scale growers in Europe and North America. In Thailand its flower is a controlled herb (see the box above), and in most of the rest of Southeast Asia growing it is not legal.
- Low planting density: 1–3 plants/m² for maximum branching.
- Female-only planting: Feminized seed or clones. Pollination diverts the plant’s energy into seed instead of resin.
- Variety type: High-CBD, low-THC varieties with documented chemotype stability.
- Harvest timing: Set by cannabinoid testing as well as trichome maturity (Section 6).
- THC compliance: Test against the threshold that applies where the crop is grown: Thailand 1.0% for the plant, EU and United States 0.3%. The 0.2% figure is Thailand’s ceiling for extracts, not for plants.
2. Cultivar Selection and Certification
2.1 Why Certified Varieties Matter
In most jurisdictions where hemp is legal, only approved or certified varieties may be grown commercially. These varieties have shown THC at or below the legal limit under monitored conditions, and their CBD/THC ratio, growth habit and maturity timing are predictable. Saved or uncertified seed puts the regulatory risk on the grower.
The EU Common Catalogue of varieties of agricultural plant species lists several dozen approved hemp varieties. In Thailand, the certified fiber varieties are HRDI/Royal Project lines (Section 7).
2.2 Chemotype Classification
| Chemotype | Dominant cannabinoid | THC:CBD | Typical use |
|---|---|---|---|
| Type I | THC | THC-dominant (>1) | Drug-type cannabis |
| Type II | THC + CBD | Intermediate (~1) | Mixed |
| Type III | CBD | CBD-dominant (THC well below CBD) | Fiber and CBD hemp |
| Type IV | CBG | CBG-dominant | CBG market |
| Type V | None | Negligible cannabinoids | Experimental/fiber |
CBD hemp varieties are Type III. The chemotype is genetically fixed: a Type III plant does not become Type I under stress. What changes is the THC percentage. Total THC rises together with CBD as the flowers mature, peaks around 6–7 weeks after anthesis, and then declines at senescence (J. Agric. Food Chem., 2020). In NC State trials, two CBD cultivars reached 0.3% total THC 41–50 days after floral initiation (Suchoff et al., 2022). A non-compliant result at 0.3% is therefore usually a timing problem in a Type III plant, not a change of chemotype.
2.3 Autoflowering vs. Photoperiod Hemp Varieties
Photoperiod varieties flower when days shorten below a critical length. In temperate zones, flowering starts in mid-summer and harvest follows in autumn. In Thailand they flower naturally in the short-day season. HRDI reports that RPF1 and RPF3 flower each year in roughly October–February, so planting date determines plant size (Section 7).
Autoflowering varieties flower by age regardless of day length. In Thailand they are the realistic option for a dry-season crop, and only with irrigation.
On CBD and THC levels: advertised figures of “10–16% CBD with <0.3% THC” are unrealistic at normal ratios. At about 20–25:1, 16% CBD means roughly 0.6–0.8% total THC. In the NC State trials, 0.3% total THC was reached at about 8% total CBD (Suchoff et al., 2022). In the Midwest Cultivar Check Program, 28 of 49 CBD-dominant cultivars (57%) exceeded 0.3% at some point during flowering (UW–Madison, 2024). High-CBD lines usually exceed 0.3% total THC at full maturity.
3. Site, Soil and Nutrition
3.1 Soil and Drainage
Hemp tolerates modest fertility, but yield depends on:
- pH: about 6.0–7.5 for all crop types (University of Wisconsin Extension, cited by Rodale Institute). Below about pH 6, check for aluminium and manganese toxicity. At high pH, iron and zinc deficiency symptoms are often a pH problem rather than a lack of nutrients.
- Drainage: This is critical. HRDI names root and stem rot from wet or waterlogged soil as the main problem in Thai hemp, with the first 30 days the most vulnerable period. Choose well-drained loam or sandy loam and dig drainage furrows in the rainy season.
- Weeds: Dense fiber stands shade out weeds after canopy closure. Low-density CBD plantings need mechanical or mulch weed control in the first weeks.
3.2 Climate
Germination needs warm soil (>8°C), which is not a limitation in lowland Southeast Asia. Seedlings are frost-sensitive, which matters in temperate regions and at the highest Thai elevations. Prolonged high humidity at flowering raises botrytis risk in CBD hemp.
3.3 Nutrients by Crop Type
One consistent set of numbers. Adjust to a soil test.
| Crop type | Target pH | Total N | Source |
|---|---|---|---|
| Fiber | 6.0–7.5 | up to ~150 kg N/ha (optimum without a cover crop in Kutztown, PA trials) | Rodale Institute |
| Grain | 6.0–7.5 | ~100 kg N/ha (same trials) | Rodale Institute |
| CBD | 6.0–7.5 | No agreed optimum. General hemp guidance is 50–100 lb/ac (≈56–112 kg N/ha), split, with 20–25% at planting | Univ. of Delaware Extension |
- N during flowering (CBD): The evidence is mixed. A controlled-environment study found the highest cannabinoid concentrations at low N, while a high-desert field trial found that cannabinoid concentration depended on cultivar and harvest timing, not N rate. A practical approach is to supply most N during vegetative growth and avoid heavy late applications.
- Legumes: In the Kutztown trials, hairy vetch and winter pea cover crops supplied enough N for hemp without extra fertilizer.
- P, K, S: Apply according to the soil test. Highly leached tropical soils may also need sulfate-containing fertilizer.
4. Crop Rotation and Soil Health
Hemp works best as a rotation crop:
- Weed suppression: A dense fiber canopy reduces weed pressure for the next crop.
- Disease break, with limits: Hemp is not a host of clubroot (Plasmodiophora brassicae), but it is susceptible to Sclerotinia sclerotiorum, which also attacks sunflower, soybean and canola. It gives no disease break in rotations that already contain these crops.
- Heavy metals: Hemp takes up heavy metals mainly when grown on contaminated land. The phytoremediation work involved heavily contaminated soils (Linger et al., 2002; Rheay et al., 2021). Crops from such sites are unsuitable for food or extraction.
- Seed hulls: Incorporated hulls add little nitrogen. At 3% protein they contain about 0.48% N, roughly 5 kg N per tonne of hulls.
Temperate rotations (cereal → hemp → cereal or oilseed) are well documented in Europe (Struik et al., 2000).
In Thailand, photoperiod hemp occupies the rainy-season upland slot (Section 7), so it competes with other rainy-season upland crops. Avoid poorly drained paddy fields. A dry-season crop is possible only with autoflowering varieties and irrigation.
5. Pest and Disease Management
Hemp borer (Grapholita delineana) and hemp flea beetle (Psylliodes attenuatus) are documented mainly in Europe and Central Asia. Two-spotted spider mite (Tetranychus urticae) is the main pest of protected CBD crops in hot, dry conditions. Predatory mites (Phytoseiulus persimilis, Neoseiulus californicus) work best when introduced preventively.
Gray mold (Botrytis cinerea) is the most damaging disease in dense CBD flower. Prevention means wider spacing, removing lower foliage for airflow, and no overhead irrigation after flowering begins.
Root and stem rot is the main field problem in Thailand. HRDI found that coating seed with Streptomyces or Trichoderma harzianum reduced seedling death at 15 days by up to 77% and 49% respectively, compared with uncoated seed. Avoid sowing just before a period of heavy rain.
6. Harvest and Post-Harvest for CBD Hemp
6.1 Determining the Harvest Window
CBD and THC rise together as flowers mature (Section 2.2), so the harvest window is set by testing, not by appearance. NC State advises compliance sampling no later than about two weeks after floral initiation where a 0.3% limit applies. Under USDA rules, harvest must follow within 30 days of sampling. Testing by an approved laboratory documents compliance. It does not authorise selling flower where flower is a controlled product. In Thailand, flower remains a controlled herb (see the box above and bai251).
6.2 Drying
Flower must be dried quickly to below about 12% moisture to prevent botrytis and quality loss. Ambient-air drying is unreliable in humid Southeast Asian conditions; forced-air rooms or dryers are needed. Slow drying produces hay-like off-flavours and higher mould losses. In Thailand, handling, storing and selling hemp flower fall under the controlled-herb rules.
7. Hemp in Thailand: Regulatory and Practical Context
Licensing. Private licensing began under the Ministerial Regulation on licensing for the production, import, export, distribution or possession of Category 5 narcotics specifically for hemp, B.E. 2563 (2020), which took effect on 29 January 2021. Licences covered purposes such as study, research, breeding and certified-seed production. Seed was certified through registration with the Department of Agriculture, with THC test results submitted to the Thai FDA.
Varieties. The certified Thai varieties are domestic lines developed by HRDI with the Royal Project Foundation: RPF1, RPF2, RPF3 and RPF4. They were bred for fiber, registered with the Department of Agriculture in 2011 (B.E. 2554), and reported at about 0.2% THC. RPF1 suits highlands above 1,000 m; RPF3 suits 500–1,000 m.
Where it is grown. Press reports name Mae Sai (Chiang Rai), Phop Phra (Tak) and Song Khwae (Nan) as hemp areas. Hmong communities, notably in Phop Phra, have long grown hemp for textiles.
Planting calendar (northern Thailand, photoperiod RPF lines, per HRDI):
| Sowing | Outcome |
|---|---|
| Mar–May (only where water is available) | Long vegetative phase; plants can reach about 5 m, so wide spacing is needed |
| Jun–Jul (recommended; HRDI’s general window is May–Jul) | About 3 months vegetative growth, flowering late Sep–Oct, ~1 × 1 m spacing for seed |
| Aug–Feb (short days) | Short vegetative phase and early flowering; dense spacing (75 × 50 cm or closer) needed and biomass is low |
The dry season is therefore poor for photoperiod fiber hemp: short days trigger early flowering and low stalk yield. A dry-season crop needs autoflowering varieties plus irrigation. Avoid sowing just before heavy rain.
8. Regulatory Compliance and THC Testing
8.1 THC Limits by Region
| Jurisdiction | Plant THC limit (dry weight) | Notes |
|---|---|---|
| European Union | 0.3% (since 2023; previously 0.2%) | Certified varieties only |
| United States | 0.3% total THC (federal) | State/Tribal plans vary |
| Canada | 0.3% | — |
| Thailand | 1.0% in leaves and flowering tops; extracts ≤0.2% | Flower is a controlled herb; draft Act may change limits |
| Switzerland | 1.0% | — |
| United Kingdom | 0.2% | — |
8.2 Sampling Rules
- EU (Delegated Reg. (EU) 2022/126, Annex I): Under Procedure A, at least 30% of declared hemp areas are checked. Samples are taken from 20 days after flowering starts to 10 days after it ends, and consist of a 30 cm section with at least one female inflorescence from each of 50 plants per field. Under Procedure B, used with prior-approval systems, at least 20% of areas are checked. Samples are taken in the 10 days after flowering ends and consist of the upper third of 200 plants per field.
- USA (7 CFR 990.24 and USDA sampling guidelines): A sampling agent collects samples no more than 30 days before anticipated harvest by cutting the top 5–8 inches (≈13–20 cm) of the flowering top. States or Tribes may use a performance-based protocol, which must give 95% confidence that plants will not test above 0.3%. Plant counts per lot depend on the applicable plan.
- Thailand: Follow the sampling instructions of your licensing authority.
Do not pool a whole field into one sample, and keep a documented chain of custody. For a 0.3% limit, use about a 0.2% internal target (≈33% margin).
8.3 Records
Keep, for at least the period your licence requires: field maps with variety and lot IDs; seed invoices and certificates; input logs; sampling records with laboratory CoAs; and yields by block. Inspectors may compare seed purchased against the area planted.
Summary
Hemp success depends on matching the crop type (fiber, grain or CBD) to the available processing, choosing certified varieties suited to the latitude, keeping pH and nitrogen within one evidence-based range, and testing CBD hemp early because THC rises with maturity. In northern Thailand, photoperiod RPF varieties are sown at the start of the rainy season in well-drained fields. The dry season suits only autoflowering varieties with irrigation. Thai hemp flower remains a controlled herb, and the legal thresholds may change when the draft Cannabis Control Act is passed.
References
- Small, E. (2015). Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Journal of the Linnean Society, 180(1), 16–44.
- Amaducci, S., Zatta, A., Pelatti, F., & Venturi, G. (2008). Influence of agronomic factors on yield and quality of hemp (Cannabis sativa L.) fibre. Field Crops Research, 107(2), 161–169.
- Linger, P., Müssig, J., Fischer, H., & Kobert, J. (2002). Industrial hemp (Cannabis sativa L.) growing on heavy metal contaminated soil. Industrial Crops and Products, 16(1), 33–42.
- Faux, A. M., Draye, X., Lambert, R., d’Andrimont, R., Raulier, P., & Stilmant, D. (2013). The relationship of stem and seed yields to flowering phenology in monoecious hemp. European Journal of Agronomy, 47, 41–50.
- Schluttenhofer, C., & Yuan, L. (2017). Challenges towards revitalizing hemp: a multifaceted crop. Trends in Plant Science, 22(11), 917–929.
- Struik, P. C., Amaducci, S., Bullard, M. J., Stutterheim, N. C., Venturi, G., & Cromack, H. T. H. (2000). Agronomy of fibre hemp (Cannabis sativa L.) in Europe. Industrial Crops and Products, 11(2–3), 107–118.
- Rheay, H. T., Omondi, E. C., & Brewer, C. E. (2021). Potential of hemp (Cannabis sativa L.) for paired phytoremediation and bioenergy production. GCB Bioenergy, 13(4), 525–536.
- Development of cannabinoids in flowers of industrial hemp (Cannabis sativa L.): a pilot study (2020). Journal of Agricultural and Food Chemistry, 68(22), 6058–6064. pubmed.ncbi.nlm.nih.gov
- Suchoff, D., Linder, E., & Henriquez Inoa, S. (2022). Avoiding a hot crop: minimizing the risk of non-compliant THC tests through proper harvest timing. NC State Extension AG-937. Avoiding a "Hot" Crop: Minimizing the Risk of Non-compliant THC Tests through Proper Harvest Timing | NC State Extension Publications
- University of Wisconsin–Madison (2024). Cultivar Check Program final report. https://cropsandsoils.extension.wisc.edu/files/2025/03/2024-Cultivar-Check-Program-Final-Report-v5.pdf
- Rodale Institute. Growing industrial hemp as an organic cash crop. Growing Industrial Hemp as an Organic Cash Crop - Rodale Institute
- University of Delaware Extension (2020). Recommended nutrient rates, miscellaneous crops. https://udel.edu/content/dam/udelImages/canr/pdfs/extension/environmental-stewardship/nutrient-recommendations/UD_Extension_Recommended_2020_Misc_Crops_All.pdf
- Floral hemp (Cannabis sativa L.) responses to nitrogen fertilization under field conditions in the high desert. Floral hemp (Cannabis sativa L.) responses to nitrogen fertilization under field conditions in the high desert - PMC
- Commission Delegated Regulation (EU) 2022/126, Annex I. https://eur-lex.europa.eu/eli/reg_del/2022/126
- 7 CFR § 990.24, Sampling for THC. 7 CFR § 990.24 - Responsibility of a USDA licensee prior to harvest. | Electronic Code of Federal Regulations (e-CFR) | US Law | LII / Legal Information Institute
- HRDI (2022). ปลูกกัญชงผลิตเมล็ดเพื่อการบริโภค [Growing hemp for food seed]. ปลูกกัญชงผลิตเมล็ดเพื่อการบริโภค | สวพส.
- HRDI. ปลูกกัญชงอย่างไร…ให้รอด? [How to grow hemp so it survives]. ปลูกกัญชงอย่างไร…ให้รอด? | สวพส.
- Thai Publica (2021). HRDI hemp seed sales (RPF varieties). สถาบันวิจัยและพัฒนาพื้นที่สูง เปิดขาย "เมล็ดกัญชง2 พันธุ์" สั่งซื้อ 26 เม.ย. - 5 พ.ค.64 - ThaiPublica
- Nishimura & Asahi (2021). Thailand hemp regulation B.E. 2563 in force. https://www.nishimura.com/en/knowledge/publications/20210525-62786