Field · special crop

Industrial hemp in the field

A practical guide to growing industrial hemp (fibre and seed/oil hemp) outdoors in Finland: law and notifications, variety, sowing, fertilising, the season and harvest. Covers approved varieties only, field cultivation, and fibre (stem) and seed.

StartFirst step: mark hemp on a parcel.

What industrial hemp is

An annual field crop grown for stem fibre or for seed (oil hemp) – or both.
Fibre hemp grows 2–4 m tall, 112–141 days. Finnish trials: typically 4–8 t DM/ha, of which 1–2 t/ha fibre.
Oil hemp (e.g. Finola) is short and grown like turnip rape. Seed yields in Finland usually 600–1000 kg/ha, organic below 500 kg/ha.
Fibre goes to composites, insulation and textiles; shives to bedding. Seed goes to oil and food.
The deep taproot improves soil structure – a good break crop.

⚖️ Law and notifications

You may grow hemp in the field when all of these are met:

The variety is in the EU Common Catalogue and eligible for aid – THC max 0.3 %.
Sow certified seed only. Farm-saved or uncertified seed is not eligible. Seed bought online must be certified too.
Only one hemp variety per parcel (no variety blends or mixed crops).
In the area aid application (Vipu), declare the seed rate (kg/ha) and planned sowing date.
Submit the certification labels of every seed bag to Vipu or the municipality by the deadline – 9 June in 2026. Late or incomplete = no aid for any hemp area.
Keep the original labels for the application year plus 4 years.
The authority may take a THC sample in July–September, from 20 days after flowering starts to 10 days after it ends (Finola: 55–75 days after sowing).
Keep the crop until sampling: harvest no earlier than 10 days after flowering ends.

This guide covers fibre and seed production only. Harvesting flowers or leaves for use is not part of this guide. Rules and dates change yearly – check the Finnish Food Authority guide.

Choosing a variety

Decide first: seed (combined) or fibre (stems harvested).
Seed: Finola is a Finnish-bred oil hemp and practically the only one grown (99 % of area in 2017). Short and easier to combine – not a fibre variety.
Fibre: Finnish trials have used e.g. Uso 31. Always check that the variety is in that year's EU catalogue and eligible.
A variety loses eligibility if its average THC exceeds 0.3 % two years in a row – check the list every spring.
Buy from a reliable seller with certification labels. Hemp is often a contract crop – find a buyer before sowing.

Field and soil

Best: humus-rich, moist, loose, well-drained soil. Fibre hemp suits light fine-sand and clay soils.
pH target: 6–7 for oil hemp, above 5.6 for fibre hemp.
Avoid compacted clay, wet hollows and drought-prone fields. Seedlings under 3 weeks suffer from waterlogging.
Pick a low-weed field – there are hardly any herbicides for hemp.
Good preceding crops: faba bean, lucerne, clover, fallow; also grass and root crops.
Rotation of at least 4 years without hemp, rape, faba bean and sunflower (Sclerotinia).
Autumn ploughing is recommended for fibre hemp. Shallow spring seedbed, conserving moisture.

Sowing

Sow into warm, moist soil. Sowing too deep is the most common cause of failure.

	Seed (oil hemp, e.g. Finola)	Fibre (e.g. Uso 31)
Soil temperature	8–10 °C	8–10 °C
Sowing time	May, around mid-month (southern Finland), by conditions	Early spring, by mid-June at the latest
Seed rate	25–30 kg/ha (first-timers 30–35; direct drilling ~30 kg/ha)	25–60 kg/ha by variety – check with seller
Target density	about 100 plants/m²	denser = thinner stems, finer fibre
Depth	1–2 cm (dry soil 2–3 cm)	1–3 cm
Row spacing	12.5–25 cm	standard cereal drill, e.g. 12.5 cm

Shallow, even seedbed. Rolling before sowing keeps seed from going too deep.
Emergence in 4–7 days in warm, moist soil.
Seedlings tolerate light frost, but a cold early summer slows growth.
Record sowing date and seed rate – they go into the aid application.

Dense hemp crop in a field — Hemp crop in late summerPhoto: Ben Skála (Benfoto) · CC BY-SA 4.0

Tractor and mower harvesting hemp — Harvest: mowing and swathingPhoto: Aleks · CC BY-SA 3.0

Fertilising

Fertilise by soil test. Cereal fertilisers and organic fertilisers work.
Fibre hemp: 60–110 kg N/ha by humus content, 20–30 kg P/ha (limit 0–30 kg/ha by soil class) and 60–100 kg K/ha.
Too much nitrogen lowers fibre quality.
Oil hemp: about 60–80 kg N/ha. More N makes the crop taller and delays and complicates combining.
N/K imbalance can increase lodging.
Environmental scheme or organic limits may be stricter – check with ProAgria / the Finnish Food Authority.

Season: weeds, birds, monitoring

A good start is the best weed control: even, dense emergence. At 3–4 weeks (~30 cm) hemp already shades most of the ground.
Sparse stands let weeds through. Use plant protection products only if approved for hemp – check the Tukes register.
Pests have hardly been an issue in Finland. Wet autumns bring grey mould and Sclerotinia – especially on small, forest-sheltered fields.
Hemp needs about 250–400 mm of water per season; most in July and during seed set.
Record the start of flowering: it sets the THC sampling window and earliest harvest date.
Birds go for ripe seed in late summer and autumn – when flocks appear, combining is near.
Storms and hail can flatten tall crops. Check the field after storms.

Harvest: seed and fibre

Seed (oil hemp)

Growing time about 120–130 days, longer in cool summers.
Combine when seeds start to shed: ~70 % ripe, moisture ~22–30 %. Late harvest = shedding and bird losses.
Header as high as possible, sharp knives. Fibres wrap around moving parts; fibre in bearings causes heat and fire risk.
Drive steadily and clean bearings and shafts often.
Avoid cracking seed: oily seed goes rancid easily.
Stems can be chopped into the field during or after combining.

Fibre (stem)

In Finland fibre hemp is usually harvested in spring right after snowmelt while the ground is still frozen (dry-line method).
Autumn harvest suffers from wet weather and high drying costs.
Baling: large square balers have worked best, round balers reasonably; small balers clog.
Flail mowers and other rotating blades clog easily on tough stems.
Agree fibre delivery and quality requirements with the buyer before sowing.

Drying, storage and retting

Seed: start drying within 3–4 hours of combining. Dry to 7–9 % moisture.
Drying air max 30 °C. Flatbed and cold-air dryers work; turn the crop so a moist top layer does not form.
Clean with sieve and air cleaners. Buckwheat and some weed seeds are tricky – clean several times if needed.
Store at 7–9 % moisture, protected from birds and rodents. Good seed keeps 2–3 years.
Remember: do not sow your own harvest – buy certified seed again next spring.
Fibre: winter freeze–thaw does the retting in the field (field/winter retting), so fibre separates more easily in spring.
Keep bales dry. Decortication is done on a mechanical line at the buyer or processor.

Season checklist

Winter

Choose the use and agree a buyer.
Check eligible varieties and order certified seed.
Pick a low-weed, well-drained field; check the soil test.

Spring (Apr–May)

Area aid application in Vipu: hemp, variety, seed kg/ha and planned sowing date.
Keep seed bag labels.
Fibre: harvest last year's crop right after snowmelt.

May–June

Sow into 8–10 °C soil, 1–2 cm deep.
Labels to Vipu or municipality by the deadline (2026: 9 June).
Watch emergence and weeds.

Summer (Jun–Jul)

Record start of flowering.
Leave the crop intact – THC sampling possible July–September.
Check the field after storms.

Aug–Sep

Watch seed ripening and birds.
Combine no earlier than 10 days after flowering ends, when seeds start to shed.
Dryer ready: drying within 3–4 h.

Autumn

Dry seed to 7–9 %, clean and store protected.
Chop oil hemp stems into the field; fibre hemp stays out over winter to ret.
Keep labels and notes (4 years).

Figures are recommendations and ranges from Finnish sources. Your soil test, the seed seller's instructions and ProAgria advice always come first.