How is hemp grown? From sowing to harvest

Hemp is grown from seed sown in spring in loose, well-drained soil; it starts to flower as the days get shorter and is harvested after about three to four months. Farmers time the harvest to the crop: fibre hemp is cut around flowering, grain hemp when most seeds are ripe, and CBD hemp when the flowers are mature. In the UK, growing hemp needs a Home Office licence, and only the seeds, fibre and mature stalk may be used.

How is hemp grown, step by step?

1. Choose the variety and seed. The variety depends on the goal: fibre, grain (seed) or flowers for CBD. In the EU, farm payments require certified seed of a variety listed in the Common Catalogue whose THC content stayed within the limit (Regulation (EU) 2022/126, Art. 2).
2. Prepare the soil. Hemp does best in well-drained loam with a pH of 6.0–7.5. (Ontario).
3. Sow. Sow 2–3 cm deep in late spring. Fibre crops are sown densely (about 200–250 plants per m²) so the stems grow tall and thin. Grain crops are sown more thinly (100–150 plants per m²).
4. Let it grow. A dense crop shades about 90% of the ground within 3–4 weeks and suppresses nearly all weeds.
5. Flowering. Four to five weeks after midsummer, the shortening days slow leaf growth and trigger flowering.
6. Harvest and dry. The timing and the machines depend on the product (see below), and the crop is dried after harvest.

How long does it take to grow hemp?

In Ontario's field guidance, fibre hemp is ready about 70–90 days after sowing, during pollination. Grain hemp takes about 100–120 days and is harvested when about 70% of the seed is ripe (Ontario). Flower crops for CBD follow the variety's flowering time.

The exception is photoperiod-insensitive ("autoflowering") hemp, which flowers by age rather than day length. Researchers have mapped at least two separate genetic regions behind this trait (Toth 2022; Dowling 2024). Read more in what is Cannabis ruderalis?

Is hemp grown outdoors, in greenhouses or indoors?

All three. Most fibre and grain hemp grows in open fields. Hemp grown for CBD flowers is also grown under cover, where light, water and rain exposure can be controlled.

Our hemp is grown in Central Switzerland. The outdoor crop is mainly used for our CBD oils, and greenhouse hemp is mainly used for flowers. You can read how the plant becomes an oil in how CBD is extracted from hemp.

What climate does hemp need?

Hemp grows in a wide range of temperate climates, but it is fussy about water at two moments. Young plants are very sensitive to wet soils or flooding during their first three weeks, and drought during flowering and seed set reduces yields. Ontario's guidance puts the ideal at 300–400 mm of rain over the season (Ontario).

Moisture at the end of the season is the other risk: white mould (Sclerotinia) and grey mould (Botrytis) are among the main diseases.

Is hemp hard to grow?

The plant itself is fairly easy: it grows fast, shades out weeds, and according to the European Commission, insecticides, herbicides and fungicides can be avoided in most cases (European Commission). The harder parts are:

• The rules. Approved varieties, certified seed and THC checks during flowering. In the EU, authorities sample fields from 20 days after flowering starts to 10 days after it ends (how hemp is tested for THC). In the UK, it is an offence to grow any cannabis plant without a Home Office licence. Industrial hemp licences cover approved varieties with no more than 0.2% THC and the use of "seeds and fibre/ mature stalk only", because the leaves and flowers are controlled parts of the plant (Home Office 2025). In Switzerland, hemp must stay below 1% THC to fall outside the Narcotics Act (FOPH).
• The weather. Waterlogged soil early on, drought at flowering, or heavy rain before harvest can cost a crop.
• The harvest. Fibre, grain and flowers each need their own timing and equipment.

How is hemp harvested?

• Fibre: cut during pollination, then usually left in the field for 14–21 days to "ret". Microbes loosen the fibres from the woody core during this time, and the fibres are later separated by decortication.
• Grain: combined when about 70% of the seed is ripe, at 22–30% moisture, then dried.
• Flowers for CBD: harvested when the flowers are mature, then dried gently. The cannabinoids sit mainly in the resin glands of the female flowers.

After harvest, the THC in the crop still matters. Our guide to THC testing explains how labs measure it.

Is hemp good for the environment?

It has real advantages, though the result depends on the farm. According to the European Commission, one hectare of hemp stores 9–15 tonnes of CO₂. Hemp also helps break disease cycles in a crop rotation, and its fast cover suppresses weeds (European Commission). Fertiliser and water needs still depend on the soil, climate and crop.

From Swiss hemp to the bottle: our CBD oils.