Cannabis Flowering Stage: Duration, Care & Harvest Time

The Cannabis Flowering Stage: The Ultimate Guide

The flowering stage is the most exciting and at the same time the most demanding part of the cannabis plant’s life cycle: this is when inconspicuous green shoots turn into dense, resinous buds. If you understand what happens in this phase and what matters, you lay the foundation for a high-quality harvest. In this article you’ll learn when flowering starts, which stages it includes, which conditions are ideal now and how to recognise the perfect time to harvest.

The advice applies to plants from cannabis seeds as well as to hemp clones.

What is the flowering stage?

The flowering stage is the final, reproductive phase in the cannabis life cycle. In nature it’s triggered by the shorter days of late summer – a signal for the plant to reproduce before winter. Unlike the vegetative phase, where size and leaf mass take priority, during flowering the plant focuses all its energy on forming the female flower clusters that later become the buds.

When does flowering begin?

Photoperiod strains: as soon as the indoor light cycle is switched from 18 to 12 hours of light – outdoors the process starts automatically after the summer solstice, as the days get shorter. Autoflowering strains: independent of light, purely based on age, usually 3–6 weeks after germination.

After the switch, it usually takes 2–3 weeks for the first visible signs of flowering to appear.

The three stages of flowering

1. Early flowering (weeks 1–3)

The plant stretches noticeably once more (“the stretch”), forms its first flower sites (pistils) and sets the basic structure for the buds to come.

2. Mid flowering (weeks 4–6)

Vertical growth stops, the buds thicken noticeably and resin production visibly increases. This is where it’s largely decided how dense and compact the final flowers will be.

3. Late flowering / ripening (week 7 to harvest)

The buds keep filling out, the pistils turn brown and the trichomes – the resinous gland heads – change colour, signalling the time to harvest.

In total, the flowering stage lasts between 7 and 14 weeks depending on genetics; feminised strains average around 9 weeks, and indica-dominant strains tend to finish faster than sativa-dominant ones.

Optimal conditions during flowering

Factor	Recommendation
Light cycle	12 h light / 12 h darkness (photoperiod)
Temperature	Approx. 26 °C during the day, dropping towards 20–24 °C by harvest; cooler at night
Humidity	Gradually falls from around 50–65% in mid flowering to approx. 40% towards the end to prevent mould
Nutrients	Less nitrogen, more phosphorus and potassium (classic bloom fertiliser)
pH (irrigation water)	Around 6.0–6.5
Air circulation	Constant and good, to prevent Botrytis (bud rot)

A good rule of thumb: the closer harvest gets, the drier and slightly cooler the climate in your tent or greenhouse should be – this protects dense buds from mould.

Trichomes: how to recognise the right time to harvest

The most reliable indicator of ripeness isn’t the brown hairs (pistils), but the trichomes – the tiny resin glands on the flowers. They’re best checked with a magnifying loupe or a USB microscope (30–60x magnification):

Clear/transparent → still unripe, THC build-up is just getting started
Milky white → THC content at its peak, more energetic, clear-headed effect
Amber → THC slowly converts to CBN, the effect becomes more body-focused and relaxing

As a rough guide: harvest when around 70–90% of the trichomes are milky white and a smaller share (about 10–30%) has already turned amber. Worth knowing: amber doesn’t automatically mean “stronger”, just “later” – too much amber tends to break down valuable THC rather than intensify the effect.

Common mistakes during flowering

Too much nitrogen even in late flowering – delays ripening and can affect the taste
Humidity too high with dense buds – encourages mould and bud rot
Harvesting too early because the pistils already look brownish, even though the trichomes are still clear
Neglecting light-proofing – even small light leaks during the dark period can stress photoperiod plants and trigger hermaphroditism

Conclusion

The flowering stage is when all your earlier care pays off. With the right light cycle, adjusted feeding, a stable climate and a trained eye on the trichomes, you can follow week by week how the buds develop – and plan the harvest precisely.

That’s how you lay the foundation for aromatic CBD flowers and a high-quality harvest.

Sources

Note: this article is for general information about plant cultivation only. Please observe the laws on growing and possessing cannabis that apply in your country or canton.