Typical Timeline for Bud Swelling

Weeks 1–2 of Flowering: Flower Initiation

Plants transition from vegetative growth to flowering.

You will see white pistils (hairs) forming at nodes.

Bud sites are established, but there is little to no swelling yet.

Weeks 3–4: Early Bud Formation

Small bud clusters start to form.

Vertical stretch slows or stops.

Buds become more defined, but still relatively airy.

Swelling is minimal and often uneven.

Weeks 5–7: Major Bud Swelling Phase

This is when most bud mass is built.

Calyxes expand and stack.

Buds become denser and heavier.

Trichome production increases rapidly.

This stage accounts for a large percentage of final yield.

Weeks 8+: Final Swell and Ripening (Strain-Dependent)

Many strains show a final “bulk-up” swell in the last 1–2 weeks.

Pistils darken and recede.

Calyxes swell further as the plant finishes.

Resin matures rather than increasing dramatically in volume.

Factors That Strongly Affect Bud Swelling

If buds are not swelling as expected, the cause is usually environmental rather than genetic.

1. Light Intensity

Insufficient PPFD will limit bud density.

Flowering typically requires 600–900+ PPFD depending on cultivar.

2. Temperature & VPD

Ideal flower temperatures: 20–26°C (68–79°F)

Poor VPD (especially high humidity) reduces transpiration and nutrient uptake.

3. Humidity Control

Mid–late flower RH should generally be 40–50%.

High humidity often leads to leafy, underdeveloped buds.

4. Nutrition

Excess nitrogen in flower delays bud stacking.

Adequate potassium and phosphorus support calyx expansion.

Lockout from pH or EC issues can stall swelling.

5. Genetics

Some cultivars swell late and rapidly; others build steadily.

Indica-dominant strains often swell earlier than sativas.

Common Misconception

Practical Takeaway

Expect visible bud swelling around weeks 4–5 of flowering

Peak swelling occurs weeks 5–7

Final size is heavily influenced by light, humidity, temperature, and nutrient balance