The First Two Weeks of Flower

When and how to flip

Photoperiod plants flip to 12/12 light when size and training are where you want them — they often double or triple in height during stretch. Flip early if ceiling height is tight; flip late if you want a bigger frame first.

Switch timer to 12 hours uninterrupted darkness. Light leaks during dark period cause hermies and reveg stress — seal tent zippers and LED indicator tape on equipment.

Stretch: weeks 1–2 of flower

Most stretch happens in the first 2–3 weeks after flip. Sativa-leaning strains can explode vertically; indicas stretch less but still pack nodes.

Raise light as tops grow. Re-tie LST daily if needed. SCROG growers weave new growth under the screen until stretch slows around week 3–4.

• Week 1: explosive vertical growth, preflowers appear
• Week 2: stretch continues, bud sites form at nodes
• Week 3+: vertical growth slows, bud swell begins

Nutrient transition

Gradually shift from grow to bloom formula over 7–14 days — don't slam nitrogen off overnight unless your line specifies a hard switch. Lower nitrogen too fast yellows lower leaves aggressively.

Increase phosphorus and potassium as stretch ends. Watch new growth color — pale tips mean back off; dark green claw means too much nitrogen still.

Defoliation in early flower

Strategic defoliation in weeks 1–3 opens airflow before buds densify. Remove fans that shade bud sites, touch soil, or block under-canopy air — not every leaf on the plant.

Controversial online, optional in practice. If you defoliate, do it in stages across days, not one brutal strip. Autoflowers tolerate less than photoperiod.

Environment adjustments

Start lowering RH as buds form — 50% by week 3, trending toward 40–45% late. Increase airflow as canopy mass builds.

Watch for stretch-induced humidity spikes — transpiration jumps when leaf surface area explodes.