Excessive stretch after the flip (more than about 3x)

Likely causes, most likely first

Ranked for this sign on its own. Your stage, medium and readings change the order, so run the checker for your plant.

1. PossibleLong-flowering or light-sensitive cultivar

   GeneticsLow urgencyRead: The flip isn't day 1 of flower: the 10–14 day transition and how to count it

   Fix: After the flip there is a 10-14 day transition before flowering really starts (up to 3 weeks in slow cultivars). Count from the flip and add the transition; flip earlier or train flatter for big-stretch cultivars.

   Recovery: Pistils at the top of the main stem by about 3 weeks after the flip.

   How to confirm it

   • Check for light leaks in the dark period. Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off.
   • Compare with siblings or the same cut. Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed.

2. PossibleNormal stretch after the flip

   Normal ageingLow urgencyRead: Stretchy, leggy cannabis: a differential

   Fix: Most cultivars grow 1.5-3x in the first 2-3 weeks after the flip. Plan height before the flip; supercrop or LST through it.

   Recovery: Stretch stops by about weeks 3-4 of flower.

   How to confirm it

   • Measure PPFD at the canopy top. Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little.

3. Less likelyNot enough light

   LightLow urgencyRead: Stretchy, leggy cannabis: a differential

   Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat.

   Recovery: New internodes shorten within a week; denser buds on the following weeks of growth.

   How to confirm it

   • Measure PPFD at the canopy top. Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little.

Look for

Height log from flip day, light distance and PPFD..