Internode Length and Stem Control for Growing Scrog
Physiology levers (what actually changes internode length)
Blue fraction (400–500 nm) → tighter nodes.
Blue light suppresses stem elongation across many species (cryptochrome/phototropin signaling). This is the basis for “compact mode.”
Far-red (∼700–750 nm) and low R:FR → stretch.
Far-red increases internode length and overall extension growth (classic shade-avoidance via phytochrome). This supports our “stretch mode” and the end-of-day FR trick
Temperature & DIF (day–night delta) → strong morphology knob.
Positive DIF (warmer day than night) increases stem elongation; zero or negative DIF suppresses it. That directly underpins the “warmer = stretch, cooler = compact” lines. Mechanistically, warm temps drive thermomorphogenesis via PIF4College+4
End-of-day far-red pulse → adds stretch.
EOD-FR is a well-documented way to enhance elongation; typical research pulses range 10–60 min. Our suggestion to start at 10–15 min is a conservative operational point inside that window.
________________________________________
DIF = Difference in Day and Night Temperature.
It’s a horticultural control lever for plant architecture:
• Positive DIF (day temp higher than night temp) → stems elongate more, internodes stretch.
• Zero DIF (same day and night temp) → neutral effect, moderate elongation.
• Negative DIF (day temp cooler than night temp) → stems shorten, internodes stack tightly.
Mechanism: temperature cycles influence growth hormones (gibberellins, auxins) and phytochrome signaling. Warmer days relative to nights stimulate elongation; cooler days suppress it.
In practice for cannabis:
• If you want compact plants, run a slightly cooler day temp (22–24 °C) and let nights dip 1–3 °C cooler.
• If you want stretch, flatten that difference or even keep nights equal/warmer than days.
This is one of the fastest-acting “knobs” — stem elongation shifts within 24–72 hours of changing DIF.
Here’s the Autoflower DIF Recipes — hard-number temperature schedules you can run alongside your PPFD/spectrum dials. This gives you the fastest way to “stretch or stack at will,” since DIF works within 1–3 days.
________________________________________
Autoflower DIF Protocols (Internode Spacing Control)
1. Compact Mode (tight stacking)
• Day Temp: 22–24 °C (72–75 °F)
• Night Temp: 19–22 °C (66–72 °F)
• DIF: –2 to –3 °C (day cooler than night)
• Result: Suppresses stem elongation, nodes stack tightly. Internodes can be held to ~1 in or less.
• Use when: Sativa-leaning autos, tents with limited vertical space, or when you want baseball-bat colas.
________________________________________
2. Neutral Mode (balanced, hybrid-friendly)
• Day Temp: 23–25 °C (73–77 °F)
• Night Temp: 22–24 °C (72–75 °F)
• DIF: ~0 °C (same day/night)
• Result: Normal growth, moderate internode spacing (1–2 in).
• Use when: Hybrids or mixed runs where you just want steady growth without extremes.
________________________________________
3. Stretch Mode (increase spacing)
• Day Temp: 26–28 °C (78–82 °F)
• Night Temp: 26–28 °C (78–82 °F)
• DIF: +1 to +2 °C (day equal or slightly warmer than night)
• Result: Actively stimulates elongation; internodes extend 2–3 in.
• Use when: Indica-dominant autos that squat too hard, or when you need to fill vertical canopy space early.
________________________________________
Timing Notes
• DIF effects are fast: visible elongation or suppression in 2–3 days.
• You only have Week 2–5 window in autos to really influence architecture; after pistils set, internode length is basically locked.
• Combine DIF with light spectrum control: Blue+negative DIF = maximum compaction. Red/FR+positive DIF = maximum stretch.
________________________________________
Factors Controlling Internodal Spacing (Ranked)
1. Light Spectrum (Blue vs Red/Far-Red balance)
• Most powerful single lever.
• Blue (400–500 nm) suppresses elongation → compact nodes.
• Red + far-red (660–750 nm, low R:FR ratio) stimulates elongation → stretch.
• This is phytochrome-driven (shade avoidance) and cryptochrome-linked.
• Acts fast (24–48 h), very reliable.
Order: #1
________________________________________
2. DIF (Day–Night Temperature Difference)
• Second strongest lever.
• Negative DIF (day cooler than night) → short internodes.
• Positive DIF (day warmer or equal to night) → elongated internodes.
• Acts via hormone signaling (gibberellin/auxin) and thermomorphogenesis (PIF4).
• Effects visible in 2–3 days, strong and consistent.
Order: #2
________________________________________
3. Light Intensity (PPFD/DLI)
• Moderate but important.
• High PPFD (with adequate nutrients) compacts plants: strong photosynthesis, less shade avoidance.
• Low PPFD early → stretch (plants “reach” for light).
• Works best in combination with spectrum.
Order: #3
________________________________________
4. Absolute Temperature (not just DIF)
• Warm canopies (26–30 °C) encourage elongation.
• Cooler canopies (20–23 °C) suppress elongation.
• Independent of DIF, but weaker effect than the differential.
Order: #4
________________________________________
5. Photoperiod Duration (Hours of Light)
• In autos, fixed long days (18–20 h) are standard.
• Very short days increase elongation in many crops, but not usually relevant for autos since you don’t cut light back.
• Minor effect relative to spectrum + DIF.
Order: #5
________________________________________
6. Nutrients (esp. Nitrogen form)
• Excess ammonium or nitrate can stimulate elongation in some crops.
• In cannabis, not a reliable primary lever for internode control. Manage N for vigor and leaf expansion, not stem length.
Order: #6 (weakest)
NOTE: This is from a 17-page discussion on CHATGPT5 paid about increasing/decreasing internodes at will on autoflower cannabis, with facts sources and numbers re-checked. I was interested in decreasing stem length for leggy cultivars indoors. Also photos before setting outside. Your mileage and phenos may vary. All disclaimers applied here
is it easier on an actual computer?
