24/0 Light Schedule: Pros and Cons

What 24/0 actually is

A 24/0 light schedule means the grow lights stay on 24 hours a day with zero hours of darkness during the vegetative stage. It's used as an alternative to the more common 18/6 (18 hours on, 6 off) or 20/4 schedules.

Cannabis is a short-day (photoperiod) plant: flowering is triggered by long nights, not by accumulated light hours. So photoperiod strains in veg won't flower under 24/0 — they'll keep growing vegetatively until you shorten the day length. Autoflowers, which flower based on age rather than photoperiod, can also be grown on 24/0 from seed to harvest Weak / limited^[1].

24/0 is not the same as "light stress." Cannabis, like most C3 crops, can photosynthesize continuously as long as CO₂, water, temperature, and nutrients keep up Strong evidence^[2].

Why growers use it (and what the evidence says)

Common claims for 24/0:

• Faster vegetative growth
• Higher yields
• Warmer tent (lights never off)
• Simpler — no timer needed
• Better for seedlings and clones

What actually holds up:

• Warmer tent: True. In cold basements or winter grows, continuous lighting keeps root-zone temperatures more stable. Strong evidence
• Simpler: True, but a $10 timer solves this.
• Seedlings and clones: Many propagators run 24/0 or 18/6 on low-intensity light because young plants benefit from steady, gentle light and warmth. Anecdote
• Faster growth / higher yield: Weak. Controlled horticultural research on cannabis and related crops generally shows that once daily light integral (DLI) is adequate, extending the photoperiod beyond ~18 hours gives diminishing or no returns, and can even cause problems in some species Weak / limited^[3][4].

The headline: you pay 25% more in electricity to run 24/0 vs 18/6, and in most side-by-side comparisons you don't get 25% more plant. Some growers report equal or better results on 18/6 because plants use the dark period for respiration, root growth, and hormonal cycling Weak / limited^[5].

When to start (and when not to)

Reasonable uses for 24/0:

• Seedlings under low-intensity light (T5, low-wattage LED)
• Rooting clones in a humidity dome
• Autoflowers, where some growers prefer 24/0, others 20/4 or 18/6 (no clear winner in the literature)
• Cold environments where you need the heat

Skip 24/0 if:

• Your tent runs hot (over ~28 °C / 82 °F). No dark period means no cooldown.
• You're paying premium electricity rates.
• You're running high-PPFD lighting where the plant is already saturated during 18 hours.
• You want to observe subtle stress signs — plants under 24/0 sometimes mask early problems until they're severe Anecdote.

How to run a 24/0 schedule, step by step

1. Confirm your strain type. Photoperiod plants can stay in veg indefinitely under 24/0. Autoflowers will flower on their own schedule regardless.
2. Check your environment. Measure tent temps with lights running continuously for 48 hours before committing. Aim for 22–28 °C (72–82 °F) leaf-surface temperature.
3. Set light intensity appropriately. For seedlings, keep PPFD around 100–300 µmol/m²/s. For established veg, 400–600 µmol/m²/s is plenty Strong evidence^[6].
4. Skip the timer, or use one anyway. A timer set to 24/0 gives you a fallback if you later want to switch to 18/6.
5. Monitor daily. Look for leaf curl (heat/light stress), pale new growth (nutrient burn from continuous uptake), and slow growth (root issues from no dark respiration cycle).
6. Transition to 12/12 for flower (photoperiod plants only). Drop straight from 24/0 to 12/12 — no need to step down gradually, though some growers prefer a 36–48 hour dark period first to encourage a cleaner flip Anecdote.
7. Track your kWh. Compare your electric bill to a previous 18/6 run. This is the only honest way to know if the extra hours are earning their keep.

Common mistakes

• Assuming 24/0 = more yield. It doesn't, reliably. Yield is driven by total DLI, genetics, environment, and nutrition — not by pushing photoperiod to the max Weak / limited^[3].
• Ignoring heat buildup. No dark period means no thermal recovery. Rooms creep warmer over days.
• Overfeeding. Continuous photosynthesis can mean continuous nutrient uptake. Growers who don't adjust EC downward sometimes see tip burn.
• Running 24/0 into flower on photoperiod plants. This won't happen because 24/0 blocks flowering — but growers occasionally forget to flip, then wonder why nothing is budding.
• Believing marketing copy. LED brands sometimes claim their fixtures "support 24/0 for maximum yields." That's marketing, not horticultural science.
• Skipping the timer. Power flickers happen. A timer keeps the schedule consistent through interruptions.

Related techniques

• 18/6 Light Schedule — the most common veg schedule and a reasonable default.
• 20/4 Light Schedule — middle ground.
• Autoflower Light Schedules — where the 24/0 vs 18/6 debate is most active.
• Daily Light Integral (DLI) — the metric that actually predicts growth, more than photoperiod alone.
• Vegetative Stage Basics — the wider context for these decisions.

Sources

How this page was made