Cannabis mother plants need 18 to 24 hours of light per day at 300 to 600 PPFD, with a 4000K to 6500K white spectrum. An 18/6 schedule keeps growth steady and cuts power use, while 24/0 pushes faster growth at a higher cost. Drop below 16 hours of light and the mother will start to flower.
cannabis mother plant cloning
What light schedule does a cannabis mother plant need?
A mother plant stays in vegetative growth, which means long days and short nights. The 18 hours on, 6 hours off schedule is the standard choice for stock plants. That dark window lets the plant rest and trims roughly a third off your power bill compared with round-the-clock light.
Cannabis Mother Plant Pest Control: Keep Moms Clean in Veg
20/4 and 24/0 both work if you want faster growth. Continuous light speeds up node stacking and clone production, but it also means more pruning, more water, and more heat to manage. Pick one schedule and hold it. Switching hours back and forth stresses the plant and slows rooting in the cuts you take.
cannabis mother plant cloning
- 18/6: balanced growth, lowest power draw, easiest to manage
- 20/4: slightly faster veg, moderate power use
- 24/0: fastest growth, highest cost, most maintenance
Never go under 16 hours of light. Cannabis measures the length of the dark period to decide when to flower, so a long night will flip a mother into bloom and end her usefulness as a stock plant.
How much light intensity does a mother plant need?
Aim for 300 to 600 PPFD at the top of the canopy. That range produces tight nodes, thick stems, and healthy cuttings without bleaching leaves or forcing constant trimming.
DLI math for mother plants
DLI (daily light integral) is the total light a plant receives in a day. You get it by multiplying PPFD by the number of light seconds, then dividing by one million. Mothers do well between 20 and 40 mol per square meter per day.
- 18/6 at 400 PPFD = 400 x 64,800 seconds / 1,000,000 = 25.9 mol/m²/day
- 24/0 at 300 PPFD = 300 x 86,400 seconds / 1,000,000 = 25.9 mol/m²/day
- 18/6 at 600 PPFD = 600 x 64,800 seconds / 1,000,000 = 38.9 mol/m²/day
Notice that a longer schedule with lower intensity can deliver the same DLI as a shorter schedule with more intensity. That gives you room to trade hours for watts. Push past 45 mol/m²/day and you risk leaf bleaching, burnt tips, and stalled growth.
Measuring light instead of guessing
A quantum sensor gives you PPFD numbers you can trust, and phone light meter apps work as a rough stand-in. Guessing by eye leads to two common outcomes: stretched plants under weak light, or scorched leaves under light that is too strong. Measure at canopy height, not at the fixture.
What spectrum keeps a mother plant healthy?
White light in the 4000K to 6500K range is the standard for stock plants. Blue-heavy output keeps internodes short and leaves thick, which makes cleaner cuttings and sturdier clones.
Full-spectrum LEDs with added blue handle mothers well. Red-heavy bloom spectrums push stretch, thinner leaves, and wider gaps between nodes, so save those for the flower room. If you run a dimmable fixture, dial intensity rather than changing the spectrum.
Some growers add a small dose of far-red at lights out. Research on stock plants is thin, so treat it as optional and test on one plant before you commit the whole room.
How far should the light be from the canopy?
Distance depends on fixture wattage, not on the plant size. Most LED panels sit 18 to 30 inches above the canopy to land in the 300 to 600 PPFD band. A 100 to 200 watt LED covers a 2x2 to 3x3 foot mother area at that height.
Read the plant for feedback. Raise the fixture if leaves cup, bleach at the tips, or curl at the edges. Lower it if new growth stretches with long gaps between nodes.
LED vs HID vs fluorescent for mother plants
- LED: low heat, low power draw, long lifespan, easy dimming
- Metal halide (HID): strong blue output, cheap upfront, runs hot and needs more clearance
- T5 fluorescent: fine for small mothers and clones, low intensity, sits close to the canopy
Most home growers now run dimmable LEDs because the heat load stays low in a small tent. Heat matters for mothers. Warm rooms push stretch and make clones harder to root.
Do light leaks matter for mother plants?
Mothers run on long days, so a brief light leak during the dark window causes less harm than it would in flower. Repeated interruptions to the dark period can still trigger odd growth, slow rooting, and uneven cuttings.
The bigger risk runs the other way. If you keep mothers and flowering plants in one room, light from the veg area can leak into the flower space and cause hermaphrodites. Use separate tents or a sealed partition.
How do you use light to control mother plant growth?
Light level is your main throttle on how fast a mother grows. Higher PPFD and higher DLI mean faster growth and more frequent pruning. Lower light slows growth and stretches the time between cuts.
Many growers keep mothers at the low end of the range, around 300 to 400 PPFD, on purpose. Slower growth means less maintenance and less plant material to throw away. If you need cuttings fast, raise PPFD to 500 or 600 and keep room temps in the mid 70s.
Common mother plant lighting mistakes
- Running a red-heavy bloom spectrum in the veg room
- Letting the schedule drift below 16 hours of light
- Allowing the canopy to grow into the fixture
- Skipping light measurement and relying on height alone
- Changing schedules every few weeks
- Keeping mothers and flowering plants in one open room
Mother plant lighting FAQ
Can a mother plant stay under 24 hours of light?
Yes. Cannabis is a perennial that can grow under continuous light for months. The trade-offs are higher power bills, more heat, and faster growth that needs more pruning.
Does a mother plant need a dark period?
No, but most growers use one. A 6-hour dark window lowers costs and gives the plant a rest cycle without changing the veg state.
Can I keep a mother plant under 12/12?
No. A 12-hour dark period triggers flowering, and once a mother flowers she stops producing vegetative cuttings. Keep the dark period at 6 hours or less.
What PPFD is too much for a mother plant?
Sustained PPFD above 700 without added CO2 and dialed-in temps tends to bleach leaves and stall growth. Stay under 600 for stock plants unless you test on one plant first.