How many hours of light do you use when starting indoors?

New to growing and have been messing around with starting various companion flowers and herbs indoors.

Strain is Sweet Blue Lilac (Blue Dream x Huckleberry Soda) standard photo-period.

I have a 32W Full Spectrum 2ft LED from Byingo. Enough for 2 or 4 small containers to start indoors.

When they sprout and I remove the condensation cover, how many hours do I leave the light on for?

I believe they need to be moved outside at roughly 13hrs+ of daylight?

I installed an app called SolarWatch that should let me know which day/week that is as it gets closer.

Any help and guidance much appreciated!


I start off at 20/4 at low light level.
I back off to 18/6 about node 3 and increase the light level.
Outdoors the days will be increasing in length until Summer Solstice, (June 21) then they start to shorten.

I’ll let others with better experience tell you when it is best to move them outdoors.



20/4 sounds like a good schedule.

I end up using 24/0 on clones and seeds.

Once things are going I back down to 18/6 - around 3 or 4th node, or when clones are well rooted after initial transplant into rockwool.


I veg 3-4 weeks when running regular photoperiod seed on 24 hours light then I switch it back to 18 and most my males will show
If I’m running female seed or cuttings I go straight 18. If you wait until June 1st to plant I’ve never had a problem. 2 weeks earlier and your plants may start to flower then have to revert back costing growth. That’s my 2 cents… good luck


I use 16/8. Sometimes 24/0 if I’m too lazy to set a timer.


I usually go 16-18. 16 works fine if I am trying to save a little on electric.


Never thought to do 24 straight (even on autos even though I know some people do). Do you feel like it speeds up growth any?

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I dont think it really speeds things up. I just have it on 24 for clones and my seedlings go in the same tent.


I have always used 24/0 for vegging usually a month. Then 12/12 for flower. I have always and probably will grow autos 24/0. And that’s true autos. These methods have always treated me well. Also 24/0 for clones/ seedlings.



cloning - 24hr (keeps my heat consistent)
veg - 18/6
flower 12/12


24/0 if its cold, and 16/8 if the night is not below 68f


24/0, then to 20/4 then to 18/6, then to either 12/12 or 10/14 if long flowering sativa’s.


18/6 usually, but trying 24/0 this grow. My plants seem to be growing faster, but they have some wavy leaves. Might have to give them some darkness.

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Hi, Dr. Zinko of Seven Trees here. I breed autoflowers and photoperiods. I’d like to talk seed starting light cycles, in the context of breeding new autoflowering lines from intercrossed photoperiod genetics.

When testing a F1 cross of an Autoflower x Photoperiod genetic, I use this light regime:
-24hours light throughout period of emergence; typically 3-5 days
-12/12 until sex is shown; all females up-potted, males segregated
-Sexed plants exposed to 24hrs light indefinitely

This process encourages uniformity in early seedling stage development, which correlates to uniformity in sexual maturation; identifies gender early through photoperiodic influence and root space constraint, then provides opportunity to segregate photoperiod (which continue vegetatively) and day-neutral (which flower automatically) expressions.

However, if starting seed under 12/12, several problems arise:
-A seedling may emerge in the final moments of a light period; no chlorophyll is developed for 12 hours, and the next light period communicates photons which are not as efficiently utilized. The effect is exponential and can cause days separation in sexual maturity even among uniform, true breeding plants. Additionally, the potential for opportunistic pathogens to strike developing seedlings is reduced with light exposure and its consequence of active growth; a growing seedling, and well-lit soil cannot harbor the same broad range of pathogens as which may propagate in a 12-hour dark period.
-In the early identification of sex, both day neutral and photoperiodic expressions will be selected without differentiation. The determination between the two cannot be made without an attempt to maintain vegetative growth. This is because (under a flowering light cycle) both auto. and photo. expressions of the same progenitor(s) are highly likely to determine sex and develop floral clusters in identic fashion and timing; there is no way to tell the difference, because they will both flower similarly under 12/12.

In first hand experience, I have seen too that F1 progeny from Auto x Photo crosses may show autoflowering dominance. It is folly to assume that all individual progenitors of all photoperiod plants will carry dominant traits. Mendelian genetics is a tool for comprehension of trends in populations observed, but is by no means a rule or reflection of the organizational intelligence of DNA and its relative expressions. I have used repeatedly the day-neutral pollen from a sole autoflowering male, which can be thought of as “dominant” in day neutral expression; all photoperiod females it has pollinated have produced 100% autoflowering or 75% autoflowering F1 progeny.

If we consider Time and Resources in the context of the aims set forth in a breeding project, it is ideal to identify from larger populations which initial selections will be made. For pursuit in stabilization of a day-neutral trait within a line, the most advantageous mechanism for traction in life-long breeding efficiency and productivity is the cultural means to determine sexing; where early sexing promotes consecutive turnovers of compounding value, and prolonged vegetative growth or root mass accumulated in culled plants extols resources; most valuable of which is time.

Further, a longer day-length, such as 18, 20, or 24 hours of light exposure, promotes more vigorous growth. By providing increased photon availability, the plant grows at an increased rate compared to a 12/12 light cycle. This growth presents exponential gains in metabolic processes, including sexual maturation. Simply put: autoflowers will sexually mature, transition, flower, and be ready for harvest sooner under a 24on light cycle than a 20/4 or 18/6 or 12/12.

Because the economics of business are such: that an increase in investment, provides an increase in return, we can see that the resources of time and even money are most respected when providing for the plant an environment which encourages fastest growth potential. The immediate financial return in seed weight, the traction in long-term progression of breeding goals, and the certainty of excluding photoperiod genetics from inclusion are all reasons to eschew a 12/12 flowering cycle from seed in selecting autoflowering expressions.

-Dr. Zinko


Having said that, one of my favorite things to grow photoperiod seed from 12/12. I often find equal speed of maturation, with greater yield and quality in growing photoperiods of great genetics from seed under 12/12, compared to autoflowers of dubious origin grown at 24 or 20 hours of light.

I do observe that 24 hours of light produces larger plants, which seem by many nuanced detail to have had a “rough life”. They look inferior in health to plants I have seen grown at 20 hours of light, with a modest 4 hour reprieve from photon bombardment.

Of course, there are some exceptional (and always improving) autoflowering genetics these days, and the quality and harvest of an autoflower grown seed to harvest under long daylight hours is well evidenced.

From a perspective of, “What’s the best smoke I can harvest” there is great difference between the quality of photoperiod and autoflower genetics, on the whole.

From a perspective of, “What’s the quickest smoke I can harvest” there is little difference between the speed of a photoperiod grown under a flowering cycle, and an autoflower grown under a prolonged light period.

From a perspective of, “What’s the most smoke I can harvest (within a given time frame)” there is a contextual consideration; where in lower light intensities with limited CO2 concentration, one advantage afforded to autoflowers, is that they can slowly accrue a greater total energy store in each 24hour cycle, and thus synthesize greater biomass than comparative photoperiod genetics grown in the same time frame. Under higher light intensity with supplemented CO2, it may be that the approximate DLI of 60+ which is estimated for Cannabis can be reached, and that the twelve hours of darkness may be greatly beneficial to soil ecology and plant hormonal regulation; a higher quality of herb is harvested at still peak quality; whereas a side comparison of an autoflower provided identical light intensity and CO2 may experience diminishing returns on yield, and the plant morphology becomes bulked in growth from stressed metabolic systems, and thus provides a marginally bigger yield at potentially a disproportiately lower quality.

That’s to say that if you’re trying to make your real-life time in X months convert to the highest profitability potential from the greatest investment of inputs, the allure of day-neutral cannabis which can sponge light indefinitely due to its genetic ability to build ethylene and other flowering hormones without a dark rest period may not be as lucrative as originally imagined; it may be rather lower quality weed, and only slightly more in yield than a photoperiod genetic which is limited to its short 12-hour window of photon access; but which you have pushed through environmental control for the reduction of limiting growth factors.

Too there are breeders such as DJ short who recommend starting seed under an 11/13 photoperiod, to coax unusual expressions; particularly toward influence of narrow-leaf drug traits.

One theory these changes in expression are seen from such a marginal shift in light hours (12/12 compared to 11/13) is because of “DLI” or a plant’s photon apetite; belief that the 12th hour represents roughly 8.3% of the seedling’s total light apetite, and so therefore its internodal spacing elongates as it continues to grow approximately 8.3% greater in height each day than its 12-hour filial counterparts.

Another theory uses the logic of the equator at its crux: that the cultivation year in many equatorial climates is clearly delineated by two roughly six-month seasons: a Dry season and a Wet season. It is this 6-month period of time which corresponds to sunlight hours, where there are nearer to 13 hour day lengths in the dry season and nearer to 11 hour day lengths in the wet season. And so the second theory posits that starting seed under 11/13 mimics seed which germinates and emerges in the wet season; adapts to its current season, and anticipates the form it must become to successfully flower in the coming dry season. Conversely, the seed started under 13/11 mimics seed which germinates and emerges in the dry season, adapts itself appropriately, and prepares for flowering in a coming wet season. This miraculous trick is quite simplified in explanation through evolutionary adaptation; for it is logical that all seeds which germinate and emerge under an equatorial 11/13 season and reproduce are the ones which successfully flowered in the 13/11 season. And so, it is thought that our ancestral cannabis genetics from equatorial regions adapt readily to the diametrically opposed seasons they routinely endure, and that this mechanism of adaptation may be leveraged through the simple means of plus or minus an hour with a mechanical timer.

Nature evolves for aeons, waiting for us to hack it. Unfortunately, we most oft exploit it.

-Dr. Zinko


9 weeks veg at 18/6 pop em out June 1. Most commonly used light cycle is 18/6 by MOST growers. Sooth transition is the key for me. During your veg, phase, concentrate on root growth and branching, more than a large plant. Photo’s growth outside dwarfs any efforts indoors, I wouldn’t waste the hydro doing 24 hrs, but I never have. As said above, watch putting out too soon, as light cycle increases until solstice. Safe frost date in our parts is last week of May anyhow. Do your stress/training/topping from the start, but you can top weekly or more all June and July. End up with a bush, not a beanpole. Experiment with funky light scheds after you are competent, go with proven methods, not ‘innovative new BS’ that use the word ‘theory’ when you are starting out. Follow mother nature, not someone name Dr. ZINKO. bet he has a red foam nose in his lab coat. LOL

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If I want to know sex immediately, I start em under 10 hours of light a day, and kick it up to normal >16 hours after a couple weeks.

Otherwise it depends on the internode distances. If they’re too dense I’ll give em a random addition of dark hours. Not enough to put em into flower, just to stretch em a little.

If they’re stretchy I’ll leave em under 24/0 of a bright white / blue light, and their upward growth will damn near stop as they fill in.


I need to sex my small plants, and then put them back into veg so may try this short light cycle.

Don’t have the room for all the plants I started so need to cull a bunch of males!


I just leave the lights on seeds or clones along with my veggies . A week or so before its time to move outdoors I start to harden my plants off by moving out under the sun for a few hours . Then back under the LEDs works for me I always end up with way more than I can use .

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What @gramps said. It’s absolutely crucial to harden your plants before putting them out for good