Autoflower grow guide: everything you need to know about autos


autoflower grow guideAutoflowering cannabis plants are pretty much the new kid on the block, only really making an appearance on the mj growing scene in the past few years. I’m aware that some of you may never have tried growing autoflowering marijuana, and thought it may be worthwhile sharing my experiences with them. This is not written as a “autoflowering grow guide” per se, but a collection of thoughts and tips that hopefully will encourage some of you to give these a try. 

There is a developing niche user-group for autos. There are excellent forums devoted just to their use (see and any posts by the knowledgeable Muddy) and some great seed-banks who are building extra reputation by expanding their ranges of autoflowering seeds for sale. Personally I’ve been playing with autos now for nearly 7 years. I’ve grown approximately 100 different strains both indoors and out. This is partly the result of never being able to say “no” to the thought “its only 7€ I’ll just pop that one in amongst the tomatoes” and lately because I am in the process of developing 3 different strains myself (and that’s another article altogether).



And yet, despite having now grown so many of these from seed, I still have very mixed feelings about autoflowers. Certainly the journey thus far has not been a smooth one and at times its felt like I’m banging my head against a brick wall. Almost all autoflowering seeds are described as being between 7 and 10 weeks seed to harvest, and their finished heights supposedly 30cm to 1m. I’ve experienced yields ranging from 5 grams a plant (“lowbolt” from sagramantha seeds, at 13cm) to one “cream caramel” (sweet seeds) which gave an astounding 105g after an equally astounding 126 days (that’s 18 weeks not 8!). With such a mixed range of development time, yield and growth its not surprising that when it comes to autoflowers, growing can be a difficult experience. Hence the reason for this autoflowering grow guide.


As we all know, cannabis is a photo-period plant: ie it’s flowering hormones are triggered by changes in the light/dark cycle. Thus you can stimulate a 2 week old cutting to begin flowering by giving it 12 hours of darkness, yet a 4 month old plant grown outside will remain in vegetative growth until mid-summer has passed.

Autoflowers are a different breed altogether (quite literally!) and will flower according to the age of the plant rather than the light/dark cycle. This development has been obtained by crossing a ruderelis strain with a standard photo period plant. Unfortunately ruderelis is fairly weak in the desired thc levels so the first autoflower strain developers had to stabilise two dominant traits: the high thc level provided by the photo-period parent and the all important auto gene from the ruderelis strain. As you can expect, early attempts were generally disappointing, and as little as four years ago autos were viewed as unreliable with poor yields and low thc levels. Most sensible growers put them down as gimmicks for newbies.

Today if you see an autoflower seed for sale you can be (reasonably) assured that its THC content will be as advertised, and its auto gene stabilised.



Now this is the big question. Most breeders claim 7-9 weeks, with some even boasting seed to harvest in less. It would be fantastic if one could get 50g per plant after just 39 days, but lets face it, its totally unrealistic. A plant doesn’t grow any faster for having an auto gene, and the dwarf autos that will harvest in ultra quick times are just that: dwarfs and thus yield is limited by size.

Of the 15 or so different commercial strains I have tried, not one of any consequence finished in less than eleven weeks – and the best ones can take anything between 3 and 5 months. If you think about it, this is not surprising: most standard autos start showing their sex at around 21 -28 days (super autos not included) – if you add on a flowering time of 8 weeks (average flowering time for a indica) then you would be looking at 11 – 12 weeks. 

Read about growing autoflowers >>

47 thoughts on “Everything you need to know about autoflowers: a grow guide

  1. Cm says:

    Most amazing site for all information needed, within a matter of minutes i have knowledge that would have taken me hours to google! Awesome site with the live chat will be comming back lots for questions!

  2. terry says:

    Could you convert your Godless measurements to standard one’s? metric is of the Devil thank you p.s.super great info.really helpful!

  3. terry 208 says:

    I have to throw out my 6 wk. old auto bubblelicous plant that is covered in flowers and bud sites because it ‘s 5ft/3in.tall and growing (6 1/2ft from bottom of pot to top of plant) I have 2 in. of space left i’m very sad and disappointed.this was my first grow maybe my thumb is too should be 2ft.tall max.

  4. terry208 says:

    I cut 6 in. off the top of my 10 week old auto bubblelicious plant 3wks. ago due to ht. 6ft/10in. the cut site stopped growing but the 3 nearest branches zoomed past the cut spot and now are three 6in. bud clusters the plant is loaded with bud clusters even at the bottom the bud and surgar leaves are healthy and look great but 80% of my fan leaves have turned yellow and died or are dying my bud pistils are about 55% red should I be concerned about my fan leaves thank you p.s. first time grower

  5. campo cultivator says:

    Hi Terry
    Well many people don’t advise pruning autoflowers although I main stem tip prune mine (which is what you have done) normally around week 2-3 as I find it encourages branching and better buds.

    Re the fan leaves yellowing: these will yellow as plant matures BUT if 80% of your leaves are going yellow it suggests there is a problem, most likely reasons are:
    Lack of nutrients due to a PH imbalance
    Possibly even light bleaching (although leaves tend to look pale rather than yellow)

    Have a look at these and if there are still problems, let me know


    PS love your comment about the pet chicken, I often feel the same myself, I had some super stinkys that were with me for nearly 6 months, I had thought about naming them and writing out the adoption papers .. the only answer is to have your next baby ready to go so you’re impatient to make the space for her :)

    • terry208 says:

      Hey Campo, thanks 4 the great info. my soil ph is 6.7 and the leaf loss is now at 95% at the same time i’m growing new leaves and flowers at the bottom of the plant perhaps because I have a 2nd light hanging over my 2 week old plant that is providing it with extra light at the bottom also I look at my buds with a lighted jewelers glass and they are dripping with what looks like crushed diamonds and course sugar I think I will harvest in about a week thanks again.

  6. Chuck says:

    I planted my seeds straight in the soil and did not germinate it’s been 4-5 days and no sprouts yet, did I screw up. Should I germinate and start over, I used auto flowering seeds.

    • weed widow says:

      i keep mine under the light whilst flushing – but i know some growers give a final day of darkness before cutting

    • campo cultivator says:

      Hey Graham
      lol a bit of a tardy response apologies
      Generally I like to flush for around ten days if possible until I see the plant start to eat itself meaning its taken colour from the leaves cannibalizing itself as such

  7. clive says:

    Ive planted 4 autoflowering seeds in 4 pots in 1 pot ive 3 growing in another 2 growing and 2 bad boys anyone no wats going on this is my 3rd time growing never seen it before or heard of it any help im 5 weeks in but looking good

    • weed widow says:

      hi there – well the ones i’ve tended to use (and liked) are General Hydro Flora series and Canna (but you really DO need the Canna Boost) – we have customers who swear by House & Garden as well

  8. Zac says:

    You mention “super autos aside” in reference to the auto flowering plants taking 21-28days to show their sex. how many days do the super autos take to show there sex and what are your favorite strains of super autos?

  9. weed widow says:

    Hey Zac – when this was written a few years ago, the superautos were a new breed of autoflowering cannabis, & there were only a few of these super strains around. Chaze was one of my favorites (Short Stuff seeds). They took / take anything up to 2-3 months before showing sex (the Super Stinky especially took 5 months nearly to go seed to harvest! but gave a whopping 300g per plant).

    Since then there were are a lot of “semi” super autos around. This year we grew Dinafems new XXL Auto range – these are 12 weeks and were a good 3-4 foot tall, sexing around 1 month. Can’t say end result as unfortunately the local police confiscated them but I have to say they looked outstanding up until week 4 (when they were taken)

  10. craig says:

    Hi im a first time grower and have just purchased auto flowering seeds can you tell me if i just put the seed straight into pot in my set up and give 1mm of feed? Thanks

  11. richard says:

    Hi im on my first grow with autoflowering plants they are 6 weeks old and have been under light 24/7 would they benifit under 20/4 lighting cheers in avance

  12. Auto says:

    auto white widow from pyramid seeds
    Shown first pistil at day 28 and growing healthy and big but no real bloom or flowering almost day 70 reaching but looks like day 70 healthy plant many branches and one thick stalk plz help

  13. sinned214 says:

    hello,i’am a first time grower i have loved plants all my life (born with a green thumb) your info is an inspiration. my tail is waggin. i think i love you. i will write back in ten weeks with news about my auto blue amnesia. she came to life on 1-19-2015, proud dad its a girl. POWER TO THE PEOPLE

    • weed widow says:

      Hey cheers for such a nice comment! Send us pics of your girl when she’s done ([email protected]) and we’ll post them on the site. I’m a big fan of amo strains but have never tried the blue amnesia … Seems to me you’re going to enjoy growing as much as I do!

  14. kismet says:

    Can you grown cannabis plants like an ordinary plant without all the lighting, feeding, etc?

    I understand there won’t be a massive yield, but is it worth trying to grow a cannabis plant indoors in a pot, just water it every couple of days and do nothing else, then when it’s grown enough, harvest it, cure it, then smoke it!?!?

    • Becky says:

      Did you try? As long as they get sunlight they will grow in a window sill until strong and big enough to go outside – just make sure to repot into bigger containers before they get root bound… 1st year of doing autos so am looking for more knowledge.

  15. smoky77 says:

    hi guys newbe here on my first auto grow think it’s going ok but iv started to get new leaves grow from my first true leaves after other growth elsewhere is this normal and is it a good sign? many thanks guys

  16. sasha says:

    Hey guys, i’m on my second grow now, and my first auto batch, I got some fast & vast auto (heavyweight seeds) from jungle seeds, originally they were gonna be grown out doors but my partner was a bit too excitable and decided to take the lead with it unfortunately the winter has set in now so I’ve had to move what I can inside, so I’ve got 7 left out of 27, really not happy about this but I guess that’s people sometimes haha, but yeah so they are around 9 weeks old now and have had a bit of a a slow start with the weather conditions but they’ve been in my cupboard for about 2 and a half weeks now, it’s amazing how fast they grow, when I put them inside they were only about 2 or 3 inches tall topos but now they’re getting on for a foot high now, i’m so excited :)

  17. mike says:

    I need some help. I can’t get my autos to finish I use plenty of light feed them right. Temp is good but still cola doesn’t for tight. I have grown 7 foot plants inside hydro. Could you maybe tell what I’m doing wrong.

  18. Ww says:

    Autos are amazing, all the issues you describe I have not seen come to fruition. I am averaging close to a pound per plant dry weight. And the seed to harvest times are almost spot on.

  19. Robin Ferri says:

    They say even if you have a black thumb you can grow these…so I am going to try…planted an auto big bang in it’s home pot…a 5 gallon pail under a 500 watt LED…used pro-mix medium…..under gentle spray of water, she sprouted up in 5 days…heading to week 2….first set of leaves are large and showed themselves just a day after sprouting…I’ll see how it goes…

    • weed widow says:

      Good luck with it Robin! Autos are by nature vigorous and want to grow. Keep your LED up high during veg and encourage her to stretch up to the light.

      BTW One of our growers did the Big Bang Auto last year and its been a big hit at our Smokers Association! Good choice :)

  20. Robin Ferri says:

    I was wondering if they are auto feminized, do you need to cut the light schedule any way…I am on 24/0 @ two weeks on the 18th..working on the 3rd set..if I need to cut the light cycle please can you tell me when I should…1st timer! I was under the assumption that the length of light cycle didn’t matter with autos..I am growing the strain auto flowering feminized big bang seeds…

    • weed widow says:

      Hey again! No, the great thing about autos is that they aren’t fussy about light schedules, or interruptions in their light cycle. Here in Spain, they are also known as “automatics” ie they automatically start flowering at a given stage in their life. So darkness hours are irrelevant to triggering flowering.

      You can keep them on 24/0, or alternatively change to 18/6 (or periods in between). I say this because I think 18 hours provides enough light for good phototsynthesis and bud production and I think plants benefit from a short daily rest period. Also it cuts your electric consumption by 1/4. We’ve done both, but I’m not sure there’s any noticeable difference either way!

  21. Robin Ferri says:

    Thank You so much for that information, now maybe you can answer this one…I’m @ week 3 on Saturday from seed….just showing signs of 3rd leaf set…I use a 500 watt full spectrum LED light on 1 plant…what can/ should I be able to yield on that one plant, that’s receiving all the light, indoor environment, Big Bang auto feminized flowering seed variety…any advice would be appreciated.
    Thank You,

  22. Robin Ferri says:

    I would also appreciate your help in choosing a variety of seed that’s auto, fast growing, high THC content and high yield…for medical purposes…
    Thank You,

  23. DckoryB says:

    Hey Campo, Im 32 days into my first grow with 2 auto Candy Canes under a 300w LED in 5 galllon cloth pots. For the first couple weeks i kept the light just a few inches from them after misunderstanding info on distance in flowering/veg. Each are quite different as far as leaves and growth which im assuming is due to pheno with one stretchy and long thin leaves and the other very tight between nodes and fat leaves. sativa/Indica? I’ve LST’d them and both doing amazing with tons of bud sites despite being VERY short, which is where my problem comes in. The one im guessing is the indica dom is so tight with so many buds that the fan leaves on each were covering each other and after trying to tie them out of the way ive pruned a ton (20-30) leaves from the buds.. Do you think this was a bad move? sorry for the wordy post and any advice would be much appreciated from such an experienced auto grower!!

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