autoflowering cannabisFast growing autoflowering cannabis plants can use a lot of water but over watering can slow down the growth and can also lead to a number of diseases and fungus infections.

So first of all we need to understand why autoflowers need water?  Well, basically water is the plants fluid of life and it takes up more than 80 % of the plants total weight. When you water the soil water dissolves nutrients and then that nutrient rich solution is absorbed by the roots and transferred upwards to the stem and eventually to those green leafs. This flow of water from the plants roots to leaves is called the transpiration stream because when the water gets to leafs more than 99 % of this water evaporates into the air. The remaining water is used by the plant in the photosynthesis process.

What water to use for autoflowers?

Before watering the plant we need to know what kind of water to use. in all honesty any tap water will do just fine and many growers all around the world use plain tap water and grow beautiful plants. One more solution is to use rainwater, because it is almost pure from salts and other chemicals and cannabis plant will love it. Before watering the plants with tap or any other water you should let it sit for couple of days in open top container. This process will allow the water temperature to reach the temperature of the surrounding air and the autoflower plants like to be watered with water that is not too cold or not too hot because cold water can shock the plants roots and stun the growth for a wile.

When the water sits in the open top container there is another process occuring and that is the dissipation of Chlorine which can harm your plants if it is found in high concentration in your water when you apply it to your plants. This chlorine dissipation happens by releasing bubbles so for the first day or two you will be able to see bubbles form on the container walls and when they are gone this water is ready for usage. After your water has sat for several days in that open top container and is ready to use you also need to check it’s PH level!
The PH of the water you give your autoflowers should be around 6.5 to 7.0 but a little variance to each side won’t damage them that much.

When to water ?

This probably is the most asked question by new growers but the truth is that there isn’t one schedule or one amount of water that will fit any cannabis grow operation. There are too many variables to the equation – some of them are: size of the pot, soil composition, air temperature, air humidity, air circulation, plant size, plants age and so on. After this long list you can see that there is just too many of these factors and you can’t introduce one formula for every grower but a general watering guide can be established!

Watering before germination

Before putting your precious autoflowering cannabis seeds in the growing medium you need to completely saturate the soil from top to bottom. What you need to do is pour two or three times the amount what the pot can hold and let it run off the bottom. This pre-planting flushing process is needed for the whole soil to get completely wet. If there are some dry soil pockets then your plants roots wont grow there and those dry spots can also be good places where high nutrient concentrations can appear when they eventually get wet!  When all the excess amount of water is drained away you still need couple of hours to let the soil dry up a little. This drying process means that the time before you can put your seeds in the pot, after completely saturating the growing medium, is somewhere from 3 to 5 hours depending on the surrounding temperature and how fast the water drains and evaporates.

Watering at the germination stageSolo418 handheld humidifier 

In the germination phase of the plants life you should be very careful with watering because that autoflower seedling is very fragile and it will easily bend if you water the soil surface too hard. When that little sprout is in this stage of growth it is better to keep the surface moist but not too wet and it is better to use a hand sprayer to moisture the growing medium.  When you are watering this little herb don’t pour/spray water directly on the stem of the plant but around it because it can easily get a stem rot or fungus / mold.  Basically you need to keep the surface of the soil wet and that is it for this stage of growth.

Watering after germination

After the seedling has established itself and the first couple of true leaves have showed you need to let the surface of the soil  dry up before the next watering. When you see that the surface of the soil (2 to 4 centimeters, 1 to 2 inches) deep is dry then you can water it again till a little runoff water starts showing at the bottom of the pot. You can also use soil humidity meters for a more accurate reading but it is not necessary for beginner growers. 


Over-watering is almost impossible to do in just one watering, it occurs when you water your plant too often and don’t let the plant use all the water before watering again. It is better to let the plant experience a little dry period than over watering it. If you over-water your autoflower plant the roots will not be able to get any oxygen so the plant will suffer and will start turning yellow. Over watering the plant also introduces the risk of fungus and root rot and those are some serious issues better avoided by just not watering your plants that often.

Over watering can be fixed by just letting the plant soak up all the water for a couple of days and dont give it additional water till the growing medium is completely dry again.


Under-watering isn’t as big of an issue because the plant can survive long periods of drought and the soil is kept well irrigated and full with nutrients when you underwater rather than over-water.
When your plant doesn’t receive enough water it will start to wilt, because the plant cells that  kept stems and leaves rigid by the water pressure in the cells won’t be able to get enough water and start shrinking and your autoflower plant will start to wilt.

This process can be reversed simply getting water to your plant as soon as possible and in a couple of hours those leafs will be up and they will look as new.

Rapitest Moisture meter

Best Watering methods (watering guide):

1) Watering when the soil surface is dry by pouring water till there is a little runoff water at the bottom of the pot. This method needs you to touch the growing medium and can get a little messy so avoid this if you need to do anything else in your garden.

2) Watering by the weight of the pot. This method is one of the easiest and most commonly used methods. After watering the pot feels heavy, but when the plant has used all the moisture your pot becomes light and you can water it again.You just need to lift the autoflower plant up every day and judge the weight of the pot. At first it will be a little hard to know when to water but practice makes perfect and soon you will be able to tell when your plant needs water just by tipping the pot sideways.

3) The third and the most controlled method is to get a soil moisture meter that shows exactly how moist the soil is and you know exactly when to water the plant!

There is also a method that you can water your plants by pouring water directly in the planter tray and let the growing medium and roots collect the water by sucking it up from the tray. This method is great for tall pots as it makes your plant roots to strive for water and grow deeper so you can get much better root mass.



  1. Mr.Magoo on

    What’s the best method for outdoor pants? Normally I water when the to soil feels dry but I’m herring the wilting and yellow leaves 🙁

    • midowo

      You could make a spherical bed around your autoflower and pour water there so it will stay wet longer, but usually outdoors cannabis don’t need so much watering!

  2. semperfly on

    I’m going to use a bathroom body weight scale. I will weight it when its dry and fully watered.

    • midowo

      You don’t have to bee so strict but it you are a first time grower you can do it at first.

  3. midowo

    I suggest to start using nutes at the second or third week and start of slowly by giving 1/8 or 1/4 of the required dose.

  4. carbonunit dave on

    Cannabis plant roots doesn’t like to be wet for very long and full grown autos will drink a litre a day so adding perlite is great for drainage and vermiculite will retain water until it’s needed e.g. if you miss a watering.

    • midowo

      Autoflowers are no different than regular photo-sensitive weed when it comes to hydroponics. I have not grown in Deep Water Culture myself but have seen many growers getting amazing yields.

    • FightingDirty on

      Autoflowers in DWC using a wilma Xl and 25l pots, get 100g+ per, water 18 hours a day after 3-4 weeks in and roots are showing through bottom of pots. DWC ARE AWESOME! BigDevil Xl seeds, says 9.5 weeks, mine take 11 weeks usually.

  5. Jackyork on

    I’m on my 4 th auto grow and always looking for tips and tricks to max the yield, I end up going from forum to forum looking for my exact query, It’s time consuming and don’t start me on registering every-time.


    Well done and thank you.

    • midowo

      Hi Jackyork,
      Tnx for those kind words!
      What strains did you grow for those first 4 grows?

  6. Jackyork on

    Hi Midowo, My mistake it’s my third ‘Auto’ grow and I’ve also done two normal grows. I have tried a mix bag of Auto’s that inc Bio-Diesel, Ak Auto, Berry Ryder, Royal Cheese. At present I have 1Jack Herra 4x candy cush (may have got that name wrong but very similar lol) 2x Autopounders and 1x Royal Dwarf. I am averaging approx 40g dry per plant but would love to get it up too 2oz in time.

    The biggest issue at present is Germinating.

    I germinate using ‘Jiffy elitists’ up until this grow I have had a 100% success rate but for some reason I’m having major problems germinating the seeds even though I’m doing exactly same method.The weather has turned colder and my method after I’ve put pellet in water I put seed in approx 1/2 inch , cover gently with soil and put pellets in propagate dome put next to boiler in Airing cupboard, normally after 2/3 days It’s approx 2inch long, for some reason now nothing is happening I have tried different seeds thinking it could be a dodgy batch but still nothing happening …..Any Ideas why or methods I could change too. Thanks in advance. Jack.

    • midowo

      Hi Jack, I see you have grown some great strains before and 40 g is not bad!
      As for the germination, I really have no idea what could be the problem, you have to think what else has changed from those previous germination conditions, maybe the water supply is different, or that average temperature is a bit too low as you mentioned – the weather has changed.
      If you manage to find what was the problem , please shear it here, as I imagine other growers could have the same problem.

      • hi im growing some white widow auto’s i have them under a 250 hps and a 18w flouro/ white! do you think that is sufficiant for 4 plants? have you grown white widow auto’s and how did they turn out?

  7. its only a cupboard grow so not got a intake or outtake, have a oscilating fan but thats all! can i still get a good yield from these w w auto’s?

    • midowo

      Hi Stuart,
      I think 250W HPS + 18W flurorescent will be enaugh for your first grow but if you really want to maximize the grwth I would suggest to add more CFL bulbs.
      How is your heat in that room? HPS gives off a lot of heat and without intake and outtake fans it can become quite hot in that enviroment.
      I have not grown WW autos myself but have heard good things about them!

  8. Hi Midowo,
    I am using the Rapitest Moisture Meter. What is the best moisture meter number for cannabis plants (autoflower)? Thanks!

  9. I’d like to get that rapidtest meter because I have a problem with over watering. What should the reading be for cannabis when dry? apparently there are differing ideal readings depending on the plan in question, and I doubt they have cannabis on their list lol Thanks

  10. Hi midowo I’m growing 4 auto northern lights in a space bucket I made out of a water butt it’s been 2 weeks so far n that got there second set of true leafs n going well I water them every two days n that looking nice that about 1/1hlf inches tall

  11. Oerganix on

    @MIDOWO What is the point on the Rapidtest meter where it would be time to water the autos?

    • midowo

      Hi, it depends on the soil that you have but the best option is to wait until the meter reading goes down to the range of (1-3) where usually the “2” reding is the best choice. It’s ashame that the company does not provide a watering guide for Cannabis plants.

  12. The top of my leaves seem to be dry and curling up a little. I have a hard time keeping the temp below 90 so I figured that was the issue. Should I mist?

    • midowo

      If your plants are still in the vegetative / early flowering phase then you can myst them. But the best option would be to somehow try to reduce the heat.

  13. D3V!ous_Dankster on

    My short rider autos from nirvana are almost a week out of soil,as of now they have been under 24 hours of 96w t5ho light from birth. They are in 3 gallon pots(from seed). My question is,when can I stick my 300w LED above them and how far above……..thanks.

    • midowo

      I would wait a couple of days and then put that CFL as close as I can without burning the plant tips.

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