Watering Marijuana Grown In Soil

Cannabis plants use a lot of water, and regardless of what sort of setup you’re using, you’re going to want to make sure you have plenty of H2O. There are no hard and fast rules when it comes to watering a cannabis plant since the requirements of the plant are determined by the environment it’s growing in. If the environment is very hot, the plant will use more water. If the plant is receiving the maximum nutrients, it can absorb.

Water acts a vehicle for dissolved nutrients and minerals, being absorbed through the roots before spreading through the rest of the plant. It also cools a plant down, fills up cells to keep the plant structurally sound, and is required for photosynthesis.

In general, water enough so that your soil is faintly moist, but not wet. If the soil is too wet, you risk fungal growth and root damage. In this article we’ll talk about the different ways water affects cannabis growth, covering the following topics:

Water Sources

water sources cannabis soil

The vast majority of growers water their plants from the tap. In fact, you might even have trouble finding reverse osmosis systems in a lot of hydroponics and gardening supply shops, depending on where you live. Some places are blessed with pure tap water. Most places in Europe and North America, however, are likely to have some impurities in their tap water, especially in large cities. While the severity of these impurities can vary, many growers crave precision in their operations, and tap water can carry with it unknown variables.

Most tap water will contain extra minerals. The type of minerals depends on your location. Calcium, sodium, and magnesium are common. The harder your water is, the more minerals it will contain, and there is a huge variety of potential minerals your water could contain.

Download my free marijuana grow guide for a marijuana watering schedule.

When it comes out of the tap, your water could have an EC that ranges from 0.2 to 0.8, or even higher. The real issue here is that even when you take an accurate measurement, there is no way for you to know what sort of elements are in your water, and the ratio at which they occur. This means that all the extra money you’ve spent on expensive, carefully measured nutrients is for naught: the mix is instantly unbalanced by an unknown quantity of other nutrients. In a worst case scenario, this can cause nutrient burns or lock-outs and inhibit the growth of your plants. More info about your water in the articel “Hard or soft water for marijuana plants

How Much Water

How much water weed soil

The amount of water you should use varies depending on the environment of the plant. It depends on the size of the plant, the temperature, the composition of your soil or substrate, the properties of the water you’re using, and the capacity of your air filtration systems. When your plants mature, the environment gets warmer and less moist, and the plants will greater air flow and additional water. Large leaves widen the surface area on which evaporation can occur. The metabolic process is activated by heat and transpired moisture is blown away, which causes the plant to transpire more. Check this Marijuana watering and feeding schedule for more info

When To Water

When to water cannabis on soil

You need to keep soil moist from the very beginning of the life-cycle of the plant – before your seed has even germinated into a seedling. Since the seeds don’t have any roots, they will die if they dry out. At the same time, they drown in too much water. Usually, it’s advisable to keep seedlings and young sprouts hydrated by spraying or misting them with water, to help ensure you don’t drown them by watering them too heavily. Once the seedlings have rooted down, you can start to water them in earnest with a watering can.

As the seedlings root down and develop, you can also let the soil dry out for brief periods of time. These short dry periods will help limit the risks of your soil developing any mold or fungal growth, which can sicken and destroy a seedling. Just remember to water the plant regularly, but don’t let the soil get too wet. Also, make sure the soil doesn’t get too dry, or your plant won’t undergo photosynthesis. Obviously, this will cause your plant to stop growing and die.

Although many pots will come with little trays that retain the water you’ve already used for irrigation, you’re better off throwing that water out and using fresh water. Letting water sit for long periods of time is just begging for the accumulation of bacteria.

If you water the plant with too much volume at one time or water the plant too quickly, tiny channels will form in the soil. Water drains quickly out of these channels, and it won’t be absorbed by the roots. Always water your plants slowly and evenly to ensure good hydration and distribution of nutrients. Also, make sure you are using room temperature water of ~20 degrees Celsius, otherwise the roots could experience thermic shock.

The morning is the best time for you to water your plants. That way your plant has a whole day of sunlight and chemical processes it can use the water for. Watering in the evening increases the chances that you will have to deal with fungus or mold.

Common Watering Issues With Soil

Common watering issues soil cannabis

The number one issue around hydrating plants is over-watering. Don’t do it. Make sure your substrate isn’t constantly soaking wet. If your soil is always wet, there are a whole host of issues that can arise. The roots can rot, the leaves can die and fall off, and that isn’t even mentioning the huge risk of fungal growth and mold. If you’ve been overwatering, stop ASAP and give the plant only tiny bits of water until the roots are white and healthy again.

Also, try not to let your soil dry out too much. If a plant doesn’t get enough hydration, the plant won’t develop properly. Eventually, the cells will lose too much water and the plant will wilt and collapse. At that point, it’s very difficult for a plant to bounce back and recover.


Soil nutrients for weed

In soil, try to minimize your liquid fertilizer application to necessities. For example, if you have a bad soil mix or your growing container is too small, or the plant seems like it’s underdeveloped. Liquid fertilizers can be added to your water source before you water the plant.

Liquid fertilizers are absorbed extremely quickly by the root system of a plant. The thing is, this isn’t always a good thing. Being absorbed so quickly means it’s very easy for you to add too much fertilizer, which can damage the plant. This double-edged advantage/risk is the reason you want to tread carefully when it comes to liquid fertilizers.

You’ll also be able to choose between chemical and biological liquid fertilizers for your plants.  The biological liquid fertilizers usually work the best, and you don’t have to worry as much about toxicity or any long term damage to your soil or water. Unfortunately, most of these are algae-based and they have a tendency to be kind of stinky.

You also have the option to fertilize the plant and provide nutrients through the stoma on the foliage. The pores on the foliage absorb nutrients quickly as well. Just spray a highly diluted nutrient solution on the leaves and then rinse the leaves off afterward with normal water.

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible


Avatar for Robert Bergman

Mr Robert Bergman PhD


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

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58 comments on “Watering Marijuana Grown In Soil”

  1. Hi Floyd,

    Thanks for your comment. It depends on the exact product. But we find that their products with slow release fertilizers don’t work very well with Cannabis, and they tend to contain a little too high concentrations of nitrogen, which can pose issues in the flowering stage. Its just not the ideal product to use for Cannabis cultivation and there are some awesome brands out there, that tend to give much better results. I hope this helps, but let us know if you have further questions!
    Happy growing,

  2. about miracle grow I lost my first grow of 16 plants to there plant fertilizer.plants where about 5 feet tall looked great between the fertilizer and extream heat they just curled up and died pete k

  3. Mark, It appears that you are just trying to add too much ro too many ingredients. I am glad to see you figured it out.

    FF, Thanks for the tips. 🙂

  4. LK,

    I agree, it appears to be nothing more than leaves that are done converting sugars and die off. This is natural. 🙂

  5. To get back on topic a bit more – if you want to be an absolute purist I suggest storing rain water in five gallon GLASS CARBOYS that are available from Home Brewing shops and stores. Failing that, the other option is five gallon plastic jugs made of POLYCARBONATE (a very strong plastic that does not leach any of its substance into whatever is kept in it). The symbol for polycarbonate is a number 7 (seven) inside a triangle – this should be molded into the bottom of the jug somewhere, and if you see some other number in a triangle shaped mark don’t buy it. You want polycarbonate specifically not some other plastic.

    The simplest way to collect rainwater in fact, is to stand the jug or carboy outdoors with a large funnel in the top. You can collect water that runs off of a roof – but what else may have been on the roof? What are the shingles themselves made out of? Better by far to just stand the jug out on the lawn in the backyard or wherever and let it fill up directly


  6. Buy a meter that measures ph levels. Even well water can be out of the ph level you need. 5.5 ph is the ideal. Use ph up or down to get to that level.

  7. I had a problem develop when I transplanted a Sour Diesel plant into a 20 litre Rocket Pot. I made up a mix of CannaTerra Professional and Mushroom Compost. The mix was around 50/50. It was around 2 weeks before the plant was showing signs that it was not liking the soil and watering. Some of its leaves were starting to yellow and also curl down and droop slightly. At first I thought it was a nutrient deficiency and gave it some Nitromax 17 but this only compounded the problem as it was not needed. I transplanted it again into just a pot with CannaTerra and it has started to rehabilitate, i think I just got it in time. Gardening experts say that Mushroom compost feeds the soil and not the plant and helps with water retention. I found that when I transplanted the plant the second time that the water had only penetrated the depth of the soil that the roots had gone down to, around 10cm and the rest of the soil 20cm depth was absolutely bone dry. I have also been giving the plant RYZO and that has been helping as it is good for reviving sick plants if they are not to far gone. It has started showing nice green leaves now and is 55cm in height. I also have it outside now. One final thing I grew an Hawaiian Skunk plant outside during our winter and it reached 64cm in height and I harvested 65grams off it in total. We have a slightly Mediterranean climate but winter averages around 15deg Celsius and daylight around 10 hours. The spot I had it in did not get the sun for the whole day, but it was in the soil so I could not move it. The plant is a very good smoke so I was quite happy.

  8. Thanks for the well watering tips. I am starting my girls with well water after sprouting the seedlings with distilled water and nutrient. I’m noticing that mixing my well water with distilled water 2W/1D I’m getting about 128ppm. This should work. I will transplant from Aerogarden to soil this week and see how it all works out.

  9. Please explain why we have pale yellow leaves, large & small, singularly, in random areas, on our plants. They have been in flower approx. 2 weeks,
    are about 40″ tall, in fabric bags in plain Triple Mix soil, outdoors. Good color & turgidity over all… just puzzled. Most yellow leaves are 2-3″, a few large fans. I leave them on until they are very pale or obviously drying/curling. Have no signs of pests EVER, we monitor closely). Used Miracle Grow 15-30-15 a few times,
    now just dilute Aquanure (trout effluents, veg & root compost, hardwood ash,
    molasses) from Croxall Farms/Canada, as per instructions…. About weekly,
    w/ very pure well water. I don’t feel this is a watering or nutrient problem,
    perhaps simply ‘end of life’ for these random leaves? Thanks for all you do
    to help us out here!!

  10. It would be great to have pictures of what plants look like when over watered and under-watered.

  11. The first thing I would do with your well water source is check its Ph level with a simple PH Kit you can find at any garden market or amazon. Outside of any obvious contaminants, High or Low Ph levels of water can be limiting your plant root’s intake of nutrients. Ideally, You would want to test your soil AND your water source for proper Ph levels in between 6.0 and 6.5.

  12. whats your opinion on using superthrive in flowering or just the product itself

  13. would like to get the info lol. cant get right should be my name. need help for hydro ,germination, nutrients etc. have it all just doing something wrong

  14. My last grow with miracle grow. got a gift for xmas was a aero garden hydro unnit Anyways i had 10 bag seeds to see if the would sprout. sure as hell they did and they are all female.Areo garden is small and the weed grew fast(i started early im new)
    anyhow they are very well stalks are big so i think im ok

  15. Mike,

    There are many factors that go into keeping the terpenes from leaving. Go here for more discussion: ter·pene levels. support.ilovegrowingmarijuana.com

    From dictionary: ˈtərpēn/
    plural noun: terpenes

    Any ny of a large group of volatile unsaturated hydrocarbons found in the essential oils of plants, especially conifers and citrus trees. They are based on a cyclic molecule having the formula C10H16.

    late 19th century: from German Terpentin ‘turpentine’ + -ene.

  16. Miracle Grow is now owned by Monsanto, and if you did not have a reason to not use it before; You certainly should now!

    Also; Organic soil is not at all time released.

    Most experts want to know what they are feeding there plants and therein lies the reason for more control by building soils at home.

    Happy growing 🙂

  17. scott,

    I say no but, many growers are going against proven grow methods. It is a personal choice.

    Go here for more detailed advice: support.ilovegrowingmarijuana.com

  18. Robert I couldn’t agree more, If one person could substantiate their claim against miracle grow I may understand why they feel that way. Ive been growing for years now and although there certainly better soil mixes out there I prefer to use, I have grown a half dozen successful crops in miracle grow.time release has nothing to do with it,, compost which everyone agrees is a good soil additive,it’s main function is time release of nutrients and micronutrients in fact half if not most organic compost mixtures on the market will do way more damage than miracle grow, you really just need to understand how much time you want to spend getting to know how each growth stage of the plant requires different concentration levels and know that when my miracle grow is new it’s full of nutes and it will shock a plant If it’s not properly calculated . But unless people stop believing everything they read in alot of forums out like this one they’ll never be able to make an informed decision.Cause everybody has their own way to get the job done. I suggest everybody needs to fail to succeed and you can follow any grow Bible and it will inevitably conflict with the next guys grow bible, do a lot of research and stay away from sites that sell a product of any kind, they will always be biased towards the competition, like miracle grow,that rumor was started years ago and probably by some tofu eating boulderite that’s wanting to be the grow guru for the masses instead of being helpful, but somebody post some real hard facts about what it is that makes it so bad and I’ll listen but it won’t stop me from using the product unless it contains something more toxic than any other product in the nurserys today,

  19. This was my first grow, six auto flower seeds, all grew great harvested in 11 weeks, but no skunky smell, did I do something wrong?

  20. started grow of white widow, into start of week 6. Leafs are really big compared to other grows, should I start removing large ones so light gets down lower parts of plants and fimming

  21. Wish I could show a pick of what miracle grow can do. There are so many misconceptions on how to grow a great plant. Don’t listen to them brother treat your plant just like it was a tomato plant and you will be fine !!!!

  22. Can you tell me what is behind a seed that grows two plants from the single seed. Is there anything i should do other than let it grow ?

  23. TSB,

    No pictures here. Join our forum and we can help you. We have a very friendly community, and willing to help you grow successfully from start to finish.

    Happy growing,

  24. Hey what do you think of these, from seed planted in the ground in june. Straight rainwater and miracle grow. What do you think about when to harvest. I think a couple more weeks min.

  25. Steven never use Miracle Grow. It has time released nutes that is not good for cannabis. Although bag seeds are very unpredictable. Good luck

  26. I’m currently waiting for something and I found out I may have to wait a month. Highly unlikely but still. I found some seeds in some dried out nasty tasting dirt weed. It gets you high, if you can handle the taste. Anyway, I got some seed starting soil from miracle-gro and found 13 seeds in it . I bought the little pots, poured the soil. Took a pencil and poked the dirt about 3/4 of an inch deep then dropped one seed each in 13 different containers. I then slowly moistened and watered them all. Don’t pack the dirt, let the water do its job. I used warm water and kept the area warm also. Eleven of these babys popped up and I am really going to need help because this is my first. I don’t know what I have. I have a 500 watt ggrow lamp and a 2’x4’x5′ tent. 2ft wide,4 ft long and 5 ft high. I bought moisture control miracle gro soil for when I transplant and I’m going to use 5 gallon buckets, but maybe fill with 3 and a half gallons to 4 gallons of dirt. I’m hoping I can grow 5 if their are that many females. Its been 7 days and I still have eleven. If someone can keep up with this with me it would be awesome. Thanks, for now

  27. I also live in mass. I use R/O water and distilled water. I would love to talk to you about tips on how to grow as I am on my very first plant.


  29. second year growing….last year I germed 7 seeds, only 2 survived to the end. Some rookie mistakes were made like heavy concentrates of fertilizers, too much water, used soil from 1 of my wife’s planters…etc. After downloading the Grow bible and researching blogs and forums all winter, I feel scholarly. Proud to say I ordered strains conducive to outdoor grows. My plants are in their 6th veg week using mushroom compost, and worm castings along with some Epsoma Organic Grow in the water. They are 4ft tall and have been fimmed, and super-cropped doing beautiful. Can’t wait until flowering. By the way I haven’t smoked since 1989.. just fascinated by how complex weed really is…sativa’s, indica’s, hybrid strains, how to sex em, how to make a plant produce seed that is female……..mind boggling

  30. Phil,

    It sounds like your humidity RH % is through the roof. High humidity in the air will help to keep your soil from drying out. You should be holding RH at 50-60% in Veg and 40% (optimum) in bloom.

    Perhaps you should join our support forum in order to share information and obtain a more informed answer. See you there 🙂

    lw – I❤️GM

  31. Thomas,

    Wel water can be great for your plants but, can contain metals that could cause an imbalance in your nutrient solution when mixed. I suggest that you get your water tested at your local aAg University or county facility. It is a good thing to know what is in your water and your plants will thank you for it.

    Happy growing – I❤️GM

  32. robert green,

    It is hard to say how long you can store water in an open bucket. It could be influenced by what type of bucket and the material it is made of. Also; debris and other air borne contaminants can be introduced by the wind into your bucket.

    I suggest you use a food grade plastic container with some sort of cover to protect the water after collection.

    It is always best to use RO water. So; Yes an RO filter is a great investment.

    Happy growing, lw – I❤️GM

  33. just wondering how long rainwater is good for when captured in an open bucket and will filtering of some kind help. Ps love your work.

  34. I have my Chemo 3 week old clones transplanted into 3 gallon pots in soil. I am growing under 1000 watt LED’s.
    The environment is staying at 70 deg F. I mixed 50% Seasoil (https://www.seasoil.com) with Promix HP. for the soil. I watered with a 400ppm nute mix until wet. After 1 week the soil is still very moist. Does the nute schedule take priority over the soil condition or should I apply nutes based on soil condition?

  35. First grow of my own,done 3 grows in CA I live in MA so it’s legal hear now so don’t have to go this year,I was told you should let the water sit for 24hrs or so to let something get out of it ( I think it was salts) I am using a hand dug well,any pointers,putting on YouTube Mass_Grass 2017

  36. I have well water and yes you have to make sure of your PH
    I run 4 – 1000 HPS High Spectrum lights with on the average of 17 girls I water them using just 5 gallons every day to water them all So far I’ve had good luck going on 3 years

  37. Got what I ordered in a timely manner. They look good but still haven’t popped them. Unable to download free manual???

  38. Even with modern technology; Flowering a 15 day old plant is not a good idea at all! I am not a fan of foliar feeding. I do not know anyone who foliar feeds with worm castings. Foliar feeding is only necessary when you develop an issue that has to be treated by a foliar concoction.

  39. anyone have any proof seaweed works as folia spray , my babies just been switched to flower after only 16 days grown in soil and frightened far too close with sensi ph automatic balance liquid feed under 600w halide in a tent 2 four ” carbon fillter fans with one going in heavily filtered and obligitory occilating fan , im still learning after 35 yrs , the advances in only a shor period with availiable nutrients has made things easier , even so this old man was brought to his knees on a lovely day filled with sunshine collecting worm casts with my bricklaying trowel and a shovel to spoil my babies , the things we do to help others gives such purpose and diversity for others to wonder . any advise would be helpful and welcome as sleep wont come till ive decided for or against folia seaweed benefits or not.

  40. Sorry but there is a hard and fast rule when it comes to watering. Always check them in the heat of the day and never water until they droop a little, then water the hell out of them. This is the technique I use to grow plants in the ground in a greenhouse that produce an average of 6 pounds 6 ounces each. My biggest plant was over 9 pounds.

  41. Dude u shouod know well water is going to have a diffrent neutrient base than city water. like your house is running on well water so you deffentantly should have had a back up fpr your water supply like a ph adjuster from the head shop or gardem stores
    before even ,dipping yoir solo cup in whatever medium uour usingyou should solutely make sure you have the number one thing your babies need to survive and that’s water without water and the correct water with the right alkaline and acidity are essential to you how your plant is going to turn out test the PH right now remember anything remember this one sentence a bud plant is the closest thing resembling a human being that is every single day they need to be tended to and taken care of, given the right nutrients, given the right time to rest, give them a cool off time woth noticeable temp drop of 10 degrees for regrowth. Moisture level level in your air is even the essential to how easily the plant can breathe so your water you need to take very seriously before you even stick a seed in the ground he should have a backup water plan good luck bud

  42. Well Jim,

    You really should follow the directions on the nutrients you bought. I also, invite you to join our support forum. We have Expert growers and informed members always will to help you to grow successfully. 🙂

  43. Hi sorry to bother you’s I have just grower painkiller first ever grow only got 30g of it I have 400w hps light now I have put reflective stuff on walls and floor indoor growing I now have 3 plants just starting veg 18/6 I have bio bizz grow/ topmax/bloom and heaven I need a water schedule also how much and help with a nutriant schedule if you’s could find it to help a fellow earthling nanoo nanoo ps mork and mindy ha ha x