Crops need love too! Cannabis plants thrive when provided with the right amount of water and nutrients. Learn everything you need to know about watering your cannabis plants. No more guessing or worrying! Water plays a crucial role in keeping your marijuana plant healthy. Get tips from the experts at Leafly to keep your weed plants hydrated, and learn how to flush them properly.
How to water a cannabis plant
Cannabis is generally a resilient plant, and most strains can tolerate mistakes with feeding and watering to some extent. However, consistently delivering water and nutrients in the wrong concentrations or quantities can cause deep-rooted problems that can prove detrimental—or even fatal—to your crop.
Cannabis plants need abundant water, particularly in the flowering stage. As a general rule, plants should never be deprived of water for too long at any stage of their life cycle, as this can severely slow or even halt growth entirely. As well as this, depriving plants of water deprives them of nutrients, which not only slows growth but can lead to deficiencies.
Moderation is key
However, over-watering is a mistake many new growers make. Over-watering can lead to pythium (root rot), botrytis (grey mould) and powdery mildew, as well as causing nutrient toxicity and anaerobic (oxygenless) soil conditions in extreme cases. These issues can be disastrous, and are often extremely difficult for newbies to correct.
Most growers agree that soil should be allowed to dry out slightly between feeds—this lessens the risk of rot, mould and nutrient burn, and may also encourage the roots to grow denser. However, plants should always be watered before the roots start to dry out.
Finding the right balance is crucial, and it varies according to the strain (tropical sativas may be remarkably thirsty, while many indica strains abhor damp) and the size and growth stage of the plant—as well as other factors such as choice of medium.
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When should cannabis plants be watered?
There is some controversy over the best time of day to water cannabis plants. Most growers believe that cannabis should be watered at night time, but some argue that they should be watered earlier in the day.
Those that believe cannabis plants should be watered at night argue that in a natural environment, precipitation does not fall when the sun is shining, due to cloud cover. Many also state that if water droplets resting on the leaves are exposed to heat and bright light, they may act as “magnifying glasses” and burn the leaves.
It appears that this is just a myth, although leaf burn can occur through prolonged contact with some fertilisers. In any case, possible issues can be avoided altogether if care is taken to simply direct the water towards the soil and not the leaves!
On the other hand, watering earlier in the daytime allows the plant to utilise the available nutrients more effectively, as many of the fundamental processes of plant growth occur in sunlight. Leaving soil damp throughout the cooler hours of night can promote mould growth.
If growing outdoors, watering in the morning rather than the warmer afternoon appears to be optimal, as the rate of evaporation is slower. If growing indoors, watering at around the time lights are switched on may be preferable—while temperatures rise quickly with “hot” lights such as HPS, it usually takes some time for them to peak.
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How often should cannabis plants be watered?
At first, young plants will require small amounts of water at frequent intervals—up to twice per day if room temperatures are high and relative humidity is low. As they mature, they may be fed less frequently with greater quantities. Typically, large flowering plants must be fed at least once every 2-3 days.
The correct time to water plants should become apparent upon testing the moisture level of the growing medium. It should feel dry on top, but still somewhat damp below the surface. If it remains dry to the touch at depths of more than 5cm or so, plants are probably too dry.
This may all vary widely according to the drainage properties of the medium. For example, coco typically requires daily watering at first, then twice-daily as the plants increase in size; this is due to the fact that it retains water extremely well, so giving too much at once can saturate the medium and reduce airflow.
With experience, a visual check or simply testing the weight of the container will aid in determining when to feed, as a dry container obviously weighs substantially less than one full of water.
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A step-by-step guide to watering cannabis plants
First, prepare your equipment. You will need a source of water, a pH meter, pH down (this could be any strong acid), your chosen nutrients, and a watering can, hose or similar.
Water should be around room temperature—hot or cold water can shock and stress plants severely and sometimes irreparably. Most agree that water should be left to stand for 24 hours before use as this allows pH to be more accurately determined.
pH should be between 6.0-6.5 if growing in soil; if growing in soilless medium this value may be somewhat lower (coco prefers the 5.5-6.0 range). Use pH down to reduce pH if necessary, making sure to mix well. Incorrect pH can result in nutrient burn and various deficiencies, as roots are unable to process nutrients as effectively.
Add nutrients according to the manufacturer’s instructions, and mix thoroughly. Nutrient concentrations may be adjusted according to the strain and the stage of growth of the plant—such as when plants are young, or just after being transplanted.
Using a watering can, hose or similar, water the plants until runoff is visible in the trays beneath the pots. Many growers aim for around 10-20% of total water draining off, as this is believed to prevent nutrient build-up—but this is disputed.
Nutrient build-up occurs due to oversupply of nutrients (or reduced uptake by the roots due to overwatering or pH issues), and is fixable by flushing with pure water and not by adding more nutrient solution.
This basic guide should give novice growers all they need to successfully water and feed cannabis plants. However, adjustments to the basic principles may need to be made according to local climate, choice of strain, type of medium, and several other factors.
Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.
How Often Do I Water Indoor Marijuana Plants?
If you’re growing marijuana in soil or another growing medium like coco coir, you will have to hand-water your plants. Watering is an important part of growing cannabis indoors, and knowing how to water your plants will save you a lot of frustration!
How often do you give your cannabis water?
Well, you will want to water your marijuana whenever the top of the soil or growing medium starts to feel dry. I like to water when the medium feel dry up to my first knuckle, or about an inch.
- Soil – Water plants when the soil feels dry up to your first knuckle (or if the pot feels light).
- Coco Coir – Aim to water plants every 1-2 days. If coco is staying wet for 3+ days, try giving less water at a time until plants get bigger and start drinking more. Don’t wait for your coco coir to dry out, but don’t water if the top inch feels “wet”. If the container feels light, it’s definitely time to water!
How to water cannabis properly (when using a well-draining potting mixture with liquid nutrients)…
In soil, wait until the topsoil feels dry about an inch deep (up to your first knuckle – just use your finger to poke a hole in the soil and see if it feels dry).
In coco coir, you want to water every 1-2 days if possible and adjust the amount of water you give accordingly. The top inch doesn’t need to completely dry out between waterings.
If you’re regularly adding nutrients in the water, give enough water each time that you get 10-20% extra runoff water drain out the bottom of your pot. This prevents a buildup in the potting mixture because otherwise, you are continuously adding more nutrients to the system.
Go back to step 1. Note: If water takes a long time to come out the bottom, or if pots take longer than 5 days to dry out before the next watering, you may actually have a problem with drainage (more info below) or need to give less water at a time. If your plants are very small compared to the container they’re in, give water more sparingly until plants get bigger.
Growing in Super Soil?
- If you’re growing in super soil or another heavily amended potting mix, you may not need to add extra nutrients to the water because your plants can get all their nutrients directly from the soil.
- Any time you’re not adding extra nutrients in the water, you want to avoid getting runoff water because it will carry away some of the nutrients in the soil.
- Watering until you get runoff is important when using liquid nutrients because it helps prevent nutrient build up, but with super soil try to give just enough water that you wet the entire medium but don’t get extra water coming out the bottom.
Some growers swear by the “lift the pot” method to decide when to water your plants (basically wait until your pot feels “light” since the plants have used up all the water). It’s up to you to decide what’s easier for you.
I usually water my cannabis with a 1-gallon water jug for small grows, or 5-gallon jugs for larger ones. Runoff water is collected in the trays and after a few minutes I suck it all up with a small wet vac .
How to Provide the Water
When I first started growing, I gave my plants water using a watering can. A watering can works great, but it’s hard to water a bunch of plants with one watering can because you have to keep filling it up.
An old-fashioned watering can will get the job done, but they typically don’t hold a lot of water at a time, which is inconvenient if you’re growing a lot of plants
I personally like using a Battery Operated Liquid Transfer Pump to water the plants. You can pump water from a bigger container to your plants. This is a 3-gallon water container from Wal-Mart, and the pump just reaches the bottom.
My grow tent is 2 feet deep and this reaches the plants in the back. However, I don’t think the tube is long enough to reach the back if your space is deeper than that.
Some growers set up elaborate drip feeds to pump water if they have a lot of plants they can’t easily reach, both homemade or pre-made.
Let us know if there’s something we missed. Growers get creative!
How to Collect Runoff Water
It’s important to keep plants on saucers or trays so you can remove the runoff water. You can collect the saucers one by one and dump them out, but that also gets inconvenient with many plants.
It’s inconvenient to empty saucers one by one if you have a bunch of plants, but you don’t want to leave plants sitting in runoff water
If you put your plant on plastic trays, and then put the trays on a slight incline by putting something small underneath in the back, it will catch all the runoff water and cause it to drain to the front. The item in the back only needs to be about half an inch thick, for example a piece of plywood. However, if you can find something more water-resistant, like plastic, that’s even better.
These 1’x2′ plastic plant trays work well if they fit your space. You can fit four of them in a 2’x4′ grow tent (this is the grow tent I use) with up to two plants each as long as your plant containers are 11″ wide or smaller at the base.
Put trays on a slight incline by placing something underneath the tray in the back. This causes all the water to come to the front for easier collection. Each of these trays has a small plastic board (which we found around the house from something else) under the back. Anything that’s about half an inch high will do the trick. These particular trays accommodate plant containers up to 11″ wide at the base.
Not sure how to remove runoff water after watering your marijuana? Wet vacuums can be a great choice, especially if you already have one in the house. I didn’t have one, so I got Bucket Head attachment which can turn any standard 5-gallon bucket into a wet vac. You can buy one online but it’s $10-15 cheaper if you get it in person at a Home Depot. Another similar option is the Power Lid, though it’s also a bit pricey.
A downside to the Bucket Head is it’s a little loud, just like most wet vacs. Luckily you only need to use it for a few minutes after watering your plants!
Removing runoff water is a great start to make sure you are watering your cannabis plants perfectly, but it’s also important to…
Make Sure Pots Have Good Drainage
It’s very important to make sure that water can drain freely from the bottom of the pot, otherwise, the plant can get waterlogged and become overwatered (causing the plant to droop).
In addition to making sure the actual container has drainage (holes on the bottom, or some other way for extra water to escape), it’s also important to make sure your growing medium drains freely. If it takes several minutes for the water to come out the bottom of your pot when you water, it means that there isn’t enough drainage in the actual growing medium (it’s too dense, so water is having a hard time getting through).
How to improve the drainage of your growing medium
- Never use dirt you find outside. Chances are it does not have the correct properties for vigorous cannabis growth.
- Mix in extra perlite to loosen the soil and allow water to drain through more easily.
- Bark or wood chips are not the best choice for growing cannabis plants, even though they’re sometimes recommended to improve drainage in soil for some types of plants. On that note, avoid using soil that contains bark or wood chips. What makes soil good or bad for growing cannabis?
- Use Smart pots – these fabric pots help get oxygen to your roots (which gives you faster growth) and this type of pot makes it harder to overwater your plants. A cannabis plant growing in a tan fabric smart pot is pictured to the right.
This is an example of great soil for growing for cannabis – rich, composted, and well-draining
Composted super soil lets you grow organic marijuana without any extra fertilizers or nutrients
Watering Too Often? Barely at All?
In the beginning of your grow, you will likely be watering your marijuana plants every couple of days. Watering every 2-3 days is optimal for a young plant. If it’s taking too long for your plant to dry out, you may need to give less water at a time until the plant is growing faster.
If you feel like you are watering your plants too often, you may need to give more water at a time. You can also move plants into a bigger pot (which holds water for longer).
If plants take longer than 3-4 days to dry, make sure your potting mixture has good drainage and consider giving less water at a time
If plants are drying out in 1 day or less, try giving more water at a time or transplanting to a bigger pot
Speaking of pot size, it is generally best to start young cannabis plants in relatively small containers (like a solo cup with a few holes cut out of the bottom for drainage), and move plants into bigger containers as they get bigger. Starting in smaller containers makes it a lot harder to overwater your plants when they’re young, and makes it easier to flush plants and/or respond to problems if they occur.
That being said, you can plant your seeds right into their final container. Just be careful not to overwater your seedlings at first if they’re in a big container as they’re not drinking much water in the beginning.
If you started your plants in a solo cup, I’d recommend moving to a bigger pot once the plant is a week or two old, as soon as the leaves reach the edges of the solo cup.
10-20% Extra Runoff Every Time You Water (if you’re providing nutrients in the water)
Every time you water your plants, make sure that you provide enough water to get about 10-20% extra run-off out the bottom of the container, especially if you’re feeding additional nutrients in the water.
Sometimes soil and soilless growing mediums like coco coir start to collect natural salts from fertilizers that never get washed out.
These built-up salts can eventually cause nutrient problems, pH problems, and nutrient lock-out if they’re not removed on a regular basis.
Making sure you keep adding water until you get run-off is also a great way to make sure that your plants are draining properly.
Plus, this practice will immediately alert you to any drainage problems, (as mentioned earlier, cannabis likes well-draining soil) because you’ll be able to notice if the water takes a long time to come out the bottom, or doesn’t come out at all.
Different Nutrients for Different Stages of Life
First, make sure you’re using proper cannabis nutrients for your growing medium. They should be formulated for a plant like tomatoes, and they should have a different feeding schedule for the Vegetative (Grow) and Flowering (Bloom) stage.
If using nutrients on a regular basis by adding them to your water, it’s generally a good idea to give your cannabis plants nutrients every watering. This ensures the amount of nutrients in the plant root zone is kept relatively stable. If you notice the tips of leaves getting burnt from nutrient burn, it may mean you need to lower your overall strength of nutrients. Most nutrient recommendations on the side of the bottle are too strong for cannabis plants, and should be cut in half unless plants appear pale or lime green (which means they want higher levels of nutrients overall).
If Growing in Composted or Amended Soil, Give Just Enough Water That the Soil is Wet All the Way Through
When growing in composted and amended soil, the soil itself is made to slowly provide nutrients to your plant throughout its life. However, if you’re regularly watering until you get a significant amount of runoff, you’ll also be washing away some of your nutrients.
This is good when the plant is getting the nutrients directly in the water, to avoid unwanted buildup in the soil, but try to avoid a lot of extra runoff if you want your nutrients in the container to last until harvest.
Therefore, when growing in amended soil you should only water until you get just a drop or two of water runoff out the bottom. You want to ensure you gave enough water to reach the bottom of the pot without letting a significant amount of water run out the bottom.
Proper watering practices will greatly help reduce the amount of salt buildup and prevent nutrition problems from occurring.
If your cannabis plants shows signs of drooping, often the plant is getting too much or too little water, but not always. Drooping can be caused by….
- Too much water at a time, or giving water too often
- Not enough water at a time, or giving water too infrequently
- Drooping can also occur in hot conditions, or when it’s very humid or dry because the plant isn’t able to move water properly through the plant.
- Plants sometimes get droopy if they are given a lot of water after being allowed to dry out for too long, due to the stress of the water pressure quickly changing at the roots.
- Drooping is almost always associated with something going on at the roots, but plants also tend to put their leaves down a bit right before the lights go off, as if they’re preparing to “sleep” for the night. That can sometimes be mistaken as drooping when its actually part of the plant’s natural rhythm.
In order to prevent over or under-watering, make sure you water thoroughly every time (don’t just water a tiny spot in the middle of the pot unless you plant is very small for the container). You should be getting 10-20% extra runoff water every time if you’re adding nutrients in the water. In soil, wait to water again until the top inch of the growing medium feels dry, up to your first knuckle or so. In coco coir, aim to water the plants every 1-3 days if possible, and don’t let the top completely dry out between waterings.
Underwatered Marijuana Plants
- Wilting is the first sign of underwaterd marijuana plants
- Leaves are limp and lifeless, they may seem dry or even “crispy”
- Will eventually lead to plant death if not corrected
Overwatered Marijuana Plants
- Drooping / Curling is the first sign of overwaterd marijuana plants
- Leaves are firm and curled down all the way from the stem to the leaf
- Will eventually lead to leaf yellowing and other signs of nutrient problems if not corrected
If your plant is experiencing “the claw” and not just normal drooping (like the ends of leaves are just pointing down like talons, then you may actually have a nitrogen toxicity (too much nitrogen).
Nitrogen Toxicity (“The Claw,” tips bent down, dark leaves)
Learn more about Nitrogen Toxicity
How to water and flush marijuana plants
Like all plants, cannabis requires water in order to perform its basic functions. Water helps plants absorb nutrients from the soil and then moves up the plant and into the leaves, and without it, the plant can’t survive. But giving a marijuana plant the proper amount of water may be more difficult than you think.
There isn’t an exact science for watering a weed plant. You can’t observe the roots in most cases to see if they need water. Also, a plant is constantly growing and the climate it’s in will fluctuate, so the amount of water it needs constantly changes.
Here are some tried-and-true tips to keep your weed plants healthy and properly hydrated.
How often should you water marijuana plants?
A common mistake first-time growers make is to overwater marijuana plants. A cycle of wet and dry is healthy and necessary for the roots of a plant to grow out and reach deeper into the soil.
Additionally, roots pull in oxygen as soil dries and when soil is too wet, the plant can’t pull in oxygen efficiently and essentially can’t breathe.
Below are general estimates and are meant to give growers a rough sense of frequency of waterings; if a plant needs water and it falls outside of these ranges, water it.
|Plant stage||Water every # of days|
How to tell if a cannabis plant needs watering
The best ways to tell if a weed plant needs water is to:
- Stick a finger 1-2 inches into the soil—if it’s wet, hold off; if it’s dry, it’s time to water.
- You can also pick up a pot and feel its weight to determine if it needs water. This will take some experience—be sure to lift up your pots after watering to get a feel for how heavy they are when full of water. This will also give you a sense of what a light, dry, plant feels like.
An under-watered marijuana plant looks droopy and weak, with yellow or brown leaves; there is no strength in the leaves and they look lifeless.
Leaves of an overwatered plant look slightly similar in that they droop, except the leaves will be dark green and the leaf tips will be curled.
Note how often you water plants and write it down in a log. Get your marijuana plants on a watering schedule—as they grow out of the seedling stage, watering every two to three days is ideal.
Keep in mind that as plants get bigger, they will need more water and need to be watered more frequently.
When growing weed outdoors, you’ll need to water more often as the weather gets hotter and less often as it cools.
When you find the sweet spot between too wet and too dry, your plants will flourish.
How much should you water marijuana plants?
The amount of water your marijuana plants need depends on a few factors:
- Size of plant
- Outside temperature
- Overall health
- Stage of growth
You want to water a plant enough to soak all the soil in the pot. Water should pool up on the surface of the soil when you’re watering, and come out the drainage holes in the bottom of the pot after a couple seconds. If water sits on the surface of the soil, that means it’s too wet and doesn’t need more water.
If a weed plant is very dry, water will run straight through the soil and pot and quickly come out the drainage holes. If this happens, water the plant a little bit and then come back to it after 15-20 minutes and water it again, and maybe even a third time. This allows the soil to slowly absorb water until all of it is thoroughly wet.
Roots are constantly on the hunt for water as they grow and stretch out. As a plant gets bigger, so should the watering radius—the area around the stalk of the plant that you water. Doing this will help guide roots to the edges of the pot as they seek available nutrients in soil.
Watering too far away from the roots can create standing water, which can lead to root rot, mold, and pest issues.
Is your container the right size?
To properly water a cannabis plant, it needs to be in the correct size container, or a big enough hole if it’s in the ground. If a pot is too big, the plant’s roots can’t drink water where they don’t reach. If the roots aren’t absorbing water, water will sit in soil and take a long time to evaporate, which can promote root rot and unwanted insects and fungus.
Conversely, if a container is too small, the roots won’t be able to stretch out, which can stunt the growth of a plant. Less soil also meant you’ll need to water the plant all the time, which will add labor.
Ideally, cannabis plants should start in a small pot and progress to bigger and bigger pots as they outgrow each container. For example, you can start a seedling or clone in a 4″ or 1-gallon pot, then move on to a 2-gallon, 5-gallon, 10-gallon, and so on.
Plants are ready to transplant when a healthy root structure encompasses most of the soil and the roots aren’t bound. When transplanting, take time to look at the quality of the roots: Bright white roots with a strong, thick structure is a sign plants are getting watered correctly.
What is flushing?
Flushing is an important part of the marijuana growing process, when you stop giving a marijuana plant nutrients and give it straight water. This is done to flush out nutrients that may have built up in a plant during its life.
Flushing is done for about a week before harvest, at the end of a plant’s flowering stage when buds are almost ready to cut down.
A flush can also be done to clear plants of nutrients if they have a nutrient imbalance, such as nutrient lockout, when your plants are overloaded with nutrients and unable to absorb new ones.
How to flush weed plants
Flushing marijuana plants before harvest
The final flush should occur for a week or so before you cut down weed plants for harvesting. Water your plants with the same amount as you normally would, but only with water. This will force the plant to use the nutrients stored within it—if its nutrient reserves are not used or broken down, it could affect the quality of your harvested buds.
By looking at the trichomes on marijuana plants, you’ll be able to tell when the plants are ready for a flush—begin when they start turning milky.
Different growing mediums require different flushing timeframes before harvest:
- Soil: 7-10 days
- Rockwool and coco: 7 days
- Hydroponics: 5-7 days
If growing in amended organic soil, it is not recommended to flush plants. This is because the soil already holds all the nutrients the plant needs to thrive, and by flooding the soil you can wash away and damage the complex ecosystem that you’ve worked hard to develop.
When to stop watering before harvest
Water your marijuana plants as normal when in the flushing phase—don’t let them get too dry or too wet. Make sure not to harvest dry or wilting weed plants—they should be nice and healthy when you cut them down.