Cannabis plants rely on a number of resources in order to thrive, but out of all of them, marijuana plants consume water in the highest quantity. This is because water plays a fundamental role in every part and biological process of the plant, from its roots to its canopy, all the way down to the cellular level. It is what facilitates photosynthesis, the process through which marijuana plants convert light into energy. Water also fills the cell wall, protecting the cellular membrane, which allows the plant to grow strong and support itself. Water is what allows the roots of a cannabis plant to extract vital nutrients from the soil and circulate them throughout the rest of the plant. During hot temperatures, water is what allows the plant to fight dehydration and wilting. In fact, the plant itself is mostly water—about 80% percent of the plant’s total composition.
Cannabis Watering Guide
Because so much water is involved in the developmental processes of cannabis, there are a number of issues that can present when your watering method fails to consider certain important elements. Of course, marijuana is a hearty weed—when it grows outside in natural soil, it tends to manage its watering needs fine enough on its own. However, the story is different when it is grown in pots, because it is subject to the risk of both under and over watering, among other things.
Despite the various factors that should be considered when watering your plant, there are some easy, common sense practices to live by. For example, a plant grown in a colder environment will need less water than one in a hot and dry climate. However, the soil you are watering should never be too wet. Rather, it should be just moist. If you water your soil just enough to keep it moist, this will prevent the roots from becoming waterlogged.
So long as your soil is kept consistently moist, there is no need for concern about overwatering. The amount of water your plant consumes may seem like a lot, but it's important to remember that a lot of that water gets evaporated through the leaves, absorbed by cells that fortify the plant, or used to deliver nutrients via the plant’s circulatory system.
The point of this guide is to help you to effectively cover all the ways that water impacts your cannabis grow. It will show you how to determine what kind of water to use, how often and how much to water, and how to ensure that your water most efficiently delivers nutrients. The following watering tips will set you up for a happy, hearty cannabis harvest.
Related: Growing Weed Using Hydroponics
Sourcing Your Water
Where you choose to source your water from matters. Optimally, you will be using either reverse osmosis or filtered water. However, most at home growers source their water supply straight from the tap. This makes sense for the obvious reasons: it’s convenient and there’s plenty of it. This is especially true for those living in sparsely populated areas. Growers don’t have to deal with the prospect of having to hunt down reverse osmosis systems at different gardening stores. The convenience and thriftiness of tap water is hard to ignore, especially when the journey to the kitchen sink is only a few steps away.
Unfortunately, not all tap waters are created equal. This is largely because, in addition to H20, your tap water also carries a significant amount of minerals. The mineral content varies from location to location; common minerals found in water are calcium, magnesium, and sodium, but there are plenty of others as well, and they present at varying levels. This is why it is difficult to really know what’s in your cannabis plant’s water without testing it first. Many municipalities offer water testing for free, but even so, there are many trace minerals cities might not even test for. Features such as geographic location, climate, and municipal filtration systems all impact the water’s mineral content. In fact, the factors that determine the quality of any given tap water are so high that it is difficult for regular growers to rely upon it consistently or predict its impact on a developing cannabis plant.
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Avoid Common Mistakes
Of course, you can grow perfectly fine cannabis solely on unfiltered tap water, but it’s a good idea to test it so that you know that your tap water is nourishing your marijuana plant with all the nutrients it needs to grow up happy and healthy. The measurement used to determine the ability of water to carry nutrients is known as the EC. The EC of tap water usually lies within the range of .2 to .8, although tap can sometimes measure higher than this. Additionally, you should be feeding your cannabis plants with water that has a pH level between 6 and 6.5. The pH level in tap water can also vary from source to source. Before you go out and buy an expensive nutrient mix or spend time meticulously measuring out the levels of nutrients for your plants, remember that regardless of the nutrient content of your water, those nutrients still need to present at specific ratios. Therefore, if you have all of the correct nutrients in your water but fail to add them at just the right ratios, you can cause nutrient lockouts, which prevent your plant from properly absorbing what it needs, or, in some cases, it can cause nutrient burns.
Always remember that your marijuana plant’s ability to effectively process water is also impacted by external conditions, regardless of what source you choose. Marijuana plants need their water to remain close to 68 degrees fahrenheit or 20 degrees celsius. Thermal shock to the root system becomes a real risk if the water you are using runs too hot or too cold. This condition can ruin the viability of your plant.
In addition to filtered, reverse osmosis, and tap water, you can also use rainwater to feed your cannabis plants. In order to catch and store rainwater, people generally use food-grade plastic barrels or other containers, and place some kind of screen across the top of the open barrels. This screen ensures that you catch only downpouring rain and no debris. While rainwater is an option for you, it is not necessarily healthier for your plant than regular tap water; the quality of rainwater depends upon the local air quality and surrounding pollution.
Related: How to Germinate Marijuana Seed
Timing Your Watering
Plants need a balanced amount of water at every stage of their development. This means you must set up a healthy, balanced watering schedule before your seed even germinates and grows into a sprout. This is because if you fail to water your plant with enough water and at the right times, you can dehydrate your plant to the point where its leaves and roots dry out, or cause an ungerminated seed to fail. Watering your plant too frequently can also potentially cause serious damage, as roots become susceptible to rot and waterlogging, preventing adequate absorption of nutrients. In light of the specific needs of your cannabis plant, here are some basic guidelines to help you schedule an effective watering regimen, according to where it is at in its stage of development.
Regardless if you are planting your seeds in a special starting soil or regular gardening soil, the best standard practice is to mist the soil that your seed is planted in. Rather than drowning your new plant with a pitcher-pour of water, try hydrating your cannabis by squirting it with a fine mist through a water bottle. This ensures that the soil is moist enough for the seed to properly hydrate, without weighing it down in excess water and heavy soil. At the early stages of your cannabis plant’s development, it is important to keep the soil light enough so that the germinating seed has a chance to breach the surface of the soil unimpeded. It is easy to overwater, so it is highly recommended to use a spray bottle during this early stage of development. Save your watering can for later, once your plant has safely established itself above ground. Using a germination jiffy pellet is also a great way to help ensure your seed receives the proper amount of moisture. The most important takeaway from this is to remember to water your seedling regularly, so that it is always moist but never drowned in water.
Once your plant has securely breached the soil, it is safe to allow the soil to dry up a bit at the surface before re-watering. This is because at this stage, the roots of the plant have grown deep enough into the growing medium, so that the plant can hydrate itself more efficiently than a new seedling. A more developed plant is a lot more forgiving than a new seedling, as it can handle a greater degree of stress incurred by both over and under watering. Special growing mediums that you can purchase—beyond regular soil—will often allow you to commit to watering every other day, or possibly at even greater intervals.
Use the sun to gauge your watering schedule. Try to work with it, rather than against it. Watering your marijuana plant in the morning will ensure that it has a full day to absorb the soil’s nutrients and properly allow photosynthesis. If you water only at night, you run the risk of leaving your plant susceptible to fungal overgrowth and waterlogging, because there has not been enough sun exposure to allow excess water to evaporate. Dry roots and overwatered roots are equally dangerous to the health of your plant. That is why it is important to monitor the frequency of your watering habits effectively. This is especially true if you are adding nutrients to your soil—proper watering will allow excess nutrients to run off, rather than causing an unhealthy and potentially toxic buildup of nutrients in your soil.
Determine the Quantity of Water:
Just like the quality of your water content, there are a number of factors that can determine the quantity of water that you need to sustain your cannabis plants. These factors include the type of soil you are using, the combination of nutrients being included (or lack thereof), the way that air is circulated throughout the plant’s environment, temperature, humidity, and degree of sun exposure. Additionally, the amount of water that you need to sustain a plant also depends upon the stage of development that your cannabis plant is in.
Not surprisingly, more developed cannabis plants will require more water in order to grow. This is partly due to evaporation—as the leaves on a cannabis plant grow, the surface area of the leaves provides a greater area from which water can be evaporated from the plant. The larger the surface area, the greater capacity the plant has to metabolize. This is because heat is generated from photosynthesis, which is maximized according to the surface area of a plant’s leaves. Overall, this means that the amount of water that a plant needs grows according to its size and stage of development. Although your watering schedule might keep the same timing for all of your plants, your younger and smaller plants will likely require a smaller quantity of water in comparison to your larger and older plants.
Despite this, an interesting thing worth noting is that a larger plant will often require you to water it less than younger, less developed plants and seedlings. The reason for this is that although larger plants require more water than smaller plants, the larger containers hold larger quantities of water for longer periods of time than smaller ones do. When a cannabis plant is in the late stage of its flowering phase, it will consume less water than other plants. Another cause for lightening up the water quantity is the climate. When conditions are humid, cannabis plants require less water—even if the temperature is high. This applies to both indoor and outdoor plants.
As with any relationship, the best way to meet your plant’s needs is to get to know it. Familiarize yourself with how heavy the pot is when the soil is moist but not soaked. This should be a good guide for you to measure against for the next time you water. As time goes by, water evaporates from the soil, leaving it lighter. If you fill a pot with dry soil and lift it, you will get a feel for how light your plant is when it’s dying for water, without actually killing your plant. The point of an exercise like this is to become conscious enough of your plant’s biological rhythms and physical changes to the point where determining the amount of water to give will come naturally to you.
Water with patience. Never dump a large quantity of water onto a plant all at once. Rather, pour gradually and evenly across the plant’s soil. It is important to water slowly, because it optimizes the capacity of your water to actually deliver nutrients from the soil. A large quantity dumped all at once will form channels within the soil, causing the water to drain too quickly from the pot. This makes it hard for the roots to properly hydrate and absorb important nutrients. The propensity for excess water to rush through the soil touches upon why it is important for your water to drain properly.
The water for your cannabis is draining properly if it is freely running through the soil to the bottom of the pot, rather than remaining stagnant inside. Proper drainage is especially important for potted marijuana plants, because it is just one of the factors that must be accounted for as part of creating an artificial environment for your plants. It is what prevents damage caused by overwatering, one of the most common ways to kill a plant. If water isn’t draining through the soil and out the bottom of the pot, it is likely that whatever material you are using for planting needs to go. That’s why we recommend what pro marijuana growers use, soft fabric pots that drain well and allow roots to breathe.
Water collected in the tray below your pot is a sign that you’re doing something right, but don’t hold onto it! Stagnant water allows for bacteria to flourish, and reusing that water can potentially cause damage to your marijuana.
How to Tell if There’s a Problem with Your Watering Method
An issue with watering will present signs in every system of the plant’s body, from leaves to roots. Here is what to look for:
- Leaf edges appear burnt
- Leaf tips appear burnt
- Curling under
- Stunted growth
- Leaves affected all over
- Upper leaves/newer growth affected
- Lower leaves/older growth affected
- Weak stems
- Stunted growth
- Foul odor
- Mushy texture
- Slow growing
Roots are the plant’s foundation, so sick roots will create an overall sick plant. Overwatering poses some of the most serious threats to root systems. Root damage can have dire consequences for your plant. It can be really tough to salvage an overwatered plant once the roots are affected, and some plants never fully recover. Rotting, waterlogged roots become hosts for bacteria and fungal growth, which can lead to an unpleasant variety of diseases.
Ways that You are Watering Wrong
Drown your cannabis in love, not water! Overwatering is the easiest, most common way to kill a plant. New growers are often unprepared for the way that such a simple, fundamental process can quickly turn lethal. Most gardeners have a psychological drive to nourish and provide for their cannabis, so people naturally reach for the watering can in order to feel that connection with the plant that they’ve put so much work into. Pay attention to how much and how often you water.
Drowning due to overwatering occurs as a result of an anaerobic reaction happening at the root level. Oxygen is typically stored in tiny air pockets, but excess water dampens them. As a result, there is no longer enough oxygen for the roots to absorb. As the roots weaken and die, the rest of the plant deteriorates and stops growing.
Remember, indoor and potted plants are much more susceptible to overwatering because they are completely dependent upon the environment you set up for them. This means that unlike outdoor plants, they cannot rely on the vastness of surrounding earth to absorb excess water. Even if the soil provides perfect drainage, a potted plant can still die from over frequent watering. Water that has been allowed to accumulate in potted soil—either from poor drainage or overwatering—will eventually cause rotting roots.
It is still possible to overwater cannabis that is grown in the ground. Soils vary widely from location to location, and some are less ideal for growing marijuana. Clay based soils are heavy and provide poor drainage, especially in humid areas with high precipitation. It’s also worth noting that the soil in some locations is too sandy, which allows water to drain too quickly for the roots to benefit. If your outdoor plants display signs of overwatering, it is best to space out your watering schedule. This will give your plants enough time to repair themselves.
While overwatering is primarily a root problem, you aren’t likely to notice signs of overwatering in the roots until it is much too late. After all, roots dwell below ground and behind the scenes. Instead, there are plenty of signs on other parts of the plant that will warn you that you are overwatering. If your plant is drooping, this means that too much water is making it sad and weak. This symptom is a tell-tale sign of overwatering and it’s easy to recognize—the entire plant will look as though the weight of the world is pulling it down. Whole leaves will curl under and sometimes fall off altogether. Wilting and drooping can be easily confused for one another, so it’s good to know the difference—especially because wilting is usually caused by underwatering, rather than overwatering. Signs of wilting occur in the tips of leaves rather than the entire leaf—tips will often yellow, curl under, and will be less firm than drooping leaves. Chlorosis, or yellowing of leaves, will sometimes occur in an overwatered plant, but even fully green leaves can still be suffering from overwatering.
All of these above-ground symptoms are happening because excess water is causing serious damage to the roots. Too much water flushes out nutrients before the roots have a chance to absorb what they need from the soil and water. If they’ve been sitting in perpetually soaked soil, the roots are eventually going to fall victim to fungal and bacterial growth. Root rot is a preventable tragedy.
Unless your plants are growing outside in a climate with heavy rain, the only way to address overwatering is to change your watering habits. This means that you need to water less—allow the soil to dry out. Although it may not feel intuitive (at first), marijuana plants really only need to be watered about two to three times a week. There are some variables that will require you to water more or less—for example, you will need more water if you are growing in a very dry climate, or less water if you are growing in large pots. Remember, larger pots store more water in the soil, and therefore need less of it.
One of the best ways to tell if you need to water less is to simply check the soil. Earlier sections of this article mentioned that soil should always feel moist but never wet. However, simply feeling the surface of the soil is not the most reliable indicator of your soil’s overall consistency. You can check your soil in the same way that you check a batch of baking brownies: take a toothpick or ruler and stick it a few inches into the soil and pull it out. If there’s no soil adhering to whatever you poked the soil with, that means that it is time to water (or take those brownies out of the oven).
Pay attention to the moisture of your soil, even between waterings. If your soil is perpetually soaked, you are overwatering and need to make some swift changes. If you are delivering water to your cannabis through an irrigation system, there are a couple ways you can limit water exposure; sometimes the distance between your plants and the spouts needs to be spaced out more, and sometimes the flow of water needs to be restricted. Whether you are watering by hand or using an irrigation system, you must nurse an overwatered plant by feeding it only tiny bits of water. If discolored, sick-looking roots begin to look stronger and white again, this is a sign that your plant is recovering.
People often mistakenly assume that they are watering too much or too frequently when really, they are dealing with drainage issues. Either the soil or the container it is planted in can cause excess water to accumulate. The next time you water, diagnose a drainage problem by watching how much water drains from the bottom of the pot. You should see about 20 percent of the water you added eventually drain out of the soil. If this isn’t happening, you know that water isn’t flowing properly. Sometimes the fix to a drainage problem is simple: Are there holes at the bottom of your pot? If not, add them using a sharp object or a power tool. Or you can use a convenient fabric pot, like professional cannabis growers prefer.
Sometimes the issue is with the soil—marijuana needs an aerated, coarse growing medium. You can increase oxygen flow and decrease dampness by occasionally poking the soil with a toothpick or pencil. If you notice that water is draining very slowly from the pot after watering, it is possible that the soil you are using is too dense. Try pouring water onto other mediums to see if there is a soil that will allow the water to run more freely. Regardless if your drainage issue is due to the soil or its container, you will most likely have to make adjustments to your pot or repot your cannabis altogether.
Overwatering is bound to eventually cause root rot. This dreaded condition occurs when roots are oxygen deprived. Too much of a good thing will block the roots from absorbing oxygen (waterlogging). Rot rot can also occur if there is not enough oxygen saturating the water. Either way, oxygen deprivation will cause the roots to decay and can easily destroy your plant.
Recover from Root Rot
As nasty as root rot is, there are ways to fight it once it hits. Gently remove the plant from the soil and examine the roots. With a scissor, clip the diseased parts from the rest of the plant and repot it in fresh soil. Another way to treat root rot is to add a few tablespoons of hydrogen peroxide to your water. This will attack the bacteria and fungus feeding off the sick roots. Additionally, the chemical makeup of hydrogen peroxide delivers a vital boost of oxygen to deprived roots.
If hydroponic growers are encountering root rot, there is an issue with aeration rather than overwatering. There are ways to adjust your setup that will improve aeration, such as introducing air stones or utilizing an air pump.
While the effects of underwatering are easier to bounce back from than those caused by overwatering, growers may underestimate the short and long term damage that dehydration imposes on a plant.
Underwatering prevents your marijuana plant from performing all of the biological processes that keep it alive. When dehydrated, cannabis will attempt to retain its water supply by closing its stomata. The stomata make up the plant’s respiratory system—tiny holes that allow water evaporation and the absorption of CO2. When they close, the process of evaporation and absorption of water is blocked. In an effort to survive, the plant will attempt to breathe faster—this expends vital energy that would otherwise allow growth and flowering. When dehydrated, the viability of a plant is at risk because it cannot perform photosynthesis.
As mentioned earlier in this article, water is the vehicle that delivers nutrients throughout the plant’s systems. When water is restricted, cannabis cannot extract nutrients from the soil, and it eventually develops a nutritional deficiency. Gardeners may attempt to treat a nutritionally depleted plant with fertilizers or special nutrient additives, not realizing that the symptoms their plant is exhibiting are due to dehydration. Without addressing the watering issue, extra fertilizers will do nothing to help the plant. This is dangerous, because if underwatering remains untreated, the plant’s condition will only worsen.
In order to keep itself from dying of thirst, a plant will preserve resources by diverting all of its energy to only its most basic functions. If a plant is underwatered during its vegetative phase, it will halt any new growth in its leaves and branches. In order to survive, it will first sacrifice its leaves, allowing them to wither and die. These consequences underscore the long term effects of underwatering. You can save a plant by giving it more water, but that temporary arrest of its functions can lead to a permanently stunted plant, smaller flowers, and an overall disappointing harvest.
Just like overwatering, underwatering is caused by bad watering habits more than anything else. Of course, plants grown outside are subject to droughts, dry climates, and water shortages. However, even in this case it is possible to monitor your plants for signs of dehydration and supplement them with the necessary water.
You Might Not be Watering Enough—Figure it Out
Paying attention to your cannabis will help you catch the signs of dehydration and treat them as early as possible. Early detection will reduce the likelihood of permanent effects like stunted growth. Sometimes it’s hard to notice the signs, since it takes a while to recognize delayed development. Additionally, some changes look similar to signs of overwatering.
Because the signs are easy to confuse, it’s important to look for symptoms that clearly differentiate themselves from ones due to overwatering. For example, a dehydrated cannabis plant will be wilted rather than droopy. Give your plant more water—if it looks healthier and quickly starts new growth, then you know that you’ve been underwatering.
Here are some other tell-tale signs that you aren’t watering enough:
- withered leaves
- bright discolorations in the leaves
- sudden onset of shriveling of leaves
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How to Rescue Your Underwatered Cannabis
Simply give your plant more water! The good news is that healing a dehydrated plant is easier than healing an overwatered plant. However, plants that have been underwatered to the brink of death require some special care. When nursing back to health, make sure that your water is pH balanced and free of any additives or fertilizers—as mentioned earlier, nutrient supplements will not address the core issue, which is dehydration. Wait for your plant to pick itself back up and for the wilting to cease before you make nutritional adjustments.
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What About pH?
If you are doing everything right but still noticing signs of poor watering in your cannabis, it’s probably time to check your pH level. There’s a seemingly endless array of causes for a sick plant, and the courses of treatment can be complicated and work-intensive. That’s why it is best to check your water’s pH level off the list before trying any of the more involved measures.
The good news about a pH problem with the water is that it is easy to diagnose and treat. When picking a pH tester, you have multiple options to choose from. Some gardeners prefer to use the liquid testers, but some may feel that the steps involved make testing more complicated than it needs to be. You can also use a digital reader, if you don’t mind paying a little extra. pH strips will also work, but be aware that strips are known to be less accurate. Choose the tester that works best for you.
If you suspect there is a pH issue in either your soil or water, test the water first. The same is true if you are noticing symptoms and suspect a different cause, such as a nutritional deficiency. For example, if you try to treat a nutritional deficiency first before considering the water, you may find yourself experimenting with various additives and mediums, only to find that your plant continues to decline. You may attempt to adjust the pH of your soil using similar measures, and end up further worsening the pH level of the soil. Before you start experimenting with worm castings, epsom salts, tea, and other additives, test the pH level of the water itself. This could be the source of your soil’s pH imbalance or any other symptoms your cannabis is exhibiting.
The pH level of tap water is often affected by municipal treatment systems. Cities will chlorinate the water in order to destroy pathogens, this also means that tap water can potentially be very damaging to your growing cannabis. This is especially true for those vital, vegetative growth stages. If you are going to use tap water, it is best to let your water sit for a day or two. This allows some of the chlorine to evaporate. Because of the way chlorine lowers the pH level, it is not recommended that you water your germinating seeds with tap water. The point of being conscious of your pH level is to ensure that the water you are using will enable your cannabis to absorb the nutrients that it needs.
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You’ve Got This
The takeaway from this guide should be that water is a fundamental part of your marijuana plant’s development, and therefore special care should be given to your watering methods. If you see something wrong with your plant, check the water. While there are many different ways that watering problems can manifest, the key is to pay attention to your plant, note its symptoms, and treat your plant as early as possible.