Watering cannabis plants how-to guide

17/09/2021

watering cannabis plants and seedlings how to water your plants Dutch Passion

Watering cannabis ought to sound like it’s one of the simplest things to get right in your grow room. However, after several decades specialising in cannabis seeds, Dutch Passion have found that over-watering (and over-feeding) cannabis plants is one of the most frequent problems seen in the grow room especially by less experienced growers. In simple terms cannabis roots will not grow well in waterlogged soil conditions due to lack of oxygen.

If the cannabis roots can’t grow healthily then nor can the rest of the plant. Everything from mineral/nutrient uptake to respiration is affected and in the worst cases growth can stop and plant damage can be terminal. The flawed, but perhaps partially understandable logic from the less experienced cannabis grower is that more water/nutrients will result in larger cannabis plants.

In fact the largest, healthiest cannabis plants can only reach their full genetic potential/potency if they are neither overwatered nor over-fed. This is equally true whether growing autoflowering cannabis seeds or feminised seeds, the same principles apply. Read on for some expert tips and advice on how to water your cannabis plants and avoid the pitfalls of under-watering and over-watering your cannabis plants.

How much water do cannabis plants need?

One of the difficulties with watering cannabis plants is that it is far from a precise science. Larger cannabis plants need more water than smaller plants.

The amount of watering required will be affected by ambient temperatures, humidity, airflow as well as the type of grow method, the age of your plant and other factors such as the plant container size/type, indoor vs outdoor etc.

An expert grower may have the practical experience to process all the variables and know the right amount of water to provide at any given point in the cannabis plant life cycle.

For the rest of us, useful hands-on tips, gadget recommendations and solid advice can mean the difference between a successful harvest and a poor one compromised through over/under watering.

Bubba Island Kush cannabis plant with water drops

One key piece of advice to any grower that struggles with over/over-watering their plants is to buy a tensiometer. These measure soil water tension, allowing soil moisture levels to be determined accurately. Many top growers have a tensiometer for each plant. The probe is buried beneath the soil, and the moisture measurement slowly changes as the soil becomes dryer. They are easy to use and allow you to keep your plants in the moisture sweet-spot.

Here are some key factors to watch for an optimal water intake.

Higher temperatures cause higher levels of transpiration in your cannabis plants, especially in dry (low humidity) environments. Transpiration is the process where the plant releases water vapour through the stomata (pores) in the leaf tissue.

Plants grown in low humidity environments/regions transpire water at a greater rate than plants in high humidity conditions. In simple terms, cannabis plants ‘dry out’ more easily in low humidity conditions.

Ensuring sufficient water can be an issue especially for those growing monster outdoor plants in a desert-style environment with a steady, drying breeze. Such plants can require 25 litres /5 gallons or more per day.

Indoor water consumption rates generally max out at around 5 litres/1 gallon per day for most growers, this assumes a fairly large plant approaching harvest grown in hydro. Outdoor grown plants can require several times this amount.

Indoor growers have the opportunity to optimise light levels, nutrition and their grow environment. Steady temperatures, good ventilation/air flow and effective humidity control all need to be optimised in order to push your plants to the max.

Note that in late bloom many growers aim for grow room humidity levels to be reduced to 40-50% (reducing mold & bud rot risks). This can be a challenge with large plants often at their thirstiest stage of their grow cycle with high rates of transpiration.

Large soil-grown plants in 30-50 litre containers can take around 5 litres of water/feed towards the end of bloom. More for those with the very largest plants.

If growing correctly in coco fibre or hydro, the increased root aeration levels (compared to soil/compost) mean overwatering shouldn’t be an issue.

Soil has the benefit of a certain level of natural pH buffering. Meaning you won’t have to worry about pH nutrient checks in the same way that hydro or coco growers might. But soil growers do need to pay attention to under-watering and over-watering their cannabis plants.

By far, the easiest way to keep your plants in the soil-moisture sweet spot is to use a tensiometer. This takes all the guesswork out of the equation (container size, ambient temperature/humidity, plant size/stage).

Small cannabis plants need less water/nutrients than a large harvest-ready plant. And seedlings need less nutrition and water than a small /medium sized plant.

Germinate a cannabis seed in a 10-litre container of moist soil and you may not need to water it (other than perhaps a light misting or surface sprinkle) for a week or two.

In the weeks after water requirements steadily increase eventually necessitating daily watering as the plants mature.

Some types of grow containers, such as felt sacks & airpots have a more aerated design than traditional plain plastic containers. This extra aeration supports superior root growth but also infers greater moisture loss from the soil compared to a traditional container. This would mean perhaps more watering would be required compared to a traditional less-aerated container of the same volume.

Larger containers contain a greater mass of grow medium and moisture than smaller containers. Many indoor growers prefer to grow in large containers, sometimes 50 litres/10 gallons+ of grow medium.

Such large containers offer the plants a large reservoir of both nutrition and moisture. Meaning that (especially with small/medium plants) watering frequency may not need to be as frequent as it would with a smaller container.

If growing large outdoor cannabis plants in small containers in a hot climate you may need to water daily with several litres of fluid. Sometimes you may need to water several times each day.

Larger grow containers may not be convenient for everyone but they can contribute to a lower-maintenance grow. Especially if combined with slow-release organic nutrients such as those from BioTabs. These can result in a ‘water-only’ grow method for much of the grow. And if you grow indoors in large 50+ litre containers you may not need to water too frequently at the start of the grow.

Plants that are slow & small require less watering. As they grow their enlarging root system is gradually able to use more water/nutrition. But remember, cannabis roots grow slower in heavy, waterlogged soil. Many prefer to wait until the soil is starting to dry out before re-watering, this avoids the risks of over-watering. The most accurate way to determine the moisture content of your soil is with a tensiometer.

How often to water weed plants?

Mokum's Tulip (bottom plants) on a wilma drip system with a rockwool plug with coco inside and clay pebbles around.

Monitoring your soil moisture content with a tensiometer is the best approach if you are in anyway uncertain about watering frequency. For small plants in a large container of moist soil this may mean only infrequent light watering is required. For harvest ready soil-grown monsters you may need to provide several litres per day.

Many manage without a tensiometer, perhaps assessing the weight of their container as a guide to when watering is needed. Others have a routine established over several years for their particular grow and preferred container.

Best time of the day to water cannabis plants

Many theories exist! Perhaps the best advice is to water your plants when the soil requires it. One scientific observation is that cannabis requires less water during periods of darkness – due to lower transpiration rates.

For that reason, some feel that watering in the early/middle part of the daytime period is favourable. This delivers the water when it is most needed.

But it’s also worth noting that cannabis evolved naturally without a defined watering schedule. This infers that, so long as the soil has a moisture level within the normal range, the precise moment of watering may not be that critical.

That said, many outdoor growers have established beliefs about when to water. Some historically prefer to water their plants at the start of the day to ensure moist soil for the day ahead. Others prefer to water their outdoor plants in the evening, feeling that the cool night conditions will preserve the water for the following days requirements.

Under watering symptoms and cure

Under watered cannabis will often have wilting leaves and a drooping, lifeless appearance. The leaves will hang downwards with a limp appearance. The experienced grower won’t confuse the symptoms of overwatering (clawed leaves, described below) with under watered cannabis.

One other clue to diagnosing under-watered cannabis is to take a quick look at the grow medium. If you’re grow cannabis in soil which feels bone dry it’s a sure sign that the cannabis roots have very little available moisture.

Fan leaves may also show some brown or yellow discolouration when under-watered. The simple solution is to water your cannabis plants.

Underwatering cannabis plants how to water them Dutch Passion cannabis seeds

Useful tips for under-watered cannabis plants

Ensure even application of water

When applying water, it is important to cover the surface area of the grow medium with equal amounts of water. Don’t just water the centre of the grow container, water the edges equally as well.

A watering can with a sprinkler will give more equal watering than dumping all the water onto a small central area of your container. Apply the water slowly, allowing even application. This also avoids damaging and disturbing the sub-soil root structure if all the water is suddenly tipped onto a small area of the surface.

Monitor the weight of your plant container to assess when to water

One other useful tip is for growers to monitor the weight of their plant container when wet and dry. This can provide a useful future guide for when the plant needs watering. Monitoring the weight of your plant container can help prevent the less experienced grower from routinely over-watering their cannabis plants.

Use a hygrometer

A hygrometer is a device with a probe that is inserted into your grow container. Hygrometers are popular with soil growers since they provide a clear reading of sub-surface water/moisture levels.

They are available from companies such as Blumat. Many growers, including highly experienced master growers as well as rookies, will have a hygrometer in each grow container to give an ongoing moisture readout.

A hygrometer removes all the guesswork from watering and is recommended to any grower that has struggled with cannabis plant watering. This is a useful tool to prevent growers routinely over watering their cannabis plants, one of the most common grower mistakes, especially by less experienced growers.

Under-watering is generally less damaging to cannabis than over-watering

One useful tip, especially for less experienced growers is to err on the side of under-watering your plants. This is less troublesome than permanently over-watering your plants and leaving the roots in a continuously waterlogged state. Cannabis plants grown in waterlogged soil are often permanently stunted and never reach their full potential.

Over watering symptoms and cure

Over watered cannabis will often have leaves that appear to have a healthy green colour. The cannabis leaves tend to claw inwards, rather than displaying the limp and wilted appearance of an under watered plant. A quick check of the grow medium is also a good way to determine if your plants have been overwatered.

Typically, the grow medium will be excessively wet with more moisture than the cannabis roots require. At the same time, the grow medium may also be poorly oxygenated which compounds the problems and the slow rates of growth. In the worst cases, a chronically over-watered cannabis plants is permanently stunted and never reaches anywhere near her full genetic potential.

After many years supplying cannabis seeds to home growers and professional growers, it is clear that many growers tend to regularly over-water their plants and compromise final harvest quality/quantity as a result.

Overwatering cannabis plants curled down leave tips limp wilted

Useful tips for over-watered cannabis plants

Avoid leaving your cannabis plants sitting in run-off water

Leaving your plants sitting in run-off water is generally considered poor grow room practice. Run-off water quickly becomes stale and can be a breeding ground for bacteria, mold and pests. Pour it away or soak it up with a sponge and dispose of it.

Check your grow medium is draining correctly

If you grow in a good brand of light soil or coco fibre (which has a naturally highly aerated structure) it’s unlikely that you will have any drainage issues. But less experienced growers using e.g. a home-made soil blend may find poor drainage properties can result in their plant roots sitting in waterlogged conditions.

If it takes several minutes for water to stop flowing after a good watering, it could be a sign that your mixture is too heavy. Be sure to use a more aerated grow medium in future grows, perhaps with added perlite or coco fibre.

Using air pots of fabric grow sacks is another way to increase oxygenation levels in the root zone. But these should be used in conjunction with an aerated grow medium, rather than in place of an aerated grow medium.

Remember that cannabis plants grow at different speeds

Some cannabis strains, as well as individual phenotypes, will grow at their own pace. This may be a result of the genetics or a response to grow conditions. In cool conditions, clones of the same strain can grow at quite different speeds to those in optimised conditions. The experienced cannabis grower will understand and allow for the subtle changes to plant appetite and will respond accordingly, being careful to avoid overwatering.

Evaluate your climate and act accordingly

A hot, dry low humidity environment will cause your plants to consume more water. In contrast, your plants would consume less water in a cooler higher humidity environment. It is therefore very important to keep a close eye on both your min/max temperature and humidity. You can adjust your watering amounts accordingly to allow the right amount of water for the corresponding conditions.

What type of water is best-suited for cannabis

Cannabis plants have coped well with rainwater for millennia. They are tough, adaptable, and hardy plants that can cope with a range of conditions and water types. Sometimes we must remind ourselves that cannabis grows very well without human supervision! But it’s always worth a quick look at the various water types and how they can affect cannabis cultivation.

Using tap water to water your cannabis plants

Tap water for cannabis

Most growers use tap water for cannabis. The level of acidity/alkalinity is known as pH. This is usually a neutral pH value of 7, but it can vary from city to city and water supply to water supply. Soil growers rarely worry too much about pH since soil is a natural buffer.

But it’s an expensive way to water your plants. Cannabis growers that feel their tap water supply is too inconsistent often invest in a reverse osmosis system to purify their own water.

But those growing cannabis hydroponically (or in coco fibre) will check incoming water pH carefully with a calibrated pH meter and adjust to keep it around the pH5.6-5.8 area. At these optimised pH levels, all the minerals in water are bio-available for absorption.

Outside of a useable pH, minerals may be difficult for the plant to easily absorb even if they are present. This is known as nutrient lockout.

Bottled water for cannabis

Some growers use their favoured supply of bottled water if they have reservations about the quality of the local tap water. Often, they feel that certain natural water springs deliver favourable mineral contents.

However, this is an expensive way to water your plants. Cannabis growers that feel their tap water supply is too inconsistent often invest in a reverse osmosis system to purify their own water.

Hydroponic cannabis growers often like to use reverse osmosis water to remove minerals from the incoming water supply. This allows them the ‘blank canvas’ of precisely controlling all the minerals which are subsequently introduced to their grow system

Water collection system

Some organic growers like to collect natural rainwater and use it for watering their cannabis plants. The logic is that the water will be free of chlorine and other potential contaminants introduced during water treatment.

The downside of using rainwater is that some consider it to be less pure than top water, especially when it has fallen in large industrial cities through a potentially dirty atmosphere.

Some people are also concerned about possible biological impurities such as bugs, spores, or pest larvae.

Re-using clean water from the dehumidifier

Most growers use dehumidifiers to extract the moisture out of the air in order to keep a stable humidity level or ‘RH’. When cannabis plants grow, much of the liquid water that is given to them is returned to the atmosphere via transpiration (moisture release via the stomata on the leaves). You can use a dehumidifier to collect the water that was extracted from the air. This water can be re-used to water the plants again, perhaps alongside tap water. Note that dehumidified water contains less (or no) minerals compared to tap water.

What is the best way to water cannabis?

hand watering vs self watering system cannabis dutch passion seed company

Several different options are available.

Spraying:

Spraying cannabis with water (or dilute nutrients) is a proven way to deliver nutrients directly to the plant via foliar absorption. Whilst ‘foliar feeding’ can be done safely at most stages of plant life (foliar feeding is sometimes discontinued in late bloom to minimise bud rot possibilities) it is particularly popular with seedlings and cuttings which may lack the extensive cannabis root system required.

A gentle spray can help the seedling/cutting maintain the correct levels of water uptake. Watering young plants with a heavy water flow (e.g. from a watering can or hose) may damage the delicate stems/branches – another good reason to consider occasional spraying.

Manual watering:

Manually watering cannabis plants is usually done by a watering can, hose or similar. Care should be taken to apply the water evenly across the surface of the grow substrate.

The goal is to ensure the water/nutrients are evenly distributed throughout the grow medium. Keeping your cannabis plants in the nutrient sweet-spot, free from the perils of over/under feeding from seedling to harvest is the optimised approach.

Use of aerated grow containers such as air pots, felts sacks etc helps ensure an oxygenated root ball. Cannabis growth is slowed down in heavily water-logged soil.

Drip irrigation:

Drip irrigation may seem more complex and (initially) expensive but is the preferred approach especially for those growing larger plant numbers and those that want maximum automation with minimum effort.

Often controlled by an app (or a control unit), drip irrigation ensures each plant gets the right level of water/nutrients meaning less chance of over/under watering or nutrient mismanagement.

Precision control is one advantage of drip irrigation, potentially saving water consumption in larger grow operations. This extra control allows optimised plant growth and reduces manual effort from the grower.

Hand-watering vs auto-watering systems for cannabis

Both hand-watering and auto-watering systems for cannabis growing deliver great results when done well.

Hand watering is often preferred by those seeking the simple approach, or perhaps those with just a few plants to care for.

Auto-watering systems can be the only practical and realistic option for those growing cannabis in commercial quantities such as legal, licensed growers. Whether hand-watering or auto-watering cannabis plants the same key principles apply. If growing in a grow medium such as soil, the cannabis roots need to be kept in the ‘goldilocks’ sweet spot where they are neither over-watered nor under-watered.

Those growing in hydroponics systems such as deep water culture (‘DWC’) won’t need to worry about over-watering. By definition, a good hydroponic grow system will have specialist attention given to deliberate oxygenation of the roots, perhaps with an air-stone or similar.

For anyone unfamiliar with the technically challenging array of hydroponic grow options and how best to use them the following in-depth guide is essential reading.

Cannabis stage-by-stage watering schedule

With so many different factors influencing the specific amount of water required by your plants it should be clear that watering your cannabis requires some skill if you are to grow your plant from cannabis seed to harvest without over-watering or under-watering. As your experience grows, your natural ability to gauge and assess water needs will improve. Weighing your plant container is one way to know how much water they contain.

A hygrometer is highly recommended to growers of all skill levels to know precisely how much moisture is available to the cannabis roots. The following guidelines may also help.

seeding watered outside how to water your cannabis plants blog Dutch Passion

Cannabis seeds and water

It may seem strange to consider the water needs of cannabis seeds. But one of the main causes of poor germination rates is due to weed seeds being germinated in excessively wet conditions. If left for too long in soaking conditions (e.g. several days submerged in water) the newly emerged tap root can rot and die.

After several decades supplying cannabis seeds, the Dutch Passion team feel that the best way to germinate cannabis seeds is between two lightly sprayed/dampened cotton wool pads.

Watering cannabis seedlings

Cannabis seedlings require less water than at any other stage of their growth cycle. Water usage is low. The tiny leaves have minimal water transpiration rates. When watering seedlings recognise that water requirements are small. Problems often come from over-watering seedlings in soil which leaves roots unable to grow and stunts the plants. Cannabis seedlings can also be damaged if battered by a strong flow of water from a great height.

Watering cannabis plants in there veg fase Dutch passion

Watering cannabis during the vegetative stage

Water usage rates gradually increase during vegetive growth. Plants produce more leaves which all transpire. The cannabis root system also gradually increases in size allowing the plant to gather more water and nutrients as it grows and prepares for eventual bloom.

watering cannabis plant during flowering fase Frisian Dew indoor greenhouse dutch passion

Watering cannabis during the flowering stage

Water requirements are highest during bloom. At this stage the plant has reached it’s maximum biomass. If you grew the best cannabis seeds you may have a large plant with numerous blooms and a tent-filling stature. Such plants can consume several litres of water/nutrients per day but will reward the attentive grower with heavy THC rich harvests.

Cannabis plants watering FAQ

semi hydro autopot xl system with clay pebbles and coco

Watering your cannabis plants and avoiding over-watering/under-watering is more complicated than it may initially sound. Many growers struggle with watering, often over-watering grow after grow.

As a result, they miss out on the best potency. But with a little practice and some useful tips (such as a hygrometer and/or weighing your grow containers to assess water needs) you will soon be able to overcome watering issues and see better plant growth as well as superior quality harvests.

The best watering frequency is that which delivers neither over-watering nor under-watering in your specific grow conditions. Many experienced growers will know the water needs of their plants in their grow system at various stages of growth.

A large 2-metre-tall indoor plant of a particular strain, grown in coco fibre may need several litres of water/nutrients per day. Some growers prefer to deliver this liquid in several instalments throughout the day to avoid excessive drying out.

However, this may not be practical for every grower who may just be able to water their plants once per day. The key principle is to ensure that your plants never dry out, nor should they be overwatered.

An automatic watering system that continuously drips nutrients is preferred by some people. Others would opt for something like the AutoPot system that gravity-feeds nutrients only when the grow medium has partially dried out. Cannabis will grow well with either approach and there are numerous different grow systems with varying approaches to watering and automation.

These involve techniques such as flood and drain, drip feeding, timer-based watering systems and many others. Remember that the cannabis plant needs to avoid the stressful extremes of having permanently waterlogged roots as well as avoiding the near-death experience of wilting and drying out.

When grown organically in soil, which naturally buffers pH, the pH of your incoming water supply is rarely an issue and many soil growers never check water pH. Connoisseur soil growers may choose to adjust pH to the soil-preferred pH range of 6.3-6.8. But most soil growers don’t bother.

Those growing with other grow methods/grow mediums (e.g. coco or hydroponic growers) may well have to control water/nutrient pH nearer 5.6-5.8 to ensure that all minerals are bio-available to the cannabis roots.

Cannabis nutrient lockout occurs if the wrong pH is used. With nutrient lockout, even if minerals are present, they cannot be absorbed if the pH is outside preferred limits.

the importance of good drainage and avoid run off water

If growing in e.g. soil, coco fibre (or similar) check to see that water/nutrients run freely through your grow medium and collect in a pool of run-off at the bottom of your container within a minute or two.

If you see slow run off, it could be due to poor drainage. This can happen if the e.g. soil blend is too heavy. Addition of perlite, coco fibre or light mix soils could be methods of improving drainage.

Some people collect the run-off water in a saucer or tray underneath their plant containers. This can be drained away by gravity or pumped away. If you have just a few plants you may find it easiest to pour the run-off away or ‘mop’ it up with a sponge by hand. Run-off water can contain minerals in the wrong concentrations/ratios for growth and is typically discarded. Stale run off is a potential breeding ground for pests, mold and bacteria and has no place in your grow room. Get rid of it quickly.

Many growers actively avoid planning a vacation, even a short one, while they are growing. Others will arrange a friend to take care of their crop.

Many find it difficult finding someone they can trust to care for their crop and rely on automated watering devices, such as Wilma or AutoPot systems, to water their plants while away.

Use of large grow sacks is another option for soil growers. If using a large (e.g. 75 litre) grow sack of soil a small cannabis plant may be able to survive a week or so without needing additional watering.

However, larger cannabis plants will be less forgiving and will have greater water needs. Many grow shops sell specialist automatic watering devices, drip lines, pumps etc.

If you plan to be away from your plants regularly it pays to plan ahead and buy/design a system that meets your needs and time availability.

Another useful safety tip for anyone worried about leaving their plants alone is to get a temperature activated fire extinguisher for their grow room.

These automatically discharge if the grow room temperature exceeds a specified limit on the extinguisher. If growing with good quality equipment and legal electricity grow room fires are rarely heard of.

For the grower seeking maximum peace-of-mind while away from their plants, a temperature activated fire extinguisher may be useful.

Some growers that routinely grow in the same size containers in a stable grow environment manage to grow their plants well with little need for gadgets to assist them.

Many other growers, including expert-level cultivators prefer to use all the grow room monitoring tech that they can get. Many growers take their passion seriously!

Digital thermometers: A simple thermometer allows the grower to keep their plants at (or near) optimised temperatures. A digital thermometer can be connected to the fan/extraction system and automatically demand e.g. higher extraction/air-flow rates in hotter temperatures.

Hygrometer: A hygrometer measures the humidity of the air in your grow room. They are used by growers to track changes in humidity levels. The grower can then adapt their grow room accordingly with e.g. dehumidifiers. Hygrometers are often available as a combined thermometer/hygrometer, they are inexpensive and one of the most useful grow room tools for growers of all experience levels.

Tensiometer: Used to measure the surface tension of water with the grow medium, which in turn indicates the water moisture content. These are very popular with committed home growers and affordable enough to consider one for each plant. Even knowledgeable growers with years of experience still find tensiometers to be one of the most useful grow room gadgets and use them routinely.

pH Meter: These measure the level of acidity/alkalinity in a liquid, e.g. a nutrient feed solution. Soil/compost has a certain degree of pH self-buffering, meaning pH is less critical. But those growing in hydro or coco will need to accurately control nutrient pH. If pH is wrong, nutrient lockout can occur. This means that, even though the nutrients are available in the grow medium, they can’t be absorbed due to the pH being out of range. A pH of around 5.8 is often used by hydro/coco growers.

EC/TDS Meters: An EC (Electrical Conductivity) meter or a TDS (Total Dissolved Solids) meter determine the amount of dissolved minerals in your nutrient feed solution. These help growers to ensure stable feeding regimes and avoid the dangers of over/under feeding.

Watering cans with measurements: Rather than pour imprecise volumes of water/feed solutions from a watering can, many prefer to use a watering can with accurate dispensing. Some watering cans are made from a transparent material with a clear scale showing the grower exactly how much water has been poured. For any grower that has struggled with over/under watering these watering cans allow accurate water/nutrient doses to be made.

Runoff Trays: Run-off trays allow the excess water that runs from the bottom your plant containers to be collected. This is often pumped away to waste or mopped up with a sponge. The logic is simply to prevent the plant containers from sitting in run-off water. Cannabis roots prefer aerated conditions to waterlogged conditions. Leaving stale, stagnant water in your grow room is risky due to pests and diseases.

Run-off water contains an unknown mix of nutrients that trickles out of the container. For this reason, it is rarely re-used. Logically it’s better to feed your plants with freshly prepared nutrients of optimum composition rather than waste runoff water.