Marijuana plants, like all living things, need water to survive. Water performs a host of functions, including aiding in nutrient uptake, maintaining cell turgidity, and much more. Yet ironically, it is one of the greatest threats to cannabis as well. Overwatering is one of the most common mistakes that growers make and one that can create many problems in the garden. So, in this article, we’ll provide an in-depth look at how to water cannabis plants.
How Much Water Do Cannabis Plants Need?
One of the most important things to consider when growing cannabis is how much water to give the plants. With some experience and education, you can estimate how much water to give them; however, it is very difficult to calculate a precise amount because there are many factors to consider. Some of these aspects include:
Stage of Growth
When the plants are small, you may need to water them only once every few days. But when they enter the vegetative growth period, they will start to uptake more water and nutrients, requiring you to either increase the pot size or water them more frequently.
Overall Health of the Plant
The health of your plants will determine how quickly they grow, how much they yield, and how much water they take in. Sickly plants with nutrient imbalances, diseases, or pest infestations may become stunted, requiring less water than they otherwise would need. If you notice that your plant’s growth has stalled, be careful not to worsen the problem by overwatering it.
Type of Strain
Cannabis has adapted to a wide range of environments, from arid mountains to tropical rainforests. As a result, different strains will have different needs regarding water, light intensity, temperature, and other environmental conditions.
Typically, Sativa varieties that hail from humid areas need more water than Indicas from Middle Eastern deserts. Research the strain you are growing and try to mimic the environment in which it has adapted to flourish.
Container Size and Type
The size of your containers is another key factor in how often you’ll need to water your plants. A large plant in a small container may need to be watered multiple times per day. Conversely, a small plant in a large container may only need to be watered once a week.
It’s a good idea to repot your plants as they grow rather than placing them in large containers from the start. This is because it is easy to overwater your plants accidentally if they are in oversized pots. The general rule of thumb is to provide 5 gallons of container space for every 12 inches of growth.
The type of container also can play a role in how quickly the medium dries out. Fabric pots have become widely popular because they help to prevent plants from becoming rootbound; however, they also dry out much more rapidly than traditional plastic or ceramic pots.
Many options are available when it comes to growing media, and each provides varying levels of moisture retention and drainage. A light, fluffy medium such as coco coir offers excellent drainage, so water and oxygen will move through it quickly. As a result, you’ll need to water more frequently than you would with typical potting soil.
Temperature and Humidity
Temperature and humidity are significant factors in the transpiration rate of plants. The higher the temperature, the faster plants transport water through their roots and leaves. And the higher the humidity, the slower plants will transpire.
Dialing in your temperature and humidity levels will allow you to water less frequently while boosting the growth of your plants. The best way to do so is to calculate your garden’s vapor pressure deficit (VPD).
How To Tell When Cannabis Plants Need Water
As you can see, many factors combine to determine how much water your plants need. Therefore, rather than attempting to create a formula for watering, it’s best to learn to read your plants and determine when they need a drink.
Wilted Leaves and Drooping Stems
The most apparent sign that plants need water is when the leaves and stems droop. This happens because plant cells require water to maintain their turgor. When there isn’t enough hydrostatic pressure in the cell, the plasma membrane collapses, and the plant tissue becomes soft and droopy.
It’s best to water your plants before they show signs of wilting. By the time the leaves start drooping, some damage has likely already been done to the plant tissues. Therefore, don’t rely on this indicator to determine when to water your plants.
Another thing to keep in mind is that plants may droop because you gave them too much water. Overwatering presents similar symptoms to underwatering, but an experienced grower can spot the differences. Typically, an overwatered plant will have rigid, dark-green leaves that may claw downward. Conversely, an underwatered plant will usually have soft, light-green leaves that are very delicate.
Brown or Yellow Leaves
Plant tissues will become necrotic if they aren’t supplied with water. Therefore, leaves may start to die and fall off the plant when underwatering is left unchecked. Additionally, because water transports nutrients throughout the plant, you may see signs of nitrogen, phosphorous, or potassium deficiencies if you aren’t providing enough moisture. So, before you increase the amount of fertilizer in your feeding regime, consider if you’re simply underwatering the plants.
Dry Soil and Lightweight Container
The best way to tell when your plants need water is to check the medium. Stick a finger into the top of the medium about half an inch deep to determine how damp it is. If the soil feels dry to the touch, the plant needs more water. If it feels moist, you’re good to go. And if it feels wet and soggy, you’ve probably overwatered your plant and will need to skip a watering.
Another easy way to gauge the moisture level of your plant is to judge the weight of the container. Water your plant and lift the pot to get a reference for how heavy it feels when adequately hydrated. If it feels lightweight the next time you pick it up, the plant probably needs some water. Once you practice this a few times, you’ll be able to give your plants just the right amount of water.
How To Water Cannabis Plants
Now that you understand how much moisture cannabis plants need how to tell when they’re thirsty, let’s dive into how to water them.
Check the pH
First, check the pH of your water before applying it to the plants. If you are growing in organic soil, this will be less of an issue than if you’re using a soilless medium. Still, using water that is wildly out of the correct pH range could harm the plants. The ideal pH range is typically between 5.5 and 6.5.
If you add any nutrients to the water, measure the pH after mixing in the nutrients. Some nutrients may raise the pH, and others may lower it, so always check after you’ve finished adding in all your nutrients.
Apply the Water
Next, apply the water evenly onto the surface of the medium, making sure not to leave any dry spots. A watering can will help disperse the water consistently throughout the medium.
Typically, the amount of water you’ll need to apply is approximately ¼ the volume of the pot. So, if you’re using a five-gallon pot, you may add up to 1.25 gallons of water. However, this depends on what medium and nutrients you are using.
If you’re growing in a soilless medium with synthetic fertilizers, you should aim to water until there is runoff in the tray at the bottom of the container. Conversely, if you’re using soil and organic inputs, avoid watering until runoff, as you’ll flush some fertilizers and beneficial microbes out of the medium.
Just remember, it’s better to slightly underwater a plant than to overwater it. So, when in doubt, go for a light watering and add more if needed.
Drain the Trays
After watering, drain the trays of any runoff. This will help to prevent anaerobic bacteria, fungi, and other pathogens from infecting the roots. You can use paper towels, large syringes, or a vacuum to drain the water from the trays. Another option is to use inclined trays that prevent the containers from sitting in the runoff.
If you’re using synthetic nutrients, it’s a good idea to check the pH and EC of your runoff at least a couple of times throughout the grow cycle. This will help you determine if your medium is correctly buffered and if you are giving your plants the right amount of nutrients.
Automatic Watering Systems for Cannabis
If you are away from the garden for extended periods or just don’t feel like hand watering your plants all the time, many automatic watering solutions are available. Some options are more effective than others but come with a higher price tag.
One popular method of watering is to use a drip irrigation system. These systems work by providing a small but continual stream of water to the root zone of the plants. When set up correctly, the trickle of water will keep the plants hydrated without drowning the roots. You can either use a high-tech drip line system with a pressure gauge and sensors or make a simple DIY drip system with a water bottle.
Another affordable option is to use self-watering stakes. Much like drip systems, these bulbs slowly release a small amount of water into the medium over time. Self-watering stakes work by creating a vacuum effect against the medium. When the soil dries out, air enters the stake and releases more water.
When Is the Best Time to Water Cannabis Plants?
Generally, it’s best to water plants when the temperature is cool, as they retain moisture better than during hot weather. In the summertime, watering during the early morning or evening will prevent the water from evaporating. During the cooler months, it’s best to water during the daytime, as the root zone might become too cold at night.
Those growing indoors in tents should avoid watering in the evening. When the tent is closed, the humidity level may rise substantially, creating a breeding ground for bud rot and other pathogens. If you need to water during the evening, leave the tent cracked and keep a fan blowing on the canopy.
What Type of Water Is Best for Cannabis Plants?
Water quality is an essential factor in plant health that growers often don’t consider. Just because water may be deemed safe for human consumption doesn’t mean it is ideal for your plants.
Unfiltered Tap Water
Tap water is the most convenient and affordable source for most growers; however, not all tap water is created equal. Some cities have very hard tap water with high levels of calcium, magnesium, sodium, and chlorine, while other water sources may be relatively low in contaminants.
High levels of contaminants may kill beneficial microbes in the soil or cause nutrient imbalances. Therefore, it’s a good idea to have your water tested before using it to grow cannabis.
Filtered Tap Water
If you find that your tap water is high in contaminants, you may need to invest in a filtration system. Many systems are available at various price points that can effectively purify the water. One of the most economical options is a Pur Faucet Mount Water Filter. This filtration system is relatively inexpensive and is sufficient for removing heavy metals and reducing chlorine in the water.
Another option is to use a reverse osmosis (RO) filter. These systems are typically more expensive than a simple faucet-mounted filter but are highly effective at removing contaminants in your water source.
It is important to note that if you use filtered water to hydrate your plants, you may need to add calcium, magnesium, and other micronutrients to the water or medium. Using RO water can leach the soil of trace minerals, leading to nutrient deficiencies in the plants.
Bottled water is usually an exceptionally pure water source that is great for small-scale gardens. While some brands can be pretty pricey, most stores have cheaper options available. The downside to using bottled water is that it isn’t an environmentally friendly solution. Many resources are needed to bottle and transport the water, and the bottles create a lot of plastic waste.
Rainwater and Greywater
Collecting rainwater or greywater with a water collection system is a free and effective way to hydrate your marijuana plants. These systems can be scaled to any size, and the water can be stored for long periods of time. Rainwater is also free of most harmful chemicals and contains higher levels of nitrogen and oxygen than tap water, which will aid in plant growth.
The downside is that some states have banned the collection of rainwater and greywater or have placed restrictions on how much water can be collected. If you plan on going this route, make sure to research your state and local laws on water collection.
Final Thoughts on How To Water Cannabis Plants
Understanding how and when to water cannabis plants is a skill that requires education and practice to master. You can follow every tip in this article, but you’ll still need a bit of trial and error to get it right. However, with a little patience and persistence, any grower can learn how to keep their plants healthy, happy, and hydrated.