How Much Water Do Weed Plants Need

By: Maria

Home > Grow > How Much Water Do Weed Plants Need

This website is intended for entertainment purposes only. Always consult with a qualified medical professional or legal advisor before making any decisions based on its content.

Plants can’t tell us what they need, especially cannabis. So, how much water is the right amount? 

Starting to grow cannabis and have your seeds ready? You might be wondering, “how much water do weed plants need?” Can you give your plants too much water? What type of water should you use? And what’s the best way to water them?

Don’t worry! We’ve made this guide to help you water your cannabis plants the right way.

How Much Water Do Weed Plants Need?

The answer isn’t as straightforward as you might think. Cannabis plants, like all living things, need water to survive. However, the amount of water they need can vary based on several factors, including the plant’s size, the stage of growth, and the environment. A general rule of thumb is to water until you see about 20% runoff from the bottom of the pot. But remember, it’s better to underwater than overwater.

1. The Plant’s Lifecycle:

Cannabis plants have different water requirements depending on their stage of growth. For instance:

  • Seedlings: These baby plants have tiny root systems and can’t handle a lot of water. They prefer a moist environment, but not a waterlogged one.
  • Vegetative Stage: As the plant grows and its root system expands, it will require more water. However, it’s essential to ensure that the soil doesn’t remain wet for extended periods.
  • Flowering Stage: During this crucial phase, the plant’s water requirement can increase, especially as buds form and mature.

2. Size of the Plant:  

A small plant with a limited root system will require less water than a large, mature plant with an extensive root system. As the plant grows, its ability to uptake and utilize water increases.

3. Type of Growing Medium:  

Different growing mediums retain water differently. For instance:

  • Soil: Retains water well and provides a buffer against overwatering. However, it can become compacted, which may restrict root growth and water uptake.
  • Coco Coir: This medium retains moisture but also allows for good drainage, making it harder to overwater.
  • Hydroponics: Plants grown in water-based systems have constant access to water, but the system’s design ensures they also get enough oxygen.

4. Environmental Factors:

The environment in which you’re growing plays a significant role in water requirements.

  • Temperature: On hot days, plants will transpire more, leading to increased water uptake. Conversely, on cooler days, they’ll need less.
  • Humidity: In high humidity, plants might not transpire as efficiently, leading to reduced water uptake. In low humidity, they might need more frequent watering.

5. Pot Size and Type:

The container’s size can dictate how quickly the medium dries out. A small pot dries out faster than a large one. Additionally, fabric pots or “air pots” can allow for better drainage and prevent overwatering.

6. The 20% Runoff Rule:  

Watering until you see about 20% runoff from the bottom of the pot ensures that the entire root zone is moistened. This runoff also helps flush out any excess salts or nutrients that might accumulate in the soil, preventing potential root damage.

7. The Underwatering Principle:  

While it might seem counterintuitive, it’s often better to err on the side of underwatering than overwatering. Overwatering can lead to root rot, a condition where the roots are deprived of oxygen, become weak, and susceptible to diseases. Underwatered plants, on the other hand, can usually recover quickly once they’re given a good drink.

When’s the Best Time to Water Cannabis?

Timing is everything, even when watering cannabis. The best time to water your plants is in the early morning, just as the lights come on. This allows the water to be absorbed throughout the day, preventing the growth of mold and other fungi that thrive in damp, dark conditions.

What’s the Best Way to Water Cannabis? 

Watering is a fundamental aspect of cannabis cultivation, and the method you choose can significantly impact your plant’s health and yield. Let’s delve deeper into how to water canabis and look at the various watering techniques available

1. Spraying: 

What is it?  

Spraying involves misting water onto the soil or growing medium using a spray bottle or mister. It’s Ideal for seedlings and young plants. It allows for gentle watering, reducing the risk of overwatering.


  • Gentle on Young Plants: Spraying is incredibly gentle, making it perfect for seedlings and young plants that have delicate root systems.
  • Controlled Moisture: It allows for controlled moisture levels, ensuring the soil is damp but not waterlogged.
  • Prevents Soil Disruption: The gentle nature of spraying means the soil isn’t disturbed, protecting young roots.


  • Not Suitable for Mature Plants: As plants grow, their water needs increase, making spraying an inefficient method for mature plants.
  • Time-Consuming: If you have many seedlings, spraying each one can be time-consuming.

2. Manual Watering:  

What is it?  

This is the most common method. It gives you control over how much water each plant receives, but it can be time-consuming. Manual watering involves pouring water directly onto the soil or growing medium, typically using a watering can or hose. 


  • Precision: You have complete control over the amount of water each plant receives.
  • Flexibility: Allows you to adjust the watering amount based on each plant’s specific needs.
  • Direct Root Zone Watering: Ensures that water reaches the root zone, promoting healthy root growth.


  • Time-Consuming: Especially in larger gardens, watering each plant can be a lengthy process.
  • Risk of Overwatering: Without careful attention, it’s easy to give plants more water than they need, leading to potential issues like root rot.

3. Drip Irrigation:  

What is it?  

Drip irrigation is a system where water is delivered directly to the plant’s root zone through a network of tubes, pipes, and emitters. It’s commonly used in large-scale agriculture and is becoming increasingly popular among cannabis growers. It’s a more advanced method. It ensures each plant gets the exact amount of water it needs, saving you time and effort.


  • Efficiency: Delivers water directly to where it’s needed, reducing water wastage.
  • Consistent Watering: Ensures each plant receives a consistent amount of water, promoting even growth across your garden.
  • Time-Saving: Once set up, the system automates the watering process, freeing up your time.
  • Reduced Risk of Diseases: By keeping foliage dry, drip irrigation reduces the risk of fungal diseases.


  • Initial Setup: Setting up a drip irrigation system can be complex and might require some initial investment.
  • Maintenance: The system can get clogged or damaged, requiring regular checks and maintenance.

How Often To Water?

After figuring out “how much water weed plants need,” the next logical question is, “how often?” Many growers swear by the method of checking the soil’s dryness. If the top 5cm of soil is dry, it’s time for a drink. Depending on your environment, this could mean daily watering or every few days.

How to Tell if a Cannabis Plant Needs Watering

Your plants will give you signs when they’re thirsty. Look for drooping leaves, dry soil, and slow growth. A simple trick is to lift the pot. If it feels light, it’s time to water.

  • Drooping Plants: A clear sign of thirst. But be careful; overwatered plants can also droop but will appear darker and more “heavy.”
  • Yellow or Brown Leaves: Discolored leaves can indicate a thirsty plant.
  • Check the Soil: The simplest method? Stick your finger in the soil. If the top 5cm feels dry, it’s time to water.

Ensuring the Right Water Quality for Cannabis

Cannabis plants prefer slightly acidic water, with a pH between 6.0 and 7.0. Using filtered or distilled water can help maintain the right pH balance and prevent the buildup of harmful minerals.

How to Flush Weed Plants

Flushing cannabis plants is a crucial step in the cultivation process, especially as you approach harvest time. But what exactly is flushing, and why is it so important? Let’s dive in.

What is Flushing?

Flushing cannabis involves running pure water through the soil or medium to wash away any leftover nutrients. This process ensures that the plants use up any remaining nutrients in their system, leading to a cleaner, smoother final product.

Why Flush? 

1. Improved Taste and Smoothness: Excess nutrients can affect the taste of the final product, making it harsher when smoked. Flushing cannabis helps in getting rid of these nutrients, resulting in a smoother and better-tasting bud.

2. Prevents Nutrient Lockout: Over time, nutrient salts can build up in the soil, leading to nutrient lockout where plants can’t absorb what they need. Flushing helps reset the soil, preventing this issue.

3. Healthier Plants: Flushing cannabis can help if your plants show signs of nutrient burn or other nutrient-related issues, giving them a fresh start.

How to Flush Weed Plants:

1. Choose the Right Time: The best time to flush is a week or two before you plan to harvest. If you’re flushing due to nutrient issues, do it as soon as you notice the problem.

2. Use Clean Water: Ensure the water you use for flushing is clean and free of contaminants. If possible, use distilled or reverse osmosis water. The pH should be balanced to the preference of cannabis, typically between 6.0 and 7.0.

3. Flush Thoroughly:  

   – Soil: Water the plants as you usually would, but without adding any nutrients. Continue watering until you see runoff from the bottom. Repeat this process 2-3 times to ensure all nutrients are washed out.

   – Hydroponics: Replace the nutrient solution with pure, pH-balanced water for several days.

   – Coco Coir: Like soil, run clean, pH-balanced water through the medium until you see runoff. Repeat a couple of times.

4. Monitor Your Plants: After flushing, keep a close eye on your plants. They might show signs of nutrient deficiency as they use up the last of their internal reserves. This is normal, especially if you’re close to harvest.

5. Resume Normal Watering: If you’re not close to harvest, after flushing cannabis, you can resume your regular watering and feeding schedule, but be cautious. Start with a reduced nutrient dose and adjust based on your plant’s response.

How to Collect Water Runoff

Collecting runoff is crucial to prevent overwatering. Place a tray under your pots to collect excess water. If the tray fills up quickly, you’re likely overwatering.

Symptoms of Underwatering Cannabis and How to Solve Them

Underwatered cannabis plants may have drooping, yellow leaves and stunted growth. If you notice these signs, increase your watering frequency. But do it gradually to avoid shocking the plant.

Symptoms of Overwatering Cannabis and How to Solve Them

Overwatered plants also have drooping leaves, but they’ll feel wet and look darker. The plant may also show signs of nutrient deficiencies. If you’re overwatering, reduce your watering frequency and ensure your pots have good drainage.


It’s important to ask “how much water do weed plants need” because it is a crucial part of cannabis cultivation. It requires a keen eye and a willingness to adapt to your plants’ needs. But with patience and practice, you’ll master how to water canabis, leading to healthier, happier plants. Happy growing!

Leave a Comment