Watering cannabis plants is crucial for growth, but there is no fixed schedule. Frequency depends entirely on the plant’s size, the growing environment, and the type of medium used. Successful cultivation relies on checking the moisture levels of the growing medium and providing water only when the plant is ready. This tailored approach prevents roots from suffocating in overly wet conditions or suffering from dehydration.
How to Determine When Your Plants Need Water
The decision to water should always be based on the dryness of the growing medium, which can be assessed using a few reliable methods. A common technique is the “knuckle test,” where you insert a finger about one to two inches deep into the soil. If the medium feels dry at that depth, it is typically time to water the plant again; if it still feels damp, you should wait another day or two.
Many experienced growers rely on the “lift test” to gauge the moisture level by the weight of the container. After a thorough watering, lift the pot to memorize the weight of a fully saturated medium. You should water the plant again when the pot feels significantly lighter, indicating that much of the water has been used or evaporated. This method provides a clear, physical cue that the plant has drawn sufficient moisture from the medium.
For a more objective measurement, you can use a soil moisture meter, which is a probe inserted into the medium to provide a numerical reading of the water content. This tool is particularly helpful for new growers to standardize their watering process. The goal is to allow the top layer of the medium to dry out completely between watering cycles, which encourages the roots to grow outward in search of moisture and ensures they have access to oxygen.
Watering Frequency Across the Cannabis Life Cycle
Seedlings and young clones require a very small amount of water, often needing only light and frequent applications to keep the medium moist but not saturated. Overwatering is a common mistake at this stage, as the small root system cannot absorb large volumes of water, risking root rot and fungal disease.
As the plant enters the vegetative stage, its root mass and canopy expand rapidly, leading to a significant increase in water usage. During this period, the frequency of watering will increase, often requiring a full watering every two to four days, depending on the environment. The plant’s high metabolic rate demands more water for transpiration and nutrient transport, but the principle of allowing the medium to dry slightly between waterings still applies.
In the flowering stage, mature plants with a large canopy and dense root system continue to have high water needs, often requiring water every two to three days. Some growers intentionally reduce water intake slightly during the final week or two before harvest, a technique believed by some to stress the plant and potentially increase resin production. Throughout the life cycle, the volume of water applied should be based on the plant’s current size, not the size of the container it is in.
Environmental and Medium Factors That Change Water Use
Beyond the plant’s growth stage, external factors and the properties of the growing medium heavily influence how quickly water is used and how often it needs to be replenished. Higher temperatures accelerate transpiration, the process of water movement and evaporation from the plant and medium surface. Conversely, lower humidity means the plant loses water more slowly and will need less frequent watering.
The physical structure of the growing medium is also a primary factor in water retention. Soil-based mediums tend to hold moisture longer and require less frequent watering than soilless mediums like coco coir. Coco coir, for example, is highly porous and drains quickly, often necessitating more frequent watering, sometimes even daily, but it should never be allowed to dry out completely.
Container size dictates the volume of water held; smaller pots dry out much faster than larger pots. Fabric pots also affect water use; they promote air pruning of the roots and allow for greater oxygen exchange, which leads to faster evaporation from the sides.
The Technique of Proper Watering
You should water slowly and evenly across the entire surface of the medium, not just at the base of the stem. Watering around the stem is discouraged because it can encourage stem rot and prevents the entire root ball from being saturated.
The goal of a proper watering is to fully saturate the medium until 10% to 20% of the water drains out the bottom of the container, known as runoff. This runoff flushes out accumulated mineral salts and prevents nutrient buildup in the root zone, which can lead to nutrient lockout. Without sufficient runoff, these salts can concentrate and cause toxicity.
The water or nutrient solution applied must be within the correct pH range to ensure the plant can absorb nutrients effectively. For soil growers, the ideal pH range is generally between 6.0 and 7.0, while soilless mediums like coco coir or hydroponics require a slightly lower pH of 5.5 to 6.5. If the pH is too far outside this range, specific nutrients become chemically unavailable to the plant.
Identifying Symptoms of Incorrect Watering
Underwatering causes the plant to wilt, with leaves drooping and feeling limp, flimsy, and sometimes brittle or dry to the touch. The medium will also appear significantly dry, and the pot will feel very light, which confirms the issue.
In contrast, overwatering is characterized by drooping leaves that often still feel firm or turgid, a result of the roots being deprived of oxygen in the saturated medium. The medium will be heavy and soggy, and the roots will begin to suffocate, leading to a breakdown in function. Overwatering can also cause yellowing of the lower leaves, a symptom often mistaken for a nutrient deficiency, but the root cause is the lack of oxygen preventing nutrient uptake.