Watering is frequently the most challenging aspect of successful cannabis cultivation and the most common mistake made by new growers. There is no fixed schedule for watering a weed plant because its needs change constantly based on size and environment. Instead of relying on a calendar, growers must follow principles centered on the “wet/dry cycle” to ensure the roots receive both water and necessary oxygen. Understanding when and how much water to apply separates a healthy plant from a struggling one.
Determining the Ideal Watering Time
The core principle of watering is maintaining a healthy wet/dry cycle, which promotes robust root development and prevents oxygen deprivation. When the growing medium is saturated, roots absorb water and nutrients, but they need a period of “dry back” to breathe. If the medium remains saturated too long, the roots essentially drown, leading to issues often mistaken for nutrient deficiency. This cycle ensures the root zone remains aerobic.
The most reliable method for determining when to water is the “Lift Test,” which involves monitoring the container’s weight. Immediately after a thorough watering, lift the pot to establish the “wet weight” baseline. When the pot feels noticeably light—about 50% to 75% lighter than the saturated weight—it signals that moisture has been consumed, and it is time to re-water. A secondary method is the “Knuckle Test,” where inserting a finger two inches deep into the medium determines if the soil is dry enough.
When it is time to water, the goal is to fully saturate the entire root zone, achieved by applying enough water to result in 10% to 20% runoff from the container bottom. This intentional runoff flushes out accumulated mineral salts and excess nutrients that can build up in the medium, preventing nutrient lock-out. If using nutrients, the runoff ensures the roots receive a balanced solution. Always remove the runoff water promptly, as allowing the pot to sit in it defeats the purpose of the dry-back cycle and can lead to overwatering.
Adjusting Watering Frequency by Growth Stage
The frequency of watering is directly tied to the plant’s size and its rate of transpiration, which changes dramatically throughout its life cycle. Seedlings and clones have small, undeveloped root systems, making them highly susceptible to overwatering. For these young plants, focus on small, targeted applications of water near the stem base, often just a few hundred milliliters, to avoid completely saturating the pot.
As the plant enters the vegetative phase, its growth accelerates significantly, and its root mass expands to fill the container. During this stage, water uptake increases rapidly, and watering frequency will likely increase to every two to four days, depending on the pot size and environment. The increased transpiration rate means the medium dries out faster, allowing the grower to deliver fresh nutrients more often.
The flowering phase marks the period of peak water consumption, as the plant supports the massive growth of buds and foliage. Mature plants in full bloom may require watering every other day, or sometimes daily in high-heat or low-humidity environments. A common technique involves slightly reducing the volume and frequency of water application in the final week or two before harvest, often called “flushing.”
How Medium and Environment Influence Scheduling
The type of growing medium drastically affects how often a plant requires water because different materials retain moisture for varying lengths of time. Traditional potting soil acts like a sponge, holding water longer, often necessitating watering only every three to five days. This medium naturally provides a longer interval between watering events, making it more forgiving for beginners.
In contrast, inert, soilless media like coco coir or rockwool have excellent aeration and drainage, meaning they hold less water and dry out more quickly. Plants in coco coir often require daily watering, and sometimes multiple times per day in advanced setups, because the medium is intended to be fed almost constantly. This frequent feeding schedule is necessary because coco coir has a low cation exchange capacity and does not retain nutrients well.
Container size is another physical factor that directly influences the watering timeline, as a larger volume of medium retains moisture longer. A plant in a small one-gallon pot will dry out much faster than the same plant in a five-gallon container, requiring a shorter interval between waterings. Environmental factors also play a large role: high temperatures increase the plant’s transpiration rate, causing it to “drink” more and the medium to evaporate moisture faster. Low humidity accelerates water loss from the leaves, meaning a plant in a hot, dry environment needs water more frequently than one in a cooler space.
Diagnosing and Correcting Watering Problems
Two main issues arise from improper watering: overwatering and underwatering, though their symptoms can often look similar. Overwatering is typically the result of watering too frequently, which starves the roots of oxygen and leads to root problems. The primary symptom is a general drooping of the leaves, which feel firm and swollen because the plant cells are engorged with water.
The leaves of an overwatered plant may also begin to yellow, and overall growth will slow dramatically as the root system struggles. The immediate correction for overwatering is to stop applying water completely and allow the medium to dry out thoroughly until the pot is significantly light again. This recovery period may take several days, but it is necessary to restore oxygen to the root zone and prevent root rot.
Conversely, underwatering is characterized by leaves that droop and feel thin, limp, and brittle, indicating a loss of turgor pressure. The container will feel extremely light, and the medium may visibly pull away from the sides of the pot. While underwatering causes stress, it is easily corrected by slowly applying a thorough saturation of water until 10% to 20% runoff is achieved, allowing plants to recover rapidly within a few hours.