Watering cannabis plants is where new growers often encounter problems, as both overwatering and underwatering severely inhibit growth. Water acts as the vehicle for nutrient delivery and is essential for photosynthesis, making proper management a primary determinant of a plant’s health and final yield. The goal is to maintain a healthy balance, allowing roots access to both moisture and oxygen by letting the growing medium partially dry out between applications. This practice encourages a more extensive root system as the plant seeks moisture. A static watering schedule is ineffective because consumption changes daily based on the plant’s size and environment.
Determining When to Water
The frequency of watering should be dictated by the plant’s current moisture needs, not by a fixed calendar schedule. A simple and reliable method is the “lift test,” which involves lifting the container after a thorough watering and noting its weight. When the pot feels significantly lighter, approximately 50% of the initial saturated weight, it signals that a substantial amount of water has been consumed or evaporated, indicating it is time to re-water.
A physical check, often called the “knuckle test,” can also be used to assess the moisture level of the upper substrate layer. By inserting a finger one to two inches deep into the medium, a grower can determine if the top layer is dry enough. If the substrate feels dry at that depth, the plant is likely ready for water. This manual check helps confirm the lift test, ensuring the plant is not sitting in waterlogged conditions.
Allowing the medium to partially dry out between waterings is a deliberate strategy to promote root health. This “dry-back cycle” ensures the root zone receives necessary aeration, preventing root suffocation and encouraging the roots to stretch out in search of moisture. Consistent monitoring of the medium’s moisture status is far more effective than adhering to a rigid timeline.
The Mechanics of Proper Application
When watering, the application technique is as important as the timing to ensure the entire root ball is saturated evenly. Water should be applied slowly and deliberately, distributing it across the entire surface of the growing medium, not just at the base of the main stem. This slow application prevents the water from carving channels through the soil, which leads to dry pockets and uneven hydration.
The application volume should be sufficient to produce a measurable amount of runoff from the bottom of the container. Aim for a volume that results in 10–20% of the applied water draining out. For example, if a plant receives one gallon of water, about one-fifth of a gallon should exit the pot.
This runoff serves the purpose of flushing out excess mineral salts that accumulate in the root zone from previous nutrient applications. Allowing these salts to build up can lead to nutrient imbalances and “nutrient lockout,” where the plant is unable to absorb available elements. It is important to promptly remove this excess runoff water from the collection saucer so the plant does not reabsorb the flushed salts.
Water Quality and Preparation
The quality of the water used directly impacts nutrient availability and overall plant health. The most important parameter to measure and adjust is the pH level, as this controls which nutrients the plant can absorb. For cannabis grown in soil, the ideal pH range is between 6.0 and 7.0, while soilless mediums like coco coir or hydroponics require a slightly more acidic range of 5.5 to 6.5.
If the pH of the water is too high or too low, certain elements become chemically unavailable to the plant roots, leading to deficiencies. Growers must use pH Up or pH Down solutions to adjust the water’s acidity or alkalinity to the appropriate range after any nutrients have been mixed in. Checking the pH of the runoff water also provides insight into the chemical conditions within the root zone.
Another factor to consider is the concentration of dissolved minerals and salts, measured as Total Dissolved Solids (TDS) or Electrical Conductivity (EC). When mixing nutrient solutions, the initial EC/TDS of the source water must be accounted for to prevent over-fertilization. If using municipal tap water treated with chlorine or chloramines, which can harm beneficial soil microbes, let the water sit in an open container for 24 hours to allow the chlorine to dissipate before use.
Adjusting Watering for Growth Stages
A plant’s water requirements change dramatically throughout its lifecycle, necessitating continuous adjustment of both the volume and frequency of watering.
Seedling and Clone Stage
In the seedling and clone stage, root systems are underdeveloped and fragile, requiring very small amounts of water applied frequently. The goal is to keep the immediate root zone moist but not saturated, often by misting or applying water in a small ring around the stem to encourage root exploration.
Vegetative Stage
As the plant transitions into the vegetative stage, its size and metabolism increase rapidly, demanding a corresponding increase in water volume. The root system expands to fill the container, and the plant needs a full saturation watering that results in runoff. The frequency of watering slows down compared to the seedling stage, as the larger volume of water takes longer to be consumed and for the medium to achieve dry-back.
Flowering Stage
During the flowering stage, water consumption peaks as the plant focuses energy on bud production and transpiration rates are high. Watering volume remains high, ensuring full saturation to support the large root mass. In the final one to two weeks before harvest, many growers slightly reduce the water volume and cease nutrient application, a process known as flushing. Proper saturation and runoff mechanics should still be maintained until the final days.