Feeding a cannabis plant is a dynamic management system that changes based on the plant’s life stage and the growing medium. Providing the correct concentration of nutrients at the right time is paramount for maximizing plant health and final yield. An effective feeding regimen requires understanding the plant’s evolving nutritional demands and monitoring the environment for optimal uptake.
Nutrient Requirements by Growth Stage
The nutritional needs of a cannabis plant shift significantly throughout its lifecycle, requiring a proportional change in the nutrients provided. The three primary macronutrients are Nitrogen (N), Phosphorus (P), and Potassium (K). These elements fuel different aspects of growth, and the NPK ratio must be adjusted for each phase.
During the initial seedling phase, the young plant requires minimal external feeding, often relying on the stored energy within the seed. Once the first true leaves emerge, a very light nutrient solution, around 200–400 parts per million (PPM), is introduced to encourage root establishment. This early feeding prevents nutrient burn on the delicate new growth.
The Vegetative phase is characterized by explosive growth of leaves and stems, demanding high amounts of Nitrogen. Nitrogen is essential for producing chlorophyll and driving photosynthesis, so the ideal NPK ratio during this period is high in the first number, often around 3:1:2 or 3:1:1. This N-rich diet builds the robust structural support necessary to bear the weight of later flower production.
When the plant transitions into the Flowering phase, its focus shifts entirely to producing buds. Nitrogen should be significantly reduced to avoid delaying flower development, while Phosphorus and Potassium intake must increase dramatically. An NPK ratio of approximately 1:3:2 is common during early to mid-flower to support energy transfer and bud formation.
In the final weeks before harvest, the plant enters a Ripening phase, where nutrient application is temporarily stopped in a process called flushing. This involves feeding the plant only clean, pH-balanced water to encourage it to consume its stored nutrients and residual salts. Flushing, typically lasting one to two weeks, is done to enhance the final product’s flavor and smoothness.
Determining Feeding Frequency Based on Growing Medium
The frequency of nutrient application is directly dictated by the chosen growing medium. Soil acts as a natural buffer, holding onto nutrients and releasing them slowly to the plant’s roots. This buffering capacity means soil-grown plants require less frequent feeding, generally following a “Feed/Water/Water” or “Feed/Water/Feed” cycle.
For soil, a typical schedule involves feeding once every five to seven days, depending on the plant’s size and consumption rate. The space between feedings allows the soil to dry out, which is necessary to pull fresh oxygen into the root zone and prevent the roots from suffocating. A grower should wait until the top inch of soil feels dry or the pot feels noticeably light before re-watering.
In contrast, soilless media like coco coir or inert hydroponic systems have almost no nutrient-holding capacity. In these setups, nutrients must be delivered constantly or with nearly every watering in a technique called high-frequency fertigation. For coco coir, feeding is often required at least once a day, and sometimes multiple times a day as the plant matures.
Every time a soilless medium is irrigated, a significant amount of nutrient solution must be applied to create runoff, typically 10–20% of the volume given. This runoff is essential for washing away accumulated mineral salts that can build up around the roots, preventing them from absorbing new nutrients. Hydroponic systems provide a continuous nutrient supply, but the reservoir solution must be monitored and refreshed, often on a weekly basis, to ensure stable concentration and pH.
Monitoring for Optimal Nutrient Uptake
Continuous monitoring is essential to ensure the plant is properly utilizing the provided nutrients and is not experiencing toxicity or deficiency. Two primary tools used for this management are the pH meter and the Electrical Conductivity (EC) or Parts Per Million (PPM) meter.
The pH level is a measurement of acidity or alkalinity and is paramount because it directly controls nutrient availability. If the water’s pH is too high or too low, the plant’s roots cannot absorb certain elements, leading to nutrient lockout. Soil growers aim for a feeding pH between 6.0 and 7.0. Those using soilless or hydroponic media need a slightly more acidic range, typically 5.5 to 6.5.
The EC or PPM meter measures the total concentration of dissolved mineral salts. Growers measure the solution before feeding (input EC/PPM) and after it drains through the medium (runoff EC/PPM). If the runoff reading is significantly higher than the input, it signals a salt buildup in the root zone, indicating the feed strength should be lowered or a flush is needed.
Visual cues from the plant also provide immediate feedback on the feeding program’s effectiveness. Signs of overfeeding, known as nutrient burn, appear first as yellow or brown tips on the leaves. This can sometimes progress to a downward curling called “clawing,” especially if Nitrogen is too high. Conversely, underfeeding or nutrient lockout causes deficiencies, such as yellowing leaves starting from the bottom of the plant (Nitrogen deficiency) or yellowing between the veins (Magnesium deficiency), signaling the need for stronger or better-pH-adjusted nutrients.