Weed Crop Cultivation: From Seed to Harvest

The term “weed crop” refers to the cultivation of cannabis, a plant with a long history as an agricultural commodity used for fiber, food, and medicine. In the United States, its cultivation was once encouraged, with hemp being a required crop for farmers in the 17th century. The 20th century saw legal restrictions that led to a sharp decline in production, but a recent resurgence driven by changing laws and economic potential has repositioned cannabis as a significant agricultural product.

Cannabis Cultivation Environments

The choice of cultivation environment is a foundational decision for any cannabis grower. Indoor cultivation offers the highest degree of control over environmental variables like light, temperature, and humidity. This allows for consistent, high-quality products and the possibility of year-round harvests. This precision, however, comes at a high cost, requiring investment in equipment and high ongoing energy consumption, resulting in a larger carbon footprint.

Outdoor cultivation is the most traditional and cost-effective method, relying on natural sunlight and soil. This approach allows plants to reach their full genetic potential, often resulting in larger yields per plant. The main disadvantage is the lack of control over environmental factors, as plants are vulnerable to weather fluctuations, pests, and diseases. This can lead to variability in crop quality and limits cultivation to specific seasons.

Greenhouse cultivation represents a hybrid approach, combining benefits of both indoor and outdoor methods. By utilizing natural sunlight, greenhouses reduce energy costs compared to indoor setups while still offering protection from adverse weather and some pests. This environment allows for an extended growing season and greater control than open-field cultivation. While the initial investment is higher than for an outdoor grow, it is more cost-effective than a dedicated indoor facility.

Essential Growing Techniques for Cannabis

The success of a cannabis crop depends on several core cultivation techniques, starting with the choice of growing medium. Soil cultivation is common, as it acts as a natural buffer for nutrients and water. Soilless mediums like coco coir offer excellent aeration and drainage but require the grower to provide all nutrients. More advanced methods include hydroponics and aeroponics, which can lead to faster growth but demand precise management and are less forgiving of mistakes.

Lighting is another fundamental input, directly influencing plant growth. Indoor cultivators must use artificial lights, with options like high-intensity discharge (HID) and light-emitting diodes (LEDs) being common. LEDs are more energy-efficient, and broad-spectrum white light is often considered best for indoor growth as it mimics the sun. Light intensity, measured in micromoles, is a parameter that growers can increase to boost yields, but this must be done carefully to avoid stressing the plants.

Cannabis plants require a balance of macronutrients (nitrogen, phosphorus, potassium) and micronutrients. Nutrient needs change throughout the plant’s lifecycle, with higher nitrogen requirements during vegetative growth. The electrical conductivity (EC) of the nutrient solution is a measure of its concentration and must be managed alongside the pH, which should be kept in a slightly acidic range of 5.5 to 6.5 for optimal nutrient uptake. Irrigation strategies must be coordinated with light intensity, as higher light levels increase the plant’s demand for water and nutrients.

The Cannabis Plant Lifecycle and Harvesting

The cannabis plant progresses through four distinct lifecycle stages, beginning with germination. This phase starts when a seed absorbs water, activating metabolic processes that cause a taproot to emerge. The seed is then planted, and the first two small, round leaves, known as cotyledons, appear. These embryonic leaves provide the plant’s initial energy through photosynthesis.

Following germination is the seedling stage, which lasts for two to three weeks. During this period, the plant develops its first true leaves, which have the characteristic serrated edges. A healthy seedling is short with vibrant green leaves and begins to establish a robust root system. Careful attention to moisture is important, as the young plant is susceptible to disease in overly wet conditions.

The vegetative stage is a period of rapid growth where the plant develops its main stem, branches, and a full canopy of leaves. Lasting from three to fifteen weeks, this phase builds the structural foundation necessary to support future flowers. Growers provide 18 or more hours of light per day to encourage this growth. It is also during this stage that the plant’s sex can be determined; male plants are removed to prevent pollination.

The final stage is flowering, which is triggered by a change in the light cycle to 12 hours of light and 12 hours of darkness for photoperiod strains. This phase, lasting seven to fourteen weeks, is when unpollinated female plants produce resinous buds. Growers identify harvest readiness by observing visual cues. The pistils will darken from white to orange or brown, and the trichomes on the flowers will change from clear to a milky white.

Post-Harvest Processing of Cannabis

Once harvested, cannabis undergoes processing steps that influence the final product’s quality. The first step is trimming, which involves removing the larger fan leaves and smaller “sugar” leaves from the flowers. This can be done either before drying (wet trimming) or after (dry trimming). Wet trimming is often faster, while dry trimming is thought to better preserve the flower’s terpenes and delicate trichomes.

The next stage is drying, where the trimmed flowers are placed in a controlled environment to remove most of their moisture. Freshly harvested cannabis contains about 75-80% water, which needs to be reduced for proper preservation. The ideal drying conditions are a dark room with temperatures between 16–21°C and relative humidity around 50–60%. This slow process helps to break down chlorophyll, eliminating a harsh, vegetal taste.

After drying, the flowers are moved into airtight containers for curing, a process lasting from two weeks to several months. During this time, the containers are periodically opened, or “burped,” to release built-up gases and introduce fresh air. This step allows the chemical profile of the flowers to fully develop, enhancing flavor, aroma, and overall quality while ensuring long-term shelf stability.

Cultivating Different Cannabis Varieties

Cultivation strategies often need to be adapted based on the specific variety of cannabis being grown and its intended end use. Legally, cannabis with less than 0.3% THC is classified as hemp. Though biologically the same species, the cultivation goals for high-THC cannabis, high-CBD cannabis, and industrial hemp lead to different agricultural practices.

For example, plants cultivated for high-THC or high-CBD flowers are grown with significant space between them to encourage bushy growth and maximize flower production. In contrast, industrial hemp grown for fiber is planted very densely to encourage the growth of long, tall stalks with minimal branching. This method can see up to 900,000 plants per acre, compared to just 1,600 for plants grown for flowers.

Different varieties may also exhibit unique preferences for nutrients, lighting, and harvest timing. Some strains may require higher light intensity to reach their full potential, while others might be more susceptible to nutrient burn. Harvest timing can also be adjusted to influence the chemical profile; harvesting later can result in buds with more CBN, a cannabinoid known for its sedative effects. These adjustments allow growers to tailor their methods to the genetic traits of the variety they are cultivating.