When is the Ideal Time for Switching to Flowering Nutrients?

If only growing cannabis were as simple as its nickname would suggest. Cannabis, unlike weed(s), requires strict conditions and precise doses of nutrients to flourish. Whether in or outdoor growing, the ideal environment is imperative. Specifically, knowing the exact moment to switch to flowering nutrients is one of the most important steps to a successful yield.  

When to switch to flowering nutrients is subjective but largely depends on growing location. For indoor plants, growers generally aim for 4 weeks of vegetative growth. Outdoor growers have less control, as plants tend to flower on their own mid-summer. 

Other factors should be considered, like the strain of the cannabis plant or if the plants are grown from seeds or clones. When growing cannabis, adapting to your plant’s specific needs and preferences is more important than copying methods used by other growers. 

When is the Ideal Time for Switching to Flowering Nutrients?

Knowing how environmental factors affect your plants is key in finding an ideal time for switching to flowering nutrients. If you are growing indoor plants, you have much more control over this transition. In theory, indoor plants could stay in a vegetative state forever if the conditions are right. Consider these factors before making the switch:

  • Plant height: growing indoors means limited space. Leaving your plants in the vegetative state too long could result in overgrowth and burned buds and leaves if they grow too close to bulbs. Consider that plants can almost double in height once they being flowering to know when to switch. 
  • Strain: Sativa plants are known for their size and may double in height between the flowering and harvest stages. Indica strains are bushier and generally produce shorter fuller plants. They can grow anywhere up to 50% of their original height. Make sure to carefully research the specifics of hybrid strains. 
  • Growing method: different growing methods, like SOG (sea of green) or SCROG (screen of green), will call for different lengths of vegetative growth. The SOG method requires a shorter vegetative stage than the SCROG method. 
  • Clone or seed: seed-grown plants can be flowered much quicker than clones, generally in about 2-3 weeks. Height is the main factor in switching to flowering nutrients with clones, as they tend to grow quickly. It is key that the plant has established a good root system for healthy growth in either case. 

For outdoor cannabis plants, conditions vary and are harder to control. The main thing to consider is sunlight. Shorter amounts of sunlight, around 12 hours a day or less, will trigger the plant to naturally begin flowering on its own. Light exposure is the key tool for when you decide it’s time for your plants to flower.  

Whether indoor or outdoor, creating the right conditions for your plants to grow is essential in choosing the right moment to switch to flowering nutrients. More importantly, understanding the actual biology of the flowering process will guide you to more skillfully determine the most ideal time to make the switch. 

The Biology of Flowering  

Knowing when to switch to flowering nutrients means knowing when the flowering process should begin or has already begun. Like many other short-day plants, cannabis requires darkness to trigger the hormones that kick off the flowering process. Indeed, it is photoperiodism that is the catalyst to the flowering phase. 

Many growers focus mainly on the amount of light exposure plants should receive; however, darkness is just as important, if not more, to flowering. In the vegetative phase, light receptors in the leaves called Pr (phytochrome red) and Prf (phytochrome far-red) react with light. Different ratios of light, in turn, trigger differing ratios of phytochromes. 

In the presence of light, the Pf and Prf are balanced. Darkness decreases Pfr, and inversely, Pr multiply. Pfr tells the plant to continue vegetative growth. Therefore extended periods of darkness eventually cause Pfr levels to drop below a threshold, triggering the plant to flower. 

Outdoor plants being flowering naturally at the end of summer, as days get shorter and plants receive less than 12 hours of sunlight. Keep in mind that even outdoor growers may trigger the flowering process by covering plants, and therefore reducing their sun exposure. 

Indoor cannabis trees are manipulated into flowering once a grower assesses factors like the height and age of a plant. Overgrowth is the main concern. Once plants reach about half their desired size, you should consider making the switch to flowering as plants double and even triple in size while flowering. After about two weeks, you should see buds beginning to form. 

Vegetative V.S Flowering nutrients  

Plants generally get nutrients they need from their environment, however helping them reach their ultimate potential means supplementing. Seedlings don’t require any nutrients as they simply absorb water through their roots and leaves as they grow. In 3 to 4 weeks, the seedlings will enter the vegetative growth stage. This is a good time to begin feeding them.  

When it comes to determining ratios, the main focus is the macronutrients of nitrous, phosphorous, and potassium, or NPK. Secondary nutrients are also important and include:

  • Calcium 
  • Magnesium 
  • Sulfur 

In the vegetative state, starting on a low ratio of 2:1:2 (NPK) is a good place to start. If you overload your plants with too much, too soon, you may experience nutrient burn. Nutrient burn can severely damage yields. After about 6 weeks, growers increase these ratios to boost foliage growth. In the last week of vegetation, many growers opt for an even ratio of 7:7:7. 

Lowering to an even ratio prepares the plants for flowering nutrients, as flowering plants don’t require as much nitrogen. It is important to note that potassium levels must be consistently higher than nitrous and phosphorous concentrations throughout this stage to promote healthy and vigorous flower growth. Start at a ratio of 5:7:10, then build up from there. 

Mid-late bloom is the time to gradually start bringing our NPK nutrient ratios back down to prepare for harvest. On average, you should be feeding your plants about once a week throughout the flowering process to optimize growth. 

Feeding your plants the right nutrients at the right time is monumental in a successful harvest, but is not the only thing to consider. Other environmental factors, like humidity and heat, can greatly influence how your plants grow, and therefore the flowering timeline of your plants. 

Ideal Conditions for Growing

Ideal conditions mean optimizing each stage of growth. A successful vegetative stage will mean moving into flowering quicker and better identifying the right time to switch to flowering nutrients. Focus on the right humidity, temperature, nutrients, and trimming methods to contribute to your success. 

Growing strong plants with healthy leaves and branches is a crucial step towards moving into the flowering stage. As plants take in water and nutrients, they simultaneously release moisture into the air. For indoor plants, high humidity levels can promote unhealthy growing conditions and extend an invitation to unfriendly guests, like mold and pests. 

Ideal conditions call for a 40 to 50 percent humidity level. Use a dehumidifier to monitor these levels and ensure your plant is healthy enough to flower. 

Trimming your plants is also key for this reason, especially in the flowering stage. Pruning your plants ensures that airflows freely between leaves and branches to prevent mold and mildew growth. Trimming lower branches also promotes top growth, meaning plants grow taller and get more sunlight. 

Focusing on creating the right environment for vegetative growth will ensure that your plants will be strong enough to carry and grow flowers. Switching to flowering nutrients, and therefore moving into the flowering stage, is only possible after building a strong foundation of vegetative growth. 


Knowing when to switch to flowering nutrients is directly dependent on when your cannabis plants enter the flowering stage. Indoor plants will need to be triggered to flower, while outdoor plants generally flower on their own due to a change in seasons. 

Therefore, focusing on the length of light exposure that your plants receive is the key element in knowing when to switch to flowering nutrients. Using light as a tool will lead to the successful cultivation of your cannabis plants, and generous flower yields. 



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