When Should I Switch My Cannabis Plants from Vegetative to Flowering Stage?

All cannabis plants that reach maturity will eventually switch from the vegetative to the flowering stage, at which point they will start developing sought-after buds that contain psychoactive compounds (THC and CBD). Properly transitioning your cannabis plants from the vegetative growth to the flowering phase is a crucial step towards a successful harvest.

The cannabis flowering stage is a crucial phase in the cannabis cultivation process. Determining the optimal time to transition your marijuana plants from vegetative growth to the flowering stage is an essential decision, as it will significantly impact your plant's health and the quality of the final harvest. Improper care or mistakes during this phase can affect the yield and quality of the bud, including its flavor, potency, and aroma.

In this guide, our experts will provide you with information on when to transition from the vegetative to the flowering stage, what happens during this transition period, common mistakes to avoid during the switch, and how to master it for optimal results.

Understanding the Vegetative to Flowering Transition of Cannabis Plants

Transitioning from the vegetative to the flowering phase is a process in cannabis plants that is determined by photoperiod. It refers to the amount of light and dark hours a plant is exposed to daily, except auto-flowering plants, which have ruderalis genetics.

All cannabis plants will switch from the vegetative to the flowering stage at some point. When growing outside, they don't need much help and do transition naturally because of being exposed to the sun. Some plants will do it automatically based on a genetically coded internal clock. However, things are different in the grow room. Plants that are grown indoors will require your help to make this transition.

In a controlled indoor growing environment, adjusting the light schedule to 12 hours of light and 12 hours of darkness (12-12) initiates the flowering period in photoperiod plants. Plants start producing flowers when the daylight hours fall below 12. This change in light indicates the end of summer and the arrival of winter, when the cold will kill the plants. Therefore, plants enter the flowering stage at this point, with the females starting to produce flowers (and seeds) and the males producing pollen sacs. This is how cannabis babies are formed.

Read More: Frequently Asked Questions About Growing Cannabis

When to Switch Your Cannabis from Vegetative Growth to Flowering Stage

Transition your plants from the vegetative to the flowering stage by switching to a 12-hour light cycle after 3 to 5 weeks of vegetative growth. Most cannabis plants are ready to flower after approximately four weeks of vegetative growth. You can transition your plants from the vegetative to the flowering phase when they reach half the overall height or width of the grow space, allowing them to mature properly.

Switching between 3 and 5 weeks is ideal for flower development and THC concentration. Some growers choose different schedules based on the climate, cultivar, and desired crop outcome.

Factors to Consider When Switching Marijuana from Veg to Flower

The timing of this switch depends on when you want your plants to flower, but that is not always an option. There are a number of factors that come into play, including the plant's height, specific strain, grow space, state of plant roots, genetics, and your needs. Here are the key factors to consider when making a transition.

Height

The vegetative stage is when a plant starts to grow to its maximum height. As long as you keep the plant at that stage, it'll continue growing taller (to a point), so consider the available vertical space. Growers who let the plants keep climbing risk damaging their plants by causing them to collide with the lights or the ceiling. To avoid such potential issues, be mindful of your strain's potential peak height and make the transition sooner rather than later if your plants are on the taller side.

Genetics and Flowering Stretch

Understand the genetic makeup of your plants since some cannabis strains exhibit strong vertical growth in a week or so after the light cycle is changed to 12/12. This "flowering stretch" can be beneficial or problematic, depending on your available grow space and needs. If you do not intend to use training techniques to keep plants under control, then you should give your plants less time in the vegetative stage to ensure they don't grow too large after the switch.

Training Techniques

The use of certain plant training techniques also determines the ideal length of the vegetative stage. Growing techniques such as low-stress training (LST) or screen of green result in earlier flowering, which helps manage plant size and optimize light exposure. However, other high-stress training techniques, such as topping or super cropping, can require a longer vegetative period to help the plant recover fully before flowering. Therefore, if you employ high-stress methods, it is best to give your plants an extra two weeks in the vegetative stage to allow them to recover appropriately.

Available Grow Space

The available grow space can determine when to transition to the flowering stage, as each plant requires sufficient space to develop buds without competition, allowing for healthy growth and maximum yields.

Therefore, it is crucial to maintain proper airflow to prevent high humidity and reduce the likelihood of fungal growth. Without adequate grow space, light will struggle to enter the plant canopy, and your plants may become starved of photons.

Optimal Yields

To maximize yield, particularly in small spaces, it is vital to optimize plant structure and height. The more bud sites exposed to plenty of light, the higher the potential yield. To achieve this, you can change the length of the vegetative phase. The longer plants remain in the vegetative period, the bigger they will become. This can be seen in monstrous plants that are allowed to veg outdoors for months and grow into tree-like structures, producing insane quantities of bud.

How to Switch Your Cannabis from Vegetative to Flower Indoors

Now, it's time to learn how to make your marijuana plants transition from the vegetative to the flowering stage in the indoor grow room.

During the vegetative period, most growers maintain an 18-hour light and 6-hour dark schedule. When plants reach full maturity for the flowering stage, you need to make adjustments so that they receive 12 hours of darkness. This means you will need to adjust the timer that your lighting system is connected to.

Once the adjustment is made, continue to care for your plants as usual, and rest assured that they will grow healthily throughout the flowering stage.

Read More: Growing Cannabis in Greenhouse

How to Switch Your Cannabis Plants from Vegetative to Flowering Outdoors

As mentioned before, outdoor growers don't have to worry about inducing flowers. Those who want a second growing cycle or an early harvest can still adjust the light and switch to the flowering phase sooner.

Growers can achieve this by building a structure over and around the plants with a removable, light-proof cover. If you keep plants covered for 12 hours a day (after they've matured), you can say goodbye to the vegetative stage. However, you should try it with caution. If you don't remain consistent with your light-deprivation schedule, the extra light will cause plants to leave the flowering stage and return to the vegetative stage.

Read More: Top 5 Irrigation Products for Growing Outdoor Cannabis in 2025

Mistakes to Avoid When Switching Cannabis Plants from Vegetative to Blooming Stage

Below are some common faults that growers make when transitioning from the vegetative to the flowering stage.

Excess Nitrogen

During the switch, nitrogen must be reduced in favor of phosphorus and potassium. If you don't make this adjustment, you will both overfeed and underfeed your plant. As a result, the plant will be at risk of nutrient burn or lockout from excess nitrogen. Still, it will also produce insufficient flowers due to a deficiency of phosphorus (P) and potassium (K). So, remember to make this change.

Switching Early or Late

The optimal timing of the switch is crucial for achieving maximum yield and efficiency. Switching too early, and plants may not mature enough to flower properly. Switching too late, and plants may outgrow their space or waste energy on unnecessary vegetation.

Knowing when to switch depends on the size of your grow space, the desired grow time, the characteristics of the specific strain you're growing, and your desired final harvest.

Too Much or Too Little Light

Providing the right amount of light to your marijuana plants is another critical element. Too little light can result in sparse, airy buds, whereas excessive lighting can stress plants and lead to issues such as bleaching or heat stress.

Providing the lighting properly requires two main steps. First, you need the right type of lights that are powerful and emit the right light spectrum. All good-quality lights can do this. Secondly, all lights need to be positioned correctly. Too far, and they'll be too weak; too close, and they'll be too strong.

The Bottom Line

The flowering stage is when all your hard work in growing cannabis begins to pay off, so it's essential to do it right and ensure your plants make that transition smoothly. With a complete understanding of the vegetative to flowering phase transition, you'll be well-prepared to manage your cannabis growth for the best possible results.

You should adjust cannabis cultivation techniques based on plant genetics, growing space characteristics, and individual plant needs. This will help you improve your plant's health and maximize high-quality yields. So, monitor your plants, stay adaptable, and be prepared to tweak your strategy as they grow.

Increase Your Cannabis Yield with DripWorks Drip Irrigation

Cannabis plants also require proper irrigation to have enough moisture for transpiration, nutrient uptake, and other metabolic processes. Therefore, it's crucial to irrigate plants effectively through an efficient system. For the biggest and healthiest yields, cannabis growers must implement a smart irrigation system, such as drip irrigation, that delivers water consistently and efficiently alongside regular monitoring using technology like soil moisture sensors.

Looking for premium irrigation supplies for watering your cannabis plants? DripWorks has been providing quality cannabis irrigation products for successful outdoor cannabis irrigation systems and indoor drip irrigation systems for cannabis greenhouses. DripWorks drip irrigation system allows you to optimize irrigation frequency and volume according to plant stage and environmental conditions. Optimal watering will help you achieve healthier plants with better structure, increased resin production, and overall yield.