When To Switch Your Cannabis Grow From Vegetative To Flowering

Knowing when to flip your grow from the vegetative to the flowering stage is one of the most important factors to ensure the success of your plants. This is because making the switch too early can result in a smaller total yield. Conversely, making the switch too late can result in overgrowth, or burned buds. The decision to make the switch should be based on the careful consideration of numerous factors such as the age of the plant, the maximum height that the plant can obtain within your setup, the type of strain(s) being grown, the source of the plant (from seed or clone), and the growing method being employed.

When making the switch, growers need to be aware of all of these conditions, and of the ways in which they can affect the final product. Since each grow is unique, growers should be careful when copying the methods and techniques used by others. They may actually end up giving you dramatically different results than what you intended.

Does Plant Age Matter?

Sort of—not really. Some growers believe that plants grown from seeds must be given 60 days of maturation in the vegetative state. However, this is not necessarily true. It is important to remember that young seedlings cannot start properly flowering for 2–3 weeks. However, when growing from clones, age is not an issue. Growers can switch to the flowering stage as soon as the clone has established a solid root system.

In optimal conditions, plants should be kept in their vegetative stage for approximately 60 days. This time period should give the plant the opportunity to maximise yield and acclimatise to growing conditions. This is important because complications and mistakes are much more difficult to recover from during the flowering stage. It should be noted that this time period is just a recommendation. If maximum yield is not a priority, or if growing conditions will not permit for a lengthy vegetative stage, plants can be flowered long before the 60-day benchmark.

Factor #1: Maximum Plant Height

The most important consideration is the amount of space available for your plants. The longer that plants are kept in a vegetative state, the taller they will become. As such, vegging your plants for too long in a confined space can result in an overgrow situation. Plants that grow too high can potentially reach too close to light fixtures and suffer damage as a result. Ideally, you should never let your plants reach closer than 30cm from the lights above them. This is a rough estimate. However, growers risk burning or frying their buds if they allow them to reach any closer.

Be sure to consider the light fixtures being used in the grow. Some bulbs glow hotter than others, and this will certainly affect the minimum distance that should be kept between the plants and the lights. How long you let your plants grow in their vegetative state should also depend on the kind of strain that you are growing.

Factor #2: Strains—Indica Or Sativa?

The genetic differences between indica and sativa strains must be considered when making the switch to the flowering stage. That is because indicas and sativas behave differently during flowering. Indica strains are known for producing shorter, thicker, bushier plants when compared to their sativa counterparts. Typically, they will gain only 25–50% of their height in the flowering stage. By comparison, sativas are known for their height, and for their ability to keep growing taller throughout the flowering stage. They have been known to double their height from the first day of flowering until harvest.

Keep in mind that these characteristics apply to pure sativa and indica strains. Most strains will demonstrate characteristics representative of both kinds since they are not 100% indica or sativa. When dealing with hybrids, make sure to research the genetic makeup of the plant so as to have a better idea of what to expect during the grow. A basic rule of thumb for growing hybrids is to expect that the plant will grow to be twice the height it is at the end of its vegetative state.

Factor #3: Clones Or Seeds?

The planting method chosen for the grow will also affect the timing of the switch. The difference between growing from seeds or clones will affect the growth rate of the plant’s root system. If the plant has not established a solid root system, then there may be issues and complications during the flowering stage.

Clones can grow very tall very quickly, forcing growers to make the flip to flowering based on plant size alone. However, growers should make sure to give their clones the necessary amount of time to establish themselves before flowering. Seedlings can be flowered much earlier, but remember that they will require 2–3 weeks before being able to do so.

Factor #4: Growing Methods

Different growing methods such as the sea of green (SOG) method, the screen of green (ScrOG) method, lollipopping, and super cropping can all affect the switch. Depending on which method you choose, your flowering time will likely be different.

• Sea of Green (SOG)

This method relies on flowering plants early so that they only produce one large bud. This method is usually employed with indica strains that are packed tightly together in the grow space. When using this method, plants should be flowered when they reach a height of between 15–30cm. 

• Screen of Green (ScrOG)

This method utilises a mesh screen that is layered horizontally above the plants. The screen is typically placed 30–60cm above the base of the plants. This allows them to grow right through it. When using this method, plants must remain in a vegetative state for several more weeks than with the SOG method. 

• Lollipopping

Lollipopping is a technique that involves removing the lower growth of the plant that receives very little to no light. Because plants need light to grow, these regions will produce smaller buds and drain the plant of energy that could be better spent elsewhere. By removing the lower leaves and bud sites, the plant can focus its energy on the upper colas that grow denser, thicker nugs. This method typically involves a height-based flowering switch. Sativas are usually switched when they reach 30–45cm, since they grow so much during the flowering stage. Indicas are switched when they reach a height of around 100cm, giving them more time in the vegetative state.

• Super Cropping

This method is designed to produce very heavy yields from a minimal number of plants. As such, plants grown using this technique need to remain in the vegetative stage for longer. Super cropping involves bending upper branches down so as to allow more light to reach the lower parts of the plant. This keeps the height of the plant in check throughout the grow, and allows for a longer vegetative period.

Outdoor Considerations

Typically, outdoor growers allow their plants to flower by themselves. This usually occurs after mid-summer when days become shorter than 12 hours. Outdoor growers should take care to ensure that their plants do not receive any kind of light at night. This includes light sources such as garden lights, street lights, or spotlights.

However, outdoor plants do not necessarily need to be left to their own devices. Similarly to indoor plants, they can also be forced to flower by a change in conditions. Some climates simply do not offer plants enough time to flower before winter. Other climates may require a grower to force flowering so as to keep the plant in check. Additionally, some growers choose to force flowering in order to harvest multiple grows during the same season.

Whatever the reason, forcing outdoor plants to flower is a simple process. Outdoor growers usually force flowering by covering up their plants, reducing their exposure to sunlight as a result. Cultivators using greenhouses simply need to cover the windows of their grow room. 

What To Expect When Flowering

For most cannabis strains, the flowering period will last somewhere between 7 to 10 weeks. What happens during this period will vary from week to week and strain to strain. For more information about what you can expect during the flowering period, check out the week-by-week Royal Queen Seeds flowering guide.