Wondering how to change light cycles in your home garden? High Times Cultivation Editor Nico Escondido answers all of your grow questions in his weekly Nico’s Nuggets column.
The Question: How Do You Change Light Cycles From The Veg Phase To Flowering?
Dear Nico,
Thank you and High Times so much for staying dedicated to the true cause of the movement. Teaching the world to grow is the best way to mitigate the unrealistic laws of marijuana prohibition.
That said, we are about to start our first indoor garden! (We usually grow outdoor, but winter is coming…) We want to be sure we have everything covered before we start. We have both MH and HPS bulbs to use with a switchable ballast and want to ask about how exactly (and when) to change light cycles from the vegetative phase to the flower stage?
We want to induce flowering at the right time for optimal harvest and peak potency. Thanks to you and High Times for years of great work!
— Scott & Kelly M.
The Answer: Learning The Basics Of Light Cycles
Greetings Scott & Kelly,
Thanks for the kind words and for writing in with a question. Light cycles for indoor gardens are always a concern the first time during an initial grow. But once you get the basics down, it will be an afterthought moving forward.
To start, the first consideration will be just how big you want the final size of your plants to be. Working backward, the final size of your plants at harvest will largely be determined by how long you keep your plants in their vegetative phase.
How long you decide to “veg” your plants will also determine when you change the light cycle to induce flowering.
Most indoor home growers have limited space, so a two- to four-week veg is generally the standard.
However, if plants are put into flower production too early, they will not have enough energy reserves (stored in the root structure, which will be too small to store large amounts of energy) to produce big yields. That is why growers who utilize a short two-week veg period are usually growing a large volume of smaller plants in a sea-of-green (SOG) format. (The large volume of plants makes up for the smaller yields per plant.)
Most indoor growers do not have space to grow dozens upon dozens of plants, so many opt for fewer plants with a longer veg time and, thus, a larger final plant size for larger yields at harvest.
It is important to remember that once the light cycle is switched for flowering, plants still have another seven to 10 weeks of growth and will double in size—if not a bit more.
So if, for example, you want to have a final plant size of 3’ at harvest, then put your plants into the flower phase once they reach 15” – 18”.
This is an important aspect to consider, especially if you are using a grow tent or a space with limited height.
Also, remember that indoor lamps hang directly above garden canopies and further cut down on over-head space for plants to grow. (Note: Grow lamps should hang a minimum of 18” above plants and will need to be adjusted periodically as plant height increases.)
Once you decide on your vegetative timetable, it is time to think about how you will switch the light cycle.
Most growers use an 18-hours on/6-hours off light cycle for the veg phase. Some prefer to use 20 on/4 off, which is also acceptable. However, stay away from 24 hours straight light during veg, as this does not allow any downtime for the plant, not to mention the roots grow and develop the most during the dark cycle when the rest of the plant “sleeps.”
At the end of your vegetative phase, growers then change the light cycle to an even 12-hours on/12-hours off.
Cannabis plants rely on the photoperiod, or amount of daylight received, for their internal biorhythm to determine when to begin flowering. Receiving 12 hours (or less) of light will trigger the flowering phase.
To make the change from 18/6 or 20/4 to the required 12/12 light cycle, growers adjust the timers that their lights are on.
To do this with minimal shock to your plants, simply extend the time of the lights-off cycle to 12 hours at the start of the dark cycle, making sure the lights-on cycle is also set to 12 hours. Check the growroom at the start and end of each 12-hour cycle for the first two days to make sure the timers are set correctly. After that, it is just a matter of time until harvest.
Certainly! The article you've provided focuses on changing light cycles in an indoor garden when transitioning plants from the vegetative phase to the flowering stage. Here's a breakdown of the concepts covered in the article and an explanation:
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Indoor Gardening Basics:
- Light Cycles: The article delves into the importance of light cycles in indoor gardening. The length of time that plants receive light each day has a significant impact on their growth stages.
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Vegetative Phase & Final Plant Size:
- Determining Final Plant Size: The duration of the vegetative phase affects the ultimate size of the plants at harvest. The longer the plants are kept in this phase, the larger they will grow.
- Consideration for Space: The space available for growing indoors influences decisions regarding plant size and number.
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Transition to Flowering:
- Optimal Time for Flower Induction: The decision to induce flowering is based on the desired final plant size. For instance, if a 3’ plant height is preferred, transitioning to the flowering phase around the 15” - 18” mark is recommended.
- Growth During Flowering: Plants continue to grow significantly during the flowering phase and may double in size or more.
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Light Cycle Adjustment:
- Vegetative Light Cycles: Common vegetative light cycles include 18 hours on/6 hours off or 20 hours on/4 hours off. Continuous light (24/0) during the vegetative phase is discouraged.
- Transition to Flowering: The critical shift from vegetative to flowering stage involves adjusting the light cycle to 12 hours on/12 hours off. This change triggers the flowering phase by mimicking the natural photoperiod that signals plants to start flowering.
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Light Cycle Adjustment Process:
- Implementation of Light Cycle Change: To transition smoothly, growers extend the dark cycle to 12 hours while ensuring the light cycle is adjusted accordingly.
- Monitoring Post-Change: Regular monitoring during the initial phase of the new light cycle is recommended to ensure proper adjustment.
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Light Height and Space Considerations:
- Light Height and Plant Growth: Lights hanging above the plants affect available vertical space. Adjustments are necessary as plants grow to maintain adequate distance between the lights and plant canopies.
The article provides comprehensive guidance for novice indoor growers, covering aspects from determining plant size to managing light cycles during different growth phases for optimal cultivation.
As an expert in indoor gardening and cultivation methods, I can affirm that managing light cycles is crucial in controlling plant growth stages and maximizing yield in indoor gardening setups. Adjusting the light schedule during the transition from vegetative to flowering phases is a key practice to ensure successful cultivation and a bountiful harvest.
