As a beginner grower, there may be times when your indoor cannabis plants do not want to flower. In this article, I will explain all the possible reasons for this and highlight the potential causes. I’ll also show you how to quickly fix them and everything else you may need to consider to get back on the right track to grow some quality crops!
TL/DR
Cannabis plants require 12 hours of darkness to induce flowering and produce buds.
The wrong light spectrum can prevent plants from producing pre-flowers and pistils.
The flowering cycle requires 12 hours or less of darkness to produce cannabis buds.
The transition phase is when plants react to the switchover and stretch in size.
External light leaks can cause cannabis plants to remain in a vegetative state.
Faulty timers or ones not correctly set can cause problems with the light cycle.
Reasons Why Cannabis Won’t Flower:
Flowering your cannabis plants simply means changing the timer light cycle from 18 hours of light and 6 hours of darkness (18/6) to 12 hours of light and 12 hours of darkness (12/12). During this time, plants stretch to double or triple their height, producing pre-flowers and later buds. The flowering stage is the most exciting and anticipated stage for any grower.
Nature does not make mistakes, but there is a high chance human error may cause your plants not to flower. Below are a few of the different reasons why cannabis plants may choose not to induce flower production. The following sections will look at how to resolve them.
Timers not properly set
You would be surprised how often I didn’t set the timer properly during my amateur days. Sometimes, the timer segments are not correctly pushed down, or the switch to activate timer mode is not on. Other times, the timer is simply faulty.
Light leaks
Light from outside peeking through the zipper of a grow tent.
Considering that cannabis plants require total darkness when the lights are off, an external light source can often be the culprit to why the plants are not flowering. The tent vents may be open, allowing light to enter, or your timer may be accidentally set to unknowingly cause the lights to come on for 15 minutes during the darkness period.
Short darkness periods
Cannabis plant during the vegetative phase.
Cannabis plants require 12 hours of darkness to induce flowering and produce buds. Providing anything less than 10 hours may keep the plants in a vegetative state, especially with sativa or sativa-dominant hybrids. Learn more about the effects of different light cycles on cannabis sativa.
The genetics got mixed up
You would be surprised how often seed companies and growers contact me, wondering why their plants are having problems with flowering! Believe it or not, oftentimes, it can be down to genetics, with either a mix-up with autoflowering and photoperiod seeds resulting in a confused grower.
What to Do When Your Cannabis Plants Won’t Flower
While you may be scratching your head wondering if you have done something wrong, first of all, don’t panic. Second of all, it is not the end of the world. You just need to figure out what happened. Let’s review a short checklist of potential causes to see if any are the main causes.
Check Your Cannabis Plants are Female
Determine sex during vegetative stage
If your cannabis plants are flowering, but they aren’t throwing out bright white hair and fuzzy pistils (pre-flowers) and instead present male flowers, you need to check if the seedlings are female. If you purchased feminized seeds, but they revealed male plants, contact the seed bank and explain what happened. Be prepared with photo evidence and a positive attitude.
Are Your Weed Plants Autoflowers or Photoperiodic?
I have been in situations where growers cultivating autos did not notice any flowering signs while under 24 hours of light. A quick way to resolve this is to switch the timer to 12/12. Not only will giving the plants darkness significantly benefit the roots, but it will also kick in the flowering process much faster.
Sometimes, growers don’t know they’re growing photoperiod plants. If you thought you had autos, but they turned out to be photoperiod, there’s not much you can do apart from brush it off and start again!
Autoflowering cannabis plants will flower after 28 days, regardless of the dark period.
Photoperiod plants need at least 12 hours of darkness before they start flowering.
Is Your Light Spectrum the Right One?
The spectrum of light optimal for growing cannabis plants.
Horticultural grow lights are designed spectrum-specific, so having the correct spectrum for flowering is important. Ideally, you will want an indoor grow light that produces both blue and red light in the right quantity, hung 40-60 cm away. Lights designed for vegetative growth (blue light) will cause a cannabis plant to produce fewer flowering sites and less yield.
LED grow lights have paved the way in terms of spectrum and lighting intensity.
Avoid using low-intensity grow lights, such as CFL and 250w HPS, for flowering.
Take the time to research which Grow Light company offers the best spectrum.
Is Your Day/Night Cycle 12/12?
The first time I grew plants indoors, I did not know that you had to actually change the light cycle. I naively assumed they would just start producing buds, and the rest was history. Now, I can look back at that point and laugh but don’t make my mistake. Is your light cycle actually set to 12/12? Double-check, as there could always be a chance the timer has not been activated and is still operating on a vegetative cycle.
The vegetative stage requires 18-24 hours of light to grow leaves, stems, and roots.
A flowering plant needs 12 hours or less of darkness to produce cannabis buds.
The transition phase is when plants react to the switchover and stretch in size.
Are There Any Light Leaks in Your Grow Tent?
The reality is you may not even know! But it’s important to check; light leaks are one of the easiest ways to cause indoor plants to remain in a vegetative stage. This problem often occurs when cannabis growers have house lights or a bedroom light on with the side vents fully open.
Turn off any bedroom or landing lights if you are growing with a tent in your bedroom.
Do not allow the light from outside to enter the room when the plants are in darkness.
Some of the timer segments may not be pressed down, causing 15-minute light breaks.
What if the plants are flowering during 18/6?
Then Houston, we have a problem! I have seen this happen with clones that were sensitive to light cycles and, as mentioned above, with mix-ups from seed banks between photoperiod and autoflowering cannabis seeds. You may also be causing the issue unintentionally due to a faulty timer or experiencing power cuts without knowing it.
Conclusions
When you have a cannabis plant that’s showing no signs of flowering or expressing a stubbornness to flower, try to figure out the cause. Step back and work through all the variables covered in this article. Don’t let it set you back too much. Apart from losing out on time, nutrients, and potentially the cost of a pack of seeds (which may be refunded or replaced), there is no real loss. There is, however, a valuable lesson learned. You learn from experience. Over the years, I have tried all sorts of experiments with light cycles with indica, sativa, and hybrids. Go more in-depth by reading about the effects of different photoperiods on cannabis plants.
My best advice is to double-check that your timer segments are fully pressed down and that the timer is set to activate in timer mode. You would be amazed at how many growers make this simple error. Otherwise, spend the time to purchase top-quality seeds from seed banks such as ILGM and a well-designed grow light with the ideal light spectrum. Hopefully, you never even experience a cannabis plant that does not flower, but it can happen, so always be prepared.
Comments