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What To Do If Your Cannabis Won't Flower

Last updated: 3 October 2022

flowering light cycle interrupted

So you have taken care of your cannabis plants for weeks, nurtured them during the vegetation period and made sure you tended to all their needs – you fed them, watered them, provided them with sufficient light and shielded them from damage. But despite the care you took, you notice your marijuana not flowering. Let’s discuss some important factors to consider that are potentially holding your cannabis back from flowering.

Things To Check If Your Plant Fails To Flower

Follow this checklist to make sure your plant growing plan is fail-proof. Even a little inconsistency can prove to be quite problematic and be the reason behind your cannabis not flowering.

Is Your Plant A Male Or A Female?

force flowering cannabis outdoors

This may sound like a silly thing, but quite a few novice growers tend to be unsure whether they’re growing a male cannabis plant or a female one. Let’s put this straight – it’s only female plants that flower and provide resinous nugs rich in THC and other cannabidiols. If you’re growing a male, it will unfortunately never grow buds, so you shouldn’t be expecting any flowering at all. Identifying a male cannabis plant is easy, as all you need to do is take a peek at its nodes. The nodes are present where the side branches and leaves grow from the primary stem.

To simplify things even further, males have pollen sacs, while females tend to develop small pre-flowers. Telling them apart can be tough initially, but if you wait for a day or so, things will become clearer. The females grow small pre-flowers that look like tiny knots of hair, while the male’s pollen sacs will keep multiplying until they appear like clusters of tiny grapes.

Is It An Autoflowering Variety Or A Photoperiod?

autoflower won't flower
Autoflower                                                   Photoperiod


Check whether or not the plant you’re growing contains autoflowering genetics. Do you plan to get your autos to flower in just under a day of light? If the answer is yes, it would be advisable to cut back on the light, ideally to 18 hours on schedule and 6 hours off. The old-school autos, in particular, contain a higher Ruderalis percentage, which is why they bloom rapidly and on their own once the plant reaches third-week post-germination. The plant will still bloom even if the lights stay on all throughout the day.

That being said, many breeders have been able to increase the yield of autoflowers by lowering the quantity of Ruderalis in the newer autos, and hence will recommend having some hours with the lights off. If the stills don’t start forming within a couple of weeks of 18 by 6 lighting, it’s possible that the plant you’re growing is not of the autoflowering variety, but rather a photoperiod one.

Novice growers often forget that photoperiod strains don’t flower unless they get at least 12 hours of uninterrupted and consistent darkness. It doesn’t matter how old or how big the photoperiod plants are becoming; they’ll fail to flower without adequate time in the dark every day. If you plan to grow photoperiod plants alongside your autos, you don’t need to fret about decreasing 6 hours of light for your autos – this will not damage the plant; in fact, it might even be helpful.

Are You Using The Right Light Spectrum?

marijuana not flowering
Blue spectrum light for vegetation               Red spectrum light for flowering


Even if you’re a novice grower, you must have at least some understanding of proper lighting for weed cultivation. The first thing to keep in mind is that red spectrum light is an ideal choice for flowering, while blue spectrum light is ideal for vegetation. So, if everything else about your plants and their conditions seem correct, the delayed flowering might be caused by the mistake in choosing the light spectrum. You can easily fix your indoor growing troubles by getting a blue/red spectrum light – for example, an LED. However, if you don’t want to get an LED or HID, which also provides the full spectrum, you can simply change your lights between different spectrums during the plant’s growing cycle.

Now, if you combine this info with the facts from the previous segment of this article, you should understand that the key to making the successful flip into flowering is not only 12 hours of dark for photoperiods, but also red spectrum for when the lights are on – true for both photoperiod and autoflowering strains.

Likely Reasons Why Your Plant Fails to Flower

There are plenty of reasons why plants might fail to flower properly. However, in most cases, it’s the interruption of the light schedule. Novice growers often don’t have the slightest idea about adequate light provision, but finding the right balance is key to ensure that the plant flowers at a decent pace.

The Light Was On For An Extended Period

force auto flower to flower

Mostly, you will not notice too much of a difference if you leave the light on for a day in the vegetative stage or even the beginning of flowering. However, if you leave it on for several days straight, there will be a noticeable change. Your plant could take much longer to flower or even regress to its previous vegetative state during early flowering. As the plant comes closer to maturity, extra exposure to light impacts its growth.

In order to prevent this from happening, you must get the lighting cycle right. 12 hours on and 12 hours off is the perfect lighting time to promote adequate growth for your photoperiod strains. Try not to interrupt this lighting period at all.

There Were Light Leaks In Your Growing Area

cannabis not flowering

Any interruptions or leaks can prove to be quite detrimental and potentially prevent your plant from flowering. Furthermore, it could also force it to go back to vegetative growth once flowering has already started. According to some expert growers, even a torch or flashlight could hinder your plant from flowering.

First off, if you’re growing indoors, you must thoroughly inspect the room for leaks and address the problem immediately by covering the areas that are letting light inside. You should also get an automatic light timer, as this will offer you a lot of ease in following your plant’s light schedule.

You Forgot To Switch Off The Light During Dark Time

cannabis flowering problems

People who are new to cannabis growing often forget to keep track of their plant’s light and dark time, no matter how simple it is. As mentioned before, if the light stays on during the dark time, your plant’s growth could go haywire. Sure, some strains might be able to tolerate the extra light, but you should never take that risk. Instead, what you should do is properly set a light timer and follow it scrupulously. Once again, when it comes to growing photoperiod strains, 12 hours on and 12 hours off schedule works best to ensure flowering – a simple rule to remember that will help the plant flower quickly.

A Simple Fix

force flowering cannabis indoors

The importance of adequate light and dark times cannot be stressed enough. An interrupted flowering light time always leads to bad results. Fix your light schedule and you will see tremendous rewards. Also keep in mind that too much dark time could also be detrimental to your plant’s flowering. Light is a vital part of a plant’s nutrition – too much of it could be damaging, but too little could malnourish it. Once again, balance is vital, and having an uninterrupted schedule will most likely fix these problems for you.

Bottom Line

flowering light cycle interrupted

If a grower is patient enough, has female plants, and also has the right dark and light cycle in place, they will effectively solve most of their cannabis flowering problems. Shortly after this, calyxes will begin to form and start swelling up. Once that happens, it becomes apparent that all of their effort in sticking to the correct light schedule will soon pay off!

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