ALL ABOUT DIMMING: SPEEDING UP FLOWERING OF CANNABIS PLANTS

You can speed up the flowering of photoperiod cannabis plants by going blackout. That means making sure your plants get less than 12 hours of daylight a day. This allows you to harvest earlier and prevents your crop from falling into bad autumn weather. We explain how to do darkening in this blog.

What is darkening to speed up flowering?

Normally, photoperiod cannabis plants naturally transition into the flowering phase when it is dark for more than 10 hours a day. This happens logically when the days get shorter again at the end of summer, in late August. The fact that the light is shorter means it is time for the plant to produce buds.

Indoor and outdoor cannabis growing tips

When growing indoors, you can easily influence the amount of light your plants get. When growing outdoors, this is more difficult, but not impossible. You then use a technique called blackout. This allows you to force your cannabis plants to enter the flowering phase earlier, by putting them in the dark, so to speak. This causes them to flower a few weeks earlier. Darkening is not difficult, but it does take a lot of time. After all, you can't skip it for a day.

Why darken?

As mentioned, photoperiod cannabis plants enter the flowering phase at about the end of August. In the Netherlands, that means autumn is already starting to set in and your plants will have to deal with wind, rain and grey, dreary days. The poorer weather increases the risk of fungi such as mildew or bud rot, the buds can deteriorate in quality and the plants can be damaged by strong winds. Therefore, it can be advantageous to bring the flowering phase forward. And this can be done by darkening. When your weed starts flowering (forcing flowering) earlier, the plant still benefits from the good weather, from powerful sun and warmth. And if all goes well, you can enjoy your wonderful harvest as early as autumn.

That sounds great, of course, but there are some drawbacks to dimming. By encouraging your plant to flower earlier, it does mean that it cannot grow as long. As a result, the root system may not be as well-developed and the plant will remain smaller than it could have been. Of course, growing longer also means that your plant will become stronger and bigger. So make sure you only darken when your plants are big enough, otherwise you might end up with a lower yield.

Dimming is also quite a time-consuming technique. Every day you have to put your plants in the dark at the same time. And the next day, you have to let the light back in at the right time. You need time for that, and not everyone will have it.

Accelerating flowering: how do you go about it?

There are several ways you can put your cannabis plants in the dark.

• Darkening tent: You can make this yourself by making a frame to put your plants under. Cover the frame with thick foil, with a black and white side. Make sure the black side is on the inside. Fix the foil so that no light can get in.
• Bags (such as rubbish bags): Put a large plastic bag over a single cannabis plant so that no light can get in. If you use a rubbish bag, then one is probably not enough.
• If your cannabis plants are in pots, put them indoors every night in a shed or bedroom that you black out.
• If you grow in a greenhouse, you can also darken it properly using black-and-white film. Cover the greenhouse with this until it is well light-proofed.
  
  

When do you start darkening? The best time to do this is in mid-July. The summer sun still shines strongly then and you stop darkening at the end of August. In north-western Europe, the nights are then long enough that your plants will continue to flower on their own. The best time to start darkening is up to you. In general, between 8 p.m. and 10 p.m. is most convenient. In any case, they need to be in the dark for at least 12 hours. So that means, if you choose 8pm to darken, put them back in the light at 8am.

What is important when darkening?

There are a number of points to keep in mind when growing cannabis outdoors and going blackout. Avoid light leakage. If even a little light seeps in, it can ruin your whole project. You black out so that your plants get some rest. But if light does get in, it will cause stress and that will disrupt flowering considerably. In the worst case, your female plants can become hermaphrodites and will not flower.

Also make sure you have a set rhythm. Stick to your scheduled times. Your plants will get used to this rhythm and this will keep stress as low as possible. Again, if there is stress, it can interfere with flowering. It is also a good idea to check your plants for fungus, which is more likely to occur if you cover them with plastic. Also make sure you are careful when darkening. The plastic covers, bags and moving can cause damage.

To darken cannabis or not?

As you can see, darkening your cannabis plants has quite a few advantages. But it is also a time-consuming job. Is it worth the effort? Only you can decide that. You can try it once. If you don't want to put so much effort into speeding up flowering, you can always opt for convenience and go for an autoflower strain. These automatically switch to the flowering phase after a few weeks, regardless of the light. They start flowering as early as mid-July, allowing you to harvest by the end of August. Check out our shop for the wide range of autoflowering strains. If you want to know more about growing cannabis outdoors, read this grow report!

Sources:

There are several scientific studies investigating the relationship between light cycles and flowering of cannabis plants. Here are some relevant articles:

1. "A Study of Two High-THC Cultivars Grown under 12 h vs. 13 h Days".
   Summary: This study investigated the effect of a 12-hour versus a 13-hour light period on the flowering and yield of two THC-rich cannabis varieties. The results showed that some indoor-grown cannabis varieties can exhibit a strong flowering response under daily light periods longer than 12 hours, which can lead to increased growth and yield. PMC
   
   
2. "Moving Away from 12:12; the Effect of Different Photoperiods on Biomass Yield and Cannabinoid Concentration in Cannabis sativa L."
   Summary: This study investigated the effect of different flowering photoperiods on biomass yield and cannabinoid concentration of three medicinal cannabis varieties. The results suggest that photoperiods longer than 12 hours can delay flowering but potentially affect yield and cannabinoid profiles. PUBMED
   
   
3. "Optimising Photoperiod Switch to Maximize Floral Biomass and Cannabinoid Content in Cannabis sativa L."
   Summary: This study investigated how the transition between long and short day lengths affects the yield of C. sativa. Results showed that floral biomass was maximised when the long daylight photoperiod was minimised (i.e. 14 days), while THC and CBD potency was maximised under longer daylight photoperiods. PUBMED

These studies provide insight into how variations in light cycles can affect flowering and yield of cannabis plants. When growing cannabis, be sure to always check local laws and regulations for legality beforehand.