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Light Deprivation

What Is Light Deprivation?

When growing Marijuana outdoors, the use of light deprivation techniques can allow a grower to control the number of hours of light the plant will receive. Depriving the plants of light is something that can be incorporated when there are more than 12 hours of available daylight per day. By tricking the plant into thinking that the long summer days are over and the short light periods are beginning you can speed up the flowering process. This means that even if you are growing Marijuana outdoors, you can harvest late blooming plants before the autumn weather arrives.

What Times Of The Year Can I Use Light Deprivation?

The amount of daylight in the northern hemisphere in September is around 12.5 hours. Then during winter the days end quickly and sunlight is only available for around 7-9 hours. Plants that normally finish their flowering period in October or even November are very susceptible to bud rot due to the temperatures and weather conditions during these months. By depriving plants of light you can trigger the flowering process earlier, the best time to do this would be in the beginning of July. After July, the hours of light per day will decline, and it will not be necessary to keep covering your plants.

The average amount of hours of light per day in the last few months of the outdoor season in the Netherlands are as follows:

  • July - 16.5 hours
  • August - 14.5 hours
  • September - 12.5 hours
light deprivation and hours of daylight
Tip: Make sure your plants only receive 12 hours of sunlight during the first three weeks of July. After these three weeks the flowering process is in full effect and there are less hours of light per day, so there is no need to keep covering your plants. By using light deprivation for the first three weeks of July when growing Marijuana outdoors, even indoor Sativa varieties will be ready for harvest before the weather turns bad!

What Can I Use To Cover Plants?

You may only require to deprive a small number of plants or you may have an entire greenhouse to cover. The important thing to remember when growing Marijuana outdoors and using this technique, is to ensure the cover you make is completely light proof. In the event that your cover lets light through at any point, the plant will likely respond with hermaphrodite traits.

A thick black plastic cover that fits over the plant (and its container) can work well, whilst white covers will not usually not keep out all the light. Small plants can even be placed in a shed and kept in the dark. Other methods include to placing the plant in a black plastic bin for the duration of the technique. If you have a terrace for example then bringing the plants into a dark room that will not be disturbed is perfect. This can be laborious work but it can also be well worth it in the end.

light deprivation example
Tip: Invest time and money into your light deprivation project. By not putting in the extra work when growing Marijuana outdoors, your plants may develop seeds or grow badly. Also keep an eye on the inside of plastic containers as these can develop moisture buildup, especially when they still catch direct sunlight. It may not always be possible to keep the plants in the shade when covered. Lastly, prepare yourself for the size some plants are able to achieve even in a relatively short vegetative period. After a few months of growing, it can be difficult to cover an entire Sativa plant for example. If you add in the amount of stretching that usually goes along with the start of flowering, it becomes very easy to underestimate the required size of your cover.

Morning Or Night Best Time To Cover?

There are two ways of depriving plants of light: in the morning or in the evening. It is up to you as a grower to decide which is most suitable, as long as the plants don’t get more than 12 hours of light.

It is however important to be consistent with when you deprive your plants of light. If you start by applying light deprivation in the mornings, then keep doing this in the morning. By switching back and forth between applying light deprivation techniques in the morning and evening, you may not obtain the desired results.

Tip: Be stealthy! If you live in an area with neighbors close by then moving plants inside and outside may catch the wrong attention. Try to keep your plants out of view as a plant that is visible at one moment then covered up the next can also look suspicious.

What If I Have A Window That Receives Sun All Day?

A grower can create space on a windowsill indoors for a plant to grow if your windows let enough sunlight through. You may have a number of plants in a room that is exposed to sun for long periods of time. This a perfect scenario to perform light deprivation as you can simply use a curtain to obscure the daylight. The good thing about this style of growing is that during the night, the plants will be kept indoors where they are safe and sound. By simply rolling down a thick curtain and ensuring no light leaks are possible, this cheap and effective light deprivation technique can produce excellent results in a way that is very similar to growing Marijuana outdoors.

example of windowsill light deprivation
Tip: Using a timer and an electric curtain rail can really save time, as well as ensure the plants receive 12 hours of light. Performing these techniques manually and by the clock can never be 100% reliable. In Spain and around the Mediterranean, this technique is incorporated a lot as growers cannot always be on site to perform the task.

The following video shows that light deprivation can be performed on a massive scale and that even commercial greenhouse growers incorporate this technique. Because light deprivation is completely automated in the video, the grower is able to accurately control the number of hours of light:

Can Light Deprivation Be Done With Autos?

There is no need to deprive autos of light and in the event of light deprivation, this will only reduce the final yield. Automatic strains perform best with 13-18 hours of sunlight so the more light the better. If you intend to use light deprivation techniques when growing Marijuana outdoors, keep in mind that this is only possible with photoperiod strains.

Two Harvests In A Year!

Light deprivation can also be used to be able to harvest twice in one year. For example if you have 10 plants, you would grow 5 plants normally and 5 plants with a light deprivation protocol. This way you can harvest half of your crop much earlier than normal. Depending on when you start the light deprivation regime, this could be as early as August. The other 5 plants can then be harvested in October or November after their normal flowering period.

Tip: Experiment with light deprivation from April until August to see which part of the year produces the best overall results. Different times of year create different environments and the challenges of insects, bud rot and powdery mildew are always around the corner.

For more tips regarding outdoor growing, please check out our guide to maximizing your yield when growing Marijuana outdoors.

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