by Seshata on 17/04/2015 | Cultivation

Outdoor tutorial: force-flowering

Tutorial Growing outdoors can be tricky in terms of timing, and if you get it wrong--or if your location simply does not allow you the leisure of letting nature take its course--then your harvest may be drastically reduced, if not non-existent. Here, we provide a few helpful tips on how to ensure you get that harvest, wherever you are.


Outdoor tutorial: force-flowering

Why should you force-flower cannabis?

Force-flowering cannabis is one simple way to ensure that your outdoor or greenhouse crop begins to flower with enough time to complete its growth cycle before the winter cold sets in and sunlight becomes weak and limited in duration.

In the northern, cold-temperate zones of the northern hemisphere (and the corresponding southern zones in the southern hemisphere), the time between hours of daylight dropping low enough for flowering to begin and winter frost setting in can be insufficient for flowering to complete; thus, artificially reducing hours of daylight prematurely can supply the extra short days needed to achieve harvest.

Force-flowering can also be useful for growers in more favourable climates who wish to produce multiple crops per year (a “perpetual harvest”). Some growers are able to harvest two or more crops per year by strategically depriving plants of light.

For example, plants can be started in February or March; some can be harvested by June using light-deprivation techniques, while others can be left to flower naturally in late summer and be ready to harvest by mid to late autumn.

In cool climates, autumn temperatures may drop too low for flowering to complete without intervention (© james j8246)
In cool climates, autumn temperatures may drop too low for flowering to complete without intervention (© james j8246)

For truly perpetual harvests, a few plants can be induced to flower every week or two (once they have undergone sufficient vegetative growth) so that harvests are similarly staggered.

When to force-flower cannabis?

Your window of opportunity when attempting to force-flower cannabis outdoors depends greatly on your location. In warm-temperate and tropical regions, there may only be a very short period each year in which cannabis cannot be grown, so ensuring that flower cycles end before that cold or wet season sets in is the only real requirement.

In cool-temperate climates such as the UK and the Netherlands, autumn conditions usually become too cold and damp to sustain healthy flower growth by late September to mid-October (although there are reports of outdoor crops flourishing until late November or even early December in some areas, as seasonal climate patterns shift and winters become milder).

Thus, to ensure that your crop finishes in time, it is advisable to commence light-deprivation in mid to late July, depending on the flowering time of the strain.

Naturally, your plants may not begin to flower until September, which can be a wet and windy month in many parts of the UK. In some cases, it may be advisable to commence force-flowering in mid-June or early July, which should provide your plants with enough time to grow vegetatively and complete flowering too.

Starting plants indoors is always advisable, particularly in regions that experience cool springtime temperatures.

How to force-flower cannabis?

Depending on various factors such as the size and number of plants, whether you are growing fully outdoors or in a greenhouse, and how much you are prepared to spend on your set-up, there are several ways to go about depriving your cannabis plants of light.

The basic concept is to cover your plants with material that cannot be penetrated by light, but that allows fresh air to circulate around. In some cases, use of fans may be advisable if possible, in order to ensure that airflow is sufficient.

Large greenhouses may be equipped with automated curtain systems which block out all light in moments (© umass.edu)
Large greenhouses may be equipped with automated curtain systems which block out all light in moments (© umass.edu)

If you are simply growing a few plants on your balcony or back garden, you can cheaply and easily construct lightweight frames from wooden poles and cover them with opaque, preferably breathable material; these frames can then be placed over the plants every night so that they are sure to get twelve hours of darkness each night.

Lightproof “sensory” tents designed for children with autism and related conditions are also commercially available for relatively low prices, and can be adapted into covers for your plants.

breathable blackout fabrics
This four-layer breathable blackout material is expensive but highly effective

For growers conducting larger-scale or greenhouse grows, different methods may be required. Outdoor growers may place their plants in sheds to block out light prior to natural nightfall (if you think you will need to move your outdoor plants at night to supply them with sufficient light, you will need to grow them in portable containers rather than directly in open soil) and greenhouse growers may use blackout curtains that can be drawn in a matter of seconds and protect an entire crop.

Other things to consider when force-flowering

Of course, once natural hours of darkness have increased to twelve hours or more per night, the need to cover your plants disappears and they can be left to the elements. You may wish to continue covering your plants if your crop is affected by light pollution (such as by streetlights), or if unexpectedly cold temperatures or windy conditions necessitate some protection against the elements.

Another thing to bear in mind is that if you begin force-flowering, it is crucial to stick to the lighting regime and not miss even a single day, so that plants are not confused into reverting back to vegetative growth. If budget allows, investing in automation schemes may be a possibility.

Lightproof sensory tents can be adapted to make covers for plants
Lightproof sensory tents can be adapted to make covers for plants

If you time it right, force-flowering cannabis can not only make the difference between a successful or failed harvest, but should also allow for increased yields.

In cool climates, the difference in temperature and light intensity between late summer and early autumn (when plants naturally begin to flower) and early- to mid-summer (when your plants will flower if forced to) can be so great that your buds will be noticeably larger, tighter and more resinous if grown under a force-flowering regime.

 

Comment Section

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Jorge

Thanks for the tipe on outdoor it never gets that cold out here in the AZ.

20/04/2015

Shelley brasington

I'm disappointed I cant get my question answered they just keep sending me all over the fucking internet. My question is what are safe coverings to use for the 12/12 lighting system for my outdoor plants

23/06/2016

Scarlet Palmer

Hello Shelley,

Thank you for your comment ? Unfortunately we cannot respond to grow questions on the blog, but we do have the Sensi Seeds Forum where you can ask a thriving community of gardening fans for advice, share your experiences, and see if your question has already been covered.

Also this quote from the post: "Lightproof "sensory" tents designed for children with autism and related conditions are also commercially available for relatively low prices, and can be adapted into covers for your plants" may point you in the right direction. I hope this helps.

With best wishes

Scarlet

24/06/2016

Cherookee

I think that the main problem is to understand your question.I read just the german translation of your question and their is no thens.

23/03/2017

G glue

Black Road felt works ex

09/07/2017

Glenn

I'm growing 3 in greenhouse I need to force them how many day do I do this for 1 week 2 weeks

07/07/2016

john

glen
you must learn about the type of plant you are growing.if yours are 8 weeks in flower you must cover and uncover for the full 8 weeks.

13/07/2016

Who can tell me. what kind fertilizer to use force cannabis to flower soon?

Help me please. Write down the name of fertilizer to force cannabis flower early...

19/02/2017

Scarlet Palmer

Hi there,

Thank you for your comment 🙂 Unfortunately, for legal reasons we cannot respond to grow questions on the blog, but we do have the Sensi Seeds Forum where you can ask a thriving community of gardening fans for advice, share your experiences, and see if your question has already been covered. I hope this helps.

With best wishes

Scarlet

20/02/2017

Nevigo

Fertilizer has nothing to do with your plants flowering.Its how many hours they get light that count.When you want to flower them, give them 12 hours of light, and 12 hours of uninterupted darknes.

19/03/2017

Joe

Flowering in summer is not a good idea as the high temps will cause your buds to be light and airy! Also they won't be as potent and may cause foxtailing

01/08/2017

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