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Forced Darkness in your Garden: Turning Crops To The Dark Side Featured

Get the best and most efficient yield by controlling your plants’ photosynthesis period. Get the best and most efficient yield by controlling your plants’ photosynthesis period.

 

There’s an increasingly popular trend of tinkering with your plants’ photoperiod in order to trigger the flowering process out of season. The benefits are obvious: You get precocious amounts of flowers whenever you please and you get them more times per year than is possible using a natural light cycle.

However, this advanced method of growing offers some challenges based on your setup as well as the attention you can pay to your crop on a daily basis. Do you grow indoors or outdoors? How consistently can you stick to a schedule for your photoperiod? What kind of plants are you growing?

But before we get into those details, here’s a little bit of history about the harvest-on-demand technique known as...

FORCED DARKNESS

For at least the past 10,000 years, human beings have been farming. During almost that entire time, the fundamentals were the same: dirt, water and light. But as any grower knows, there’s a lot more you can pay attention to in order to maximize your yields.

Strangely, it wasn’t until about World War I that anyone noticed (or at least recorded) that plants respond to darkness just as much as they respond to light. In fact, given the right kind of plant, the response to darkness can be pretty dramatic.

He figured that since the day is shorter in winter, its blossoms might have to do with longer periods of darkness.

The same way that muscles respond to positive (work) stimulus such as lifting weights, and negative (rest) stimulus that happens during sleeping (where growth actually happens), so too do plants balance a cycle of stimulus and rest to produce big, juicy fruits.

In his book Reaching for the Sun: How Plants Work, author John King credits this discovery to JulienTournois, a doctoral student in Paris who first recorded the discovery of the forced darkness phenomena.

Tournois noticed that in winter his plants were blossoming like crazy. He figured that since the day is shorter in winter, its blossoms might have to do with longer periods of darkness.

Tournois took a scientific approach to testing his theory by screening out light for consistent periods of darkness. It worked like a charm. He even found that the most effective photoperiod was 18 hours of darkness and only six hours of light, at least for the plants he was testing at the time.

After testing his theories on both the Japanese hop and hemp plants, Tournois was convinced that it was “the length of the night, not so much the shortness of the day, that was the deciding factor in when his plants flowered.”

Sadly, Tournois died in service to his country during World War I, before he could figure out all the details. But his re-search was continued, most significantly by the United States Department of Agriculture. Working for the USDA, two botanists, W.W. Garner and H.A. Allard, published their findings in a paper titled “Experiment Station Record.”

Working mainly with tobacco and soybeans, but also with a variety of other plants, Garner and Allard confirmed Tournois’ theory that the photoperiod — the specific ratio of hours of light to hours of darkness — is indeed what determined the flowering in most plants. Therefore growers could control the flowering of their crop by artificially inducing periods of darkness.

As autumn approached and nights got longer with each passing sunset, it was guaranteed that their life cycle was coming to an end. That means it’s time to cash in and yield fruit.

This breakthrough led to the classification of plants according to photoperiod responses. Garner and Allard came up with three basic categories:

Long-day plants flower naturally when the photoperiod favors more hours of light than darkness.

Day-neutral plants can flower year-round, based on criteria other than photoperiod.

Short-day plants flower when the photoperiod favors more hours of dark than light.

As testing continued, researchers noticed something curious. It wasn’t the intensity of the light that made a difference in the plants’ flowering response. It was the consistency of the darkness.

This made evolutionary sense given the extremely reliable cycles of darkness throughout the year, more so than the less consistent intensity of light that can naturally vary from season to season. The Earth doesn’t randomly face the sun in the middle of the night. It spins at a steady rate of one rotation every 24 hours, steady as she goes. It has for eons.

Equally consistent is the length of night found during each season. Plants learned to identify the seasons changing. As autumn approached and nights got longer with each passing sunset, it was guaranteed that their life cycle was coming to an end. That means it’s time to cash in and yield fruit.

On the other hand, temporary periods of darkness are indicators of something more fleeting – cloudy weather, or a physical obstruction, rather than the change of the seasons. Plants aren’t so fickle as to give up their fruit for anything but their definite end. They’ve got to be sure. Once they are, the priority of the plant’s apical meristems (or growing tips) switches from producing leaves and stems, known to growers as the vegetative phase, to producing fruit, which is the flowering phase.

Armed with this knowledge, clever growers learned that they could artificially activate this natural process as long as they consistently created uninterrupted periods of darkness for their crops.

WHY USE FORCED DARKNESS?

The best reason to use forced darkness is for commercial purposes. If you sell a cash crop, like poinsettias for example, then it is a huge market advantage to be able to cause blooming on demand year-round. In fact, commercially, growers of poinsettias are famous for using forced darkness to stay ahead in the market.

Forced darkness also allows growers of high-value plants to be able to harvest more times per year than the competition. This way, you have the advantage of timing as well as volume. Imagine being able to supply a full shipment of product while your competitors are still dragging their feet through the veg phase.

THE IDEAL FORCED DARKNESS SETUP

Forced darkness can be used by almost all ingenious growers. However, because of the strict adherence required to mimic nature’s natural light cycle, outdoor greenhouse gardens are the best setup.

This might be surprising to indoor growers who have complete control over their lighting and plenty of mechanisms that easily deliver exact timing. However, the energy cost of maxing out your veg phase with 16 hours of daylight and then sticking to a down-to-the-minute schedule of darkness to trigger flowering can be the opposite of cost-effective if you’re not growing enough product.

Okay, so without further delay, here’s what you do:

Start by moving a heavily vegged plant into the greenhouse, and use whatever means possible to make sure that the greenhouse is dark for 12 uninterrupted hours or more per every 24 hours. Seriously, even a few minutes of light will undo all your effort.

With a fair amount of diligence, any grower can soon take control of their plants’ flowering period.

Tarps are the industry standard, but configuring how your tarps are drawn over the greenhouse is something to consider. There are companies out there like Harvest Excel that make automated canopy greenhouses. This takes the element of human error out of the equation because you set the canopy of your greenhouse on a timer and voilà, every 12 hours on the button, you have sufficient darkness in your greenhouse to trigger big ol’ flowers.

There’s also the option of manual labor. But that means you need a dedicated work staff that will pull those tarps exactly right, almost to the minute, every day, twice a day.

With a fair amount of diligence, any grower can soon take control of their plants’ flowering period. While we love the amazing crops that nature has given us, the most successful growers take control of their plants and use their natural proclivities to maximize their productivity.

© Copyright RosebudMag.com, 2013



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A killer rock song on the subject of light, if not photosynthesis.
Last modified on Thursday, 13 June 2013 23:46

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