Black Out Budding and Flowering Growing Outdoors

black out systems outdoor growing

Black Out Budding and Flowering Growing Outdoors

Black-Out System Basics

[quote]Blocking the light in the morning is usually better for your plants, so they don’t overheat when covered. Just find out when the sun is supposed to go down and remove the cover 10 hours prior and let them soak up the rays and transition naturally into darkness[/quote]

black out system greenhouse frame

Above: Poly Vent System is easily adapted to for Black Out  to induce off-season flowering and budding with sunlight.

If you grow short-day flowering plants outdoors you have to be patient.

And that’s because your favorite plants won’t start developing flowers until the the critical day length has been reached: usually about 12 hours or more of darkness is required.

For most of us, this is never soon enough.!

Depending on where you live in the world in terms of latitude is what creates the difference about when this would happen naturally. While some of us would just rather harvest sooner, unfortunately for some growers in Northern latitudes it usually means a very short window for the bloom/fruit/bud phase and severely limits what kind of varieties of short day flowering plants they can grow; if they can even grow them at all.


A Black Out system is the answer. From small scale and really inexpensive to grand scale and elaborate this is a great way to get your short-day plants flowering ahead of schedule-and ahead of your competition!


Simply put, a Black Out system forces earlier flowering by completely blocking the natural sunlight for a portion of the day, effectively tricking your crop into thinking it’s later in the season and making your plants shift into the bloom phase.


Because your plants need to be enclosed-in to accomplish this, there are going to be some important considerations you will need to address. For example, plants need to breathe or moulds and mildews can develop because of condensation. Think about it: those plants hold a lot of water, and youplan to enclose them to block light-where is all that water vapor going to go, especially when it’s still warm out?


The easiest, cheapest and possibly best example to illustrate how to operate a Black Out system to force early flowering is as follows. Note that it is a MANUAL approach, meaning someone has to be around to open and close the lid to shorten the photoperiod and to allow the right amount of light in for growth.


Site Selection-Anywhere that is out of the way and that you can carry water to easily is ideal. A balcony, back porch or terrace for example, would be a great place. A white reflective wall behind the can will potentially help to redirect more light into the opening when the lid is off. For good growth, your plant(s) should get about 5 hours of direct light. The most important part is the 12-14 hours of uninterrupted darkness however.

Variety Selection-You will want something that stays compact in growth and bloom and preferably a fast finisher. Stuff that finishes at around 6 weeks is perfect. Mould hardiness is a plus too. Stuff that hermies out (creates hermaphrodites) under stress easily should be avoided too if you want to grow seedless.


To speed up the time until plant shift into bloom and shorten the amount of time you will need to do this manual job daily and punctually allow your plants to receive ten hours of light daily. That means that either right before sunrise or ten hours after it you will need to be around.


Blocking the light in the morning is usually better for your plants, so they don’t overheat when covered. Just find out when the sun is supposed to go down and remove the cover 10 hours prior and let them soak up the rays and transition naturally into darkness


Late Sun blocking is trickier but works; plants may get hot. It also means more work because you will want to remove the lid again once its sufficiently dark out. Otherwise, plants become stifled or even sick without good air flow.


TIPS: Watch out for condensation; prune a few leaves if necessary. Also watch for light leaks or infiltration and interruptions from things like patio or security lights. Black is beautiful, so keep it that way for 14 hours straight and you can harvest earlier than under natural conditions.

greenhouse growing for black out systems freestanding house

 Freestanding house –  a stand alone greenhouse, AKA: tunnel; high tunnel; cold frame; hoop house; etc

greenhouse growing for black out systems gutter house

Gutter connect – a greenhouse range where roofs are linked together with shared gutters, AKA: multispan (poly), venlo (glass)


Our friends At Steele Greenhouse Components manufactrure and import a wide variety of cost effective solutions, including budget-minded customs.  Their M-Series and S-Series are featured above.  Engineered structures for less

About Erik Biksa 247 Articles
Erik Biksa has been writing about and discussing hydroponics growing, related technologies and cropping methods since 1999 in a variety of professional publications and platforms globally Erik has travelled the world learning and teaching modern growing techniques and technologies and is appreciated by many growers for his informative yet hands on approaches. Presently, he is the Editor at Grozine Hydroponics Mag.