Flower Forcing- How to Force Flowering in Your Plants

How to force flowering in your favorite plants

Whether you call it flower forcing, blooming, flowering, or photo-period manipulation, it is all the same thing. Some plants measure the dark periods and light periods of each day and change their growth patterns based on that information (i.e. switching from vegetative growth to flowering growth). You might remember your mother, grandmother, or aunt keeping a poinsettia in a dark closet or spare room around Christmas time. For most plants the trigger to grow flowers, fruit, and seed is based on the length of the dark period each day.

Taking Advantage of
Your Plant's Instincts

The biggest example is how plants will put their full energy into a reproductive effort in preparation for the coming winter. The plants know when to do this by measuring the amount of darkness in each day. The nights get longer and longer in late summer and heading into fall. At some point the plants instinctively know to begin their reproductive efforts. It is exactly this response to the dark period that will give you control over flower forcing.

Some plants are very particular. This is especially true with plant varieties that originate from around the equator. Many equatorial varieties require 12 1/2 or even 13 hours of uninterrupted darkness (each day) in order to force them into flowering properly. Most plants are less picky, and will begin flowering when they begin getting 12 hours of uninterrupted darkness every night (and always at the same time each night).


A Quick Word About
Duplicating Mother Nature

Use a digital timer to control your light/dark cycle properly

In order to do this, you need an area that you can keep pitch dark. If the plants were measuring the dark period with an hourglass, an interruption in the dark period would be like starting the hourglass over. Also, you will need a timer for your grow light. It is unlikely that you can duplicate the precise timing and regularity of the heavenly bodies of the universe every night and morning, everyday, for eight or ten weeks without a timer.

Plants have evolved to be highly in tune with these cosmic calendars. Give your plants anything less than universal regularity and you will have bad effects on the plants in your garden.


The Single Best Flower Forcing Tip

Personally, I would highly recommend a digital timer. They are the most reliable option. They don't have little pegs that physically turn your timer on and off (eventually wearing out and failing to turn your lights off). They are also more accurate. You timer should be grounded (three prong) where you plug your light in at the timer AND where the timer plugs into the wall.


Flower Forcing Goals

Place your light in the area you choose. Set the timer to turn your lights off for 12 hours, and then on for 12 hours. The light schedule you choose should be convenient for you, but also should help you with your goals in the garden. Namely...

  1. keeping light out during the dark period

  2. keeping the temperature down during the light period

Using a Thermometer to Fine Tune

A good indoor-outdoor thermometer will help you keep track of temperatures in TWO spots...your average grow room air temperature, and also your hot-spot!

It may be a little tricky at first trying to balance these two things, but a thermometer is a very useful tool that will help you figure it out. I use this kind here. It measures the air temp in the room wherever I place it, and it has a remote probe that I put in the hot spot of my garden.

It also remembers the minimum and maximum temperatures, which I check and reset every night to keep track of things from day to day. Once you have the garden area dark during the "dark period" and running at the correct temperature during the "light period", it is just a matter of waiting out the flowering period of your plants (and feeding them in the meanwhile, of course!).


Learn more about the Flowering Stage


Leave the flower forcing page and
Check out the Plant Life Cycle page

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(maintaining your hydroponic nutrient solution)


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