Understanding Light Cycles in Hydroponics

Understanding light cycles in hydroponics are necessary if your plants are to derive all that they can from the nutrition you give them. Many hydroponic growers need help knowing how long to leave their grow lights on. Some tend to want to keep their lights on 24 hours a day, believing that this constant exposure will be better for their plants.

Let’s look at what’s going on in the plants themselves. Let’s also remember that, in any hydroponic setup, the aim is to emulate the conditions found in nature as much as possible and provide that to optimum effect.

All plants thrive in an outdoor environment where the cycle is of successive light and dark periods. It is that cycle that hydroponic growers should try to emulate to the best effect.

What is a Light Cycle?

As it applies to plants, a light cycle is the alternating light and dark cycle that plants receive daily. The duration of this light and dark determines how a plant will grow and whether it will flower (if it is of a flowering variety). Different types of plants have their preferred light cycles, and these cycles vary in the different seasons of the year.

In nature and outdoors, plants experience a daily cycle of light and dark and an annual or yearly cycle where the relative proportions of light and dark hours change according to the seasons.

In the winter months, plants have long dark and relatively shorter light periods—the time spent in light increases when spring approaches, while the dark hours decrease in number. The light hours reach their maximum during the summer, while the dark hours are at their minimum.

Then as autumn starts getting itself into gear, this pattern changes again and begins to reverse, with the dark hours being much more numerous than the light hours in the middle of winter. This process is one of several ways your plants will benefit from growers understanding light cycles in hydroponics.

It is from this regulated change in the duration of light and dark, as differentiated by the constantly altering light and dark proportions of the different seasons that plants’ flowering behaviour derives.

Mimicking a Daily Light Cycle

In a hydroponic grow room or tent, we’re not suggesting growers emulate this vast sweep of the seasons, but they should seek to emulate the daily process that characterizes a day’s cycle.

Experienced growers may alter the daily cycle of light hours followed by dark hours to control their plants’ behaviour. A favoured process for vegetative plants is 18 hours in light and 6 hours in the dark, mimicking the normal light cycle of a summer’s day.

As plants become established in their vegetative stage, they will need lots of light for healthy growth. Leafy plants need an abundance of light in the blue and red frequencies of the colour spectrum. Growers can achieve this range by using full-spectrum LED grow lights.

In the outdoors, plants get 14 to 16 hours of light a day; about five of these hours contain quite intense sunlight at around midday, followed by several hours of darkness.

To imitate this in your grow room, aim to provide about 14 to 16 hours of artificially provided light, followed by 8 to 10 hours of the dark; this cycle will repeat daily.

The amount of darkness determines how a plant behaves. Plants must develop to their vegetative stage, followed by their flowering stage. An electric timer is a straightforward way to automatically switch your lights on and off according to the schedule.

There are Different Requirements for Different Plants

A timer is handy when growing several different plant types, as some plants prefer different light and dark cycles. So if there’s a combination of plants, you’ll have to plan your timing schedule according to your various plants’ needs. An electronic timer should take the effort out of this for you.

Light Cycle for Long Day Plants

Plants that prefer a “long day” need 18 hours of artificial light daily. Such plants include lettuce, wheat, spinach, potatoes and turnips, all plants that flower in the summer; therefore, they prefer the long day cycle.

Light Cycle for Short-Day Plants

Plants that prefer to have a “short day” need fewer than 12 hours of sunshine daily. These include strawberries, chrysanthemums and cauliflower, and they need the dark hours in which they can photosynthesize to flower; anything less than 12 hours of darkness will cause them not to flower. These plants bloom in the spring months; therefore, they prefer the shorter day cycle.

Light Cycle for Non-Flowering Plants

These plants, because they produce no flowers, are the least fussy. No amount of light or dark will make them produce flowers or fruit, and they will not do so under natural conditions in any event. Such plants include corn, rice and roses.

While it is best to have the different light cycle plants in other parts of your grow room, there may be circumstances in which some growers will find this difficult, for example, if space is limited.

The grower must mix these differently cycled plants if this is the case. Working out a compromise halfway between the long and short day cycles is possible. About 14 hours of artificial light per day is comfortably in the middle.

From the above, you can see why it is inadvisable to keep the grow lights switched on for 24 hours continually. Doing so will confuse the plants considerably, throw out their flowering stages, and subvert the other less apparent stages of the plant’s growth cycle, which are, although unseen, necessary for the plants’ healthy growth.

Controlling Plants’ Growth Cycle at Vegetative and Flowering Stage

For plants which usually flower, there may be instances when you want to prevent them from flowering for as long as you can. It is certainly possible to stop the plants from flowering by keeping them at their vegetative stage indefinitely. The way to do that is by subjecting them to continually short darkness times, simulating a night less than 12 hours, depending on the plant species.

Some species of plant may be encouraged to flower by subjecting them to reduced hours of light and more hours of darkness, effectively tricking them into thinking that this is the time to come into bud and to blossom. Growers accomplish this by going from an 18-hour light and 6-hour darkness cycle to a 12-hour light and 12-hour darkness cycle.

Plants grown vegetatively will not need a dark period, so giving them 24 hours of continual light every day is possible. Growth rates would be faster, and the resulting crop would consist of bigger plants without any downside to doing this. Herbs will flourish in this way in conditions of continual light, as will lettuce and spinach.

However, plants grown specifically for flowering or to produce fruit will need several hours of darkness, forcing them to flower. This emphasis on night needs to be in force every day; the timer needs to switch your grow lights on at the same time each day and off again at the same time each day as the plants get used to this cycle which empowers them to blossom.

So there we have it. Hopefully, this article will have enlightened you about understanding light cycles in hydroponics. Light cycles should no longer be a mystery; you should choose the light cycle depending on your growing plant.

Read this in conjunction with our article on the best distance to have your lighting from plants, and you’ll learn the best practice on how to best treat your plants to the effects of your grow lights, and you’ll be well on your way to understanding the light cycles in hydroponics.