What’s the Ideal Light Schedule for Seedlings?

What is the Ideal Light Schedule for Seedlings

Weed can be grown in two major ways – you can either choose to grow it outdoors, under the sky and at the mercy of the sun, or you can choose to grow it indoors. Growing your marijuana indoors allows you to exert a much greater level of control over the growth of your plants as compared to the outdoor growth, which largely depends on natural factors upon which you have limited control – light being the most important. In this article, we take a closer look at the ideal light schedule for seedlings of the marijuana plant.

In addition to that, we also take a closer look at grow lights and why they are important, as well as the various phases of growth that a marijuana plant goes through. These are some things which are really essential for a grower to understand because it is based on the growth phase and the type of grow light that they are using, they can decide the ideal light schedule for their seedlings! We will also take a detailed look at the seedling phase of growth and then give some insights on the three best grow lights for seedlings. 

Let us take a closer look:

The Importance of Grow Lights

When you grow weed outdoors, it gets all the essential elements of growth (water, air, heat and sunlight) from the nature. The sun is the most important object for the outdoor growth of weed because it is the source of both, warmth as well as light which are critical for the growth of the plant. It is with the help of the light of the sun that the marijuana plant performs photosynthesis, which is a chemical reaction where the plant converts sunlight into energy. It is also towards the direction of the sunlight that the plant grows. 

Furthermore, sunlight also helps plants in the process of metabolism and helps with the generation of chlorophyll and other pigments and chemicals. In the case of weed, that would also include THC, which is the primary component that gives you the effect of being ‘high’ upon smoking weed. Hence light is critical.

Coming to grow lights now, they come into the picture when you grow your weed indoors. Growing it indoors is better than the outdoor growth because it ensures that even on days when the sun is not there due to the clouds, or when there is heavy rain or snow, your plants are not damaged because you are providing them with an artificial source of light: grow lights. Basically, grow lights emulate the natural light of the sun and hence are very important for the growth of marijuana plants.

Let us now take a closer look at the various growth phases of the marijuana plant.

Understanding the Various Growth Phases of a Marijuana Plant 

Different people tend to categorize the growth phases differently. However, we consider that there are seven phases of growth in the marijuana growth cycle. 

  • Seed: This is the first phase of growth where the seeds are sorted. It is the female seed which is capable of budding (bud being the end product that you smoke). Male plants do not produce flowers and often cause a deterrence to normal growth.
  • Germination: Then comes the germination phase where seeds are soaked and kept in a moist, warm and dark place till they begin to sprout small roots. The germinated seeds are then planted on to mud where they are planted with the root facing downwards.
  • Seedling: The seedling phase of growth is one where the shoot sprouts upwards towards the direction of the sun and the first leaves begin to emerge. This is a very delicate stage and extensive attention needs to be paid here as this is the ‘make or break’ stage of the plant’s growth cycle.
  • Vegetative Growth: As more leaves begin to sprout, the marijuana plant’s height begins to grow and the shoot starts turning into a thicker, harder and sturdier stem which supports the entire plant really well. This is a phase of rapid growth.
  • Pre-Flower: This is the phase just before the flowering/budding phase where buds begin to emerge and this is also the time that male plants (if any) must be separated because if their pollen gets released, it might result in the female plants getting damaged!
  • Flowering: This is the stage where the lights are dimmed compared to the previous stages of growth and the flowers begin to appear. This is also the phase which requires nutritional attention from the growers as the plant then needs to be provided with potassium and phosphorus-based nutrients. Pistils will begin to emerge after that and then you know that you are ready for harvesting!
  • Harvesting: This is the final stage in the growth cycle of the marijuana plant where you harvest the bud and then hang it to dry for four to six days following which your weed is ready to be smoked! 

Ideal Light Schedule for Seedlings

Now that you know which are the different stages of growth of a marijuana plant, let us take a closer look at the ideal light schedule for seedlings. Seedlings require special attention and care from the growers because they are the most delicate phase of them all. It takes quite some time for a plant to grow from the seedling stage to the vegetative stage and anything that goes wrong at the seedling stage is going to reflect in the later stages – and in a worst-case scenario, it can simply kill off the plant right there. Hence, extreme caution is advised.

Coming straight to the light schedule for seedlings, one needs to know that this is the phase of growth which requires the highest amount of light. Up to 18 hours of light are common for a marijuana plant which is in a seedling stage. The method of growing these seedlings is known as the 18/6 method, which represents 18 hours of uninterrupted light and 6 hours of uninterrupted darkness. 

This period requires a high amount of light because this is the time when the plant is developing from a seed to a plant – hence, the more energy it generates, the better it can grow and the stronger it can grow. While new leaves are shooting out during this time, the plant’s energy requirement is quite high and hence extensive period of light allows it to generate enough chlorophyll and perform photosynthesis for longer hours for a proper metabolism to happen. 

Interestingly, some people also tend to prefer the 24/0 method, where they provide the plant with 24 hours of uninterrupted light and 0 hours of darkness for a really long time and then they switch to 18/6 phase just before the plant enters the vegetative stage. However, we strongly recommend growers (and particularly novice growers) to follow only the 18/6 method as darkness is equally important for the plant as too much light can result in the generation of too much energy which can actually wear out the plant and have a negative impact on its growth. 

Frequently Asked Questions (FAQs) regarding Ideal Light Schedule for Seedlings

  • How much light is too much light?

When it comes to the seedling phase, many people believe that there is nothing such as ‘too much light’. Technically speaking, light begins to become a problem for the plant when it is approaching the pre-flowering/flowering stage because you can’t flower a marijuana plant without giving it at least a 12-hour darkness/12-hour light treatment. However, we believe that using the 18/6 method is an optimal way to grow your marijuana plants in the seedling phase. 24 hours of light is too much light.

  • Do seedlings require darkness?

Yes, seedlings, like all phases of the marijuana plant’s phase require darkness. However, they require the least darkness. While flowering phase requires you to have as many as 12 hours of darkness, seedlings can do with minimal darkness (most growers prefer 6 hours but some provide 24 hours of light too). However, dark hours are required so that the plant doesn’t burn out due to excessive metabolism.

  • How far should the light be from the seedlings?

Under ideal circumstances, you should begin with about 18” above the soil and then as the seedling begins to grow, you can lower it a little, but not too much that it actually burns out the plant! Seedlings require a lot of light but they are also very delicate and can easily burn from excessively intense light. We recommend that you keep your lights at an average height of 15”-20” away from the top of seedling at all times if you are using an LED light T5/Fluorescent lights can be kept about 6-8” away. Another important thing to note is that during this phase the circulation of air needs to be very well so that all the heat is dissipated but the warmth stays.

  • Which is the best type of grow light for seedlings?

LED lights are the best type of grow lights when it comes to the seedling stage of the marijuana plant. In fact, these are the best lights for all stages of the marijuana growth cycle. This is because LED lights offer a large range of wavelength spectrum and are also great when it comes to saving on costs pertaining to electric consumption. Moreover, they last for up to 50,000 hours and don’t even heat up that easily. 


We hope this article helped you understand the various growth cycles of the marijuana plant, and particularly the seedling phase. When your weed plant is in the seedling stage, it requires the maximum care and attention, as well as has the maximum need for light because this is the phase where it grows from being a seed to being a plant and has a high-energy requirement. 

To conclude, the 18/6 method of growing your weed is the best way to do so, where you provide 18 hours of uninterrupted light and 6 hours of uninterrupted darkness as it produces adequate energy as well as allows the plants to ‘rest’ for a while before another metabolic cycle begins! We hope this helped you grow your weed better.

Happy Smoking! 


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