Do Marijuana Seeds Need Light To Germinate

A step-by-step guide for successful cannabis germination grounded in science. Reviews strategies for germinating cannabis seeds and offers tips for success. We often get beginning growers in the store looking for seed starting advice. This blog will help you set up the right environment to germinate seeds.

Germinating Cannabis Seeds – A Step by Step Guide

Germinating cannabis seeds is one of the most exciting parts of the whole grow. It is almost magical to summon new life from a dormant seed; however, it can be very frustrating when things don’t go well. In this article, I explain how to germinate cannabis seeds successfully. I begin by reviewing the science of germinating cannabis seeds. I then describe several common cannabis germination strategies and share some cannabis germination tips and tricks. At the end of the article, I provide my step-by-step guide to germinating cannabis seeds. Be sure to watch my Germination Tutorial on YouTube!

Germination will always be exciting, but it does not need to be intimidating. There are many ways to germinate cannabis seeds successfully. Understanding the science and the shifting needs of the developing plant will allow you to choose the germination strategy that is right for you.

The Science of Germinating Cannabis Seeds

Cannabis seeds are among the easier seeds to germinate. They are large dicotyledon seeds that store a reasonable amount of energy for early life. Furthermore, cannabis seeds do not have any significant seed dormancy factors to overcome. If they are viable seeds they will germinate easily when exposed to the correct conditions.

Seeds become Sprouts During Germination

This may sound obvious, but it is important to consider because seeds and sprouts are different. When the cannabis seed is still a seed, it is resilient and does not depend on ideal conditions to survive. However, sprouts are different. As soon as the seed cracks open and exposes the radicle (tip of the root) it becomes a sprout. As a sprout, it becomes much more sensitive to external conditions. Whereas the seed only needs warmth and moisture to germinate; the radicle on a sprout needs warmth, moisture, oxygen, and darkness to survive and grow.

Germination Stage 1: Imbibition

The seed’s journey to planthood begins by getting wet which starts the process of imbibition. Imbibition is similar to rehydration. When wet, the testa or seed coat of cannabis seeds imbibe water which causes them to swell and soften. The force of water entering the cells in the testa physically ruptures the seed coat and allows the radicle (root tip) to escape. The imbibition of water also activates the metabolic activity within the seed protoplasm.

Warmth is Required for Metabolic Activity

The metabolic activity within the seed will only activate if the temperature is in the appropriate range. Like other seeds, cannabis seeds will not successfully germinate if the temperature is too low or too high. Room temperature is warm enough to allow germination, but warmer temperatures enable more metabolic activity and faster germination. The ideal temperature range to germinate cannabis seeds is 80-86 F (27-30 C).

Germination Stage 2: Respiration

Seeds carry stored energy to help power metabolic activity and growth until the plant can begin photosynthesis. However, just like humans and other animals, plants must engage in respiration in order to convert that stored energy into active energy that the plant can use. During the earliest stages of metabolic activity as the seed awakens from dormancy, the respiration is anaerobic or without oxygen. However, the sprout needs to quickly begin using oxygen in aerobic respiration to continue to survive and grow.

As metabolic activity resumes, the sprout will begin to grow. Cannabis seeds store most of their energy in their cotyledons in the form of starches and proteins. The plant uses energy from aerobic respiration to digest these starches and proteins into simple sugars and amino acids, which it mobilizes to grow the radicle (root tip) and hypocotyl (stem).

Cannabis Sprouts need access to both water and air

Seeds can be completely submerged in water during the first part of imbibition. However, if they are completely submerged after the radicle is exposed then the sprout will die from lack of oxygen. As soon as the seed cracks open and exposes the radicle it needs to have access to oxygen for aerobic respiration. This means that it needs some contact with air. However, it also needs continuous contact with water. To achieve the best results in the sprout and seedling stages it is best to use a grow media that will trap both air and water. As I explain below, paper towels work well for this during the early sprout stage and germination media like Jiffy Pellets or Rockwool cubes are perfect for young seedlings.

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Germination Stage 3: Orientation

At this stage of germination, the plant must orient itself to grow properly. The radicle must push down into the soil or media and the hypocotyl must push the cotyledons (first leaves) up out of the soil or media. Both gravity and light help orient the plant to grow in the proper direction.

Apply Light but Keep the Radicle in the Dark

Cannabis seeds do not require darkness to germinate. However, the radicle is sensitive to light. Bright light will stunt the radicle and can lead to a failed germination. When seeds are germinated in paper towels it is best to keep the sprout in total darkness until the radicle is about half an inch long (about 1.25cm). However, as the cotyledons emerge from the seed casing, they will be looking for light to indicate the direction they need to grow. Therefore, when the radicle is longer than half an inch it should be placed in media which will protect it from light. Once the radicle is safely in the media, light should be applied to the top of the media to signal the direction of growth for the cotyledons.

Germination Stage 4: Photosynthesis

During the germination stage the plant relies exclusively on stored energy from the seed. This energy is limited, so the plant must quickly begin producing its own energy through photosynthesis. The young plant works to establish its radicle in the media and push the cotyledons up into the light to begin photosynthesis. Once the cotyledons open and receive light, the plant will begin photosynthesis. At this point, germination is complete, and the plant can start producing its own sugars, starches, proteins and fats.

Nutrients for Germinating Cannabis Seeds

The nutrients and supplements that we provide to our plants are not their food. Nutrients and supplements support photosynthesis. Therefore, they are not needed until the plant has begun photosynthesizing. Indeed, adding nutrients to the water used for imbibition can actually inhibit germination. It is best to use plain water at a neutral pH (7.0) to imbibe the seeds.

Once the cotyledons are open, the plant can use very small doses of nutrients. However, it is easy to overdo it and burn the plant. When and how to begin fertilization depends largely on the media that you are growing in. If you are growing in coco or other inert and unamended media, be sure to read “How to grow cannabis seedlings in coco coir”.

Cannabis Germination Strategies

There are many viable ways to germinate cannabis seeds. Different germination strategies may be more suitable for different growers. Therefore, before explaining my step-by-step guide to germinating cannabis seeds, I will review some of the more popular germination strategies.

Soaking Seeds

Many growers begin germination by soaking seeds in water. This allows for faster imbibition of the seed because it is surrounded by water. It is a safe strategy to follow as long as you remove the seeds from the water before the seed actually cracks open. If you soak seeds, you should use plain (low EC) water with a neutral pH (7.0). Filtered or distilled water is best.

The Paper Towel Method

This seems like a make-shift hack, but wet paper towels provide an excellent air/water ratio for germinating seeds. They also allow you to precisely control the temperature of the seed/sprout during germination. As a result, using paper towels can speed the germination process considerably.

The paper towels should be fully saturated with water, but not dripping wet. I like to fold the paper towel so that there are two layers below and above the seed. You can then place the paper towels in an air-tight container to prevent them from drying out. I use pyrex containers. If you use a plastic bag, just make sure that you trap some air in the bag (don’t squeeze all the air out). The radicle does need some air, but there will be plenty, even in a sealed container. Place the sealed container someplace warm and cover it to protect the radicle from light.

The main drawback to the paper towel method is that it is possible to damage the young sprout when you transfer it to media. There are some easy practices to mitigate this risk. First, use cheap, single-ply paper towels. This prevents the radicle from growing between the plies. Second, place only one seed on each paper towel. This allows you to pick up the whole paper towel and avoid touching the sprout when you transplant to media. Finally, don’t keep the seeds in paper towels for too long. Once the root has grown to about 0.5in or 1.25cm, it is time to transplant it to media.

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How We Germinate Seeds Indoors

We often get beginning growers in the store looking for seed starting advice. To germinate seeds, or take them from dormancy to sprouting, you need to set up the environmental triggers to assist the seed. There are many different techniques for germinating seeds, and a lot of products and advice out there for how to get started if you’ve never done it. So much advice, that it can be very confusing. The following is a little advice for what we have found that works for a wide variety of seeds for flowers, vegetables, herbs, and even cuttings/clones:


When is the best time to start your seeds? If you are going to be growing your plants indoors, then anytime you’re ready is the best time. If you will be transplanting to an outdoor space, then it depends on the weather where you live. Check with The Farmer’s Almanac, or the back of the seed package will usually tell you how many weeks before the expected last frost date for your area to plant. Don’t know the last frost date for your region? This is a good page to help you figure that out.

Getting Your Seeds Planted

Always wear a mask when working with perlite!

Always wear a mask when working with perlite! Perlite is a form of obsidian characterized by spherlulites formed by cracking of the volcanic glass during cooling, used as insulation or in plant growth media. It is like tiny shards of glass and is very dangerous to your lungs if it’s inhaled.

Step one: Coco coir comes in a dehydrated brick. I hydrate the coir according to the package directions. Before doing this you would benefit from reading the notes in the Watering section of this post.

Step two: I mix perlite into the coir at a ratio of one-part perlite to two parts coir. The coir in our mixture holds moisture without staying too wet. The perlite helps aerate and loosen the media for water to drain easily while also retaining moisture. To keep the dust down, we recommend using water from a spray bottle to wet the perlite prior to handling. I stress again to wear your dust mask when handling perlite.

Step three: I have found that using a product with mycorrhizae increases germination rate and root growth rate after the seed sprouts. I mix the package-recommended amount on whichever product I am currently using.

Step four: Fill the seed tray with media and plant your seeds! Tip: A general rule for seeds is to plant them no deeper than one to two times the diameter of the seed. For very tiny seeds (i.e. lettuce) I simply drop a few seeds on the surface of the media and leave them uncovered.

Seeds respond to warmth and need heat to germinate. If your media, or the water you’re using, is too cold, the seeds will stay in their dormant state. Most cool weather plants or plants that do best in spring and autumn (i.e. spinach, kale, etc.) generally need temperatures between 45°F and 70°F to germinate. Seeds that require warmer weather (i.e. tomatoes and zucchini) will germinate better generally between 65°F and 90°F. Most seeds have about a 25-degree range in which germination will be activated in the seed. This is great for us beginners trying out lots of plants for the yard. If your room is cool, and you’re trying to germinate seeds, pick up an agriculture heat mat and thermostat from your local hydroponics store to dial in the ideal temperature.


Our seedling/clone rack at the Lush Lighting Hydroponic Store

The light requirement of seeds is a tricky subject. Some seeds do not require light to germinate (mushrooms), some do. There is a ton of scientific research available about this if you’re interested in learning about the phytochrome system in seeds. If you would rather just grow the plant what do you do? My advice: Use a light. Here’s why: All sprouts need light. As soon as that sprout emerges from the media it needs light; even if it didn’t need light to germinate. A seed that needs darkness, planted at the right depth, will be far enough under your media and will be shaded from the light for germination. In the store, we use a Lush Lighting Herbal Vador LED grow light hung beneath a shelf. Others have used CFL’s which are widely available (we also have CFL’s available in the store). Some others have had great success placing their seed tray in front of a south-facing window.

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A few notes about water:

  • Seeds like to be kept moist, and they don’t like to be immersed in water for too long. If seeds stay too wet for too long they will rot. If seeds stay too dry for too long they will dry out and die.
  • Doing a pH test on your water is a really good idea. When water pH is too high or too low, your seeds will not germinate. Most seeds germinate between pH levels 5.8 and 7.0. Matt Johnson wrote an excellent explanation of the importance of checking water pH.
  • Water quality can make a big difference in your success rate. If you live with city water consider using RO filtered, or bottled distilled water (READ LABELS! You might be really surprised at some of the stuff that is in bottled water being sold on store shelves!). City water has been treated with all kinds of chemicals to remove bacteria and the like. Some of those chemicals (i.e. chlorine) are not good for plants.
  • Water temperature matters. Cold water from a tap is often too cold for germination. Use water within the best temperature range for your plants. Leaving your water to sit out overnight to come to room temperature before you water your seeds is a good idea (Matt Johnson’s article –mentioned above—can give you more good reasons). The water we use to water all the plants here at the store has come to room temperature before it goes on the plants, including the seeds.

How often do we water? Water as often as it takes to keep the media moist and not drenched. We use a variety of techniques to keep our seeds happy: a mister, bottom-watering container, and/or a humidity dome.

The mister has a gentle mist that does not “skate” the tiny seeds (like lettuce) across the top of the media. It’s very important to make sure your seeds stay where you initially place them.

Another watering technique we use is bottom-watering. Put about ¼” of water in the bottom tray for your media to wick up. This technique is very helpful if your media is drying out too fast. If your growing room is dry, bottom-watering combined with a humidity dome may be a good option for you. If you need to step away from watering for a few days, it will retain the moisture for the seeds and keep any small sprouts from drying out. Small plants generally do well with a humidity level around 60%.

Be patient! Sprouts will come in due time!

How Long Will It Take before I see something happening?

A common question with an answer most of us don’t want to hear… it depends. I will say, the highest success rates come from recreating each particular seed’s ideal germination environment. Most seed packages will give you a time range anywhere from a few days to a few weeks. All seeds are a little different, even the same packet of seeds can have some that sprout quicker than others. Be patient, monitor your temperature and moisture and then you will be rewarded greatly when those first seeds germinate and those little sprouts emerge. It’s exciting to watch those small seeds become large plants. Happy Gardening!

About Matt Johnson

Matt is the President and Founder of Lush Lighting, Inc. He is a leader, a visionary, a mentor, and caring family man. Matt openly shares his wisdom, generosity and assistance with everyone he encounters. He is a sharp business man, admirable, loyal, and willing to step out of the box to make things happen. Whenever he gets a chance, he squeezes in a round of golf or a movie with his wife.


If you want to check more on different techniques for germinating seeds, we can share to you our hidden steps.