Cannabis seeds need only water, heat, and air to break dormancy and germinate; they do not need extra hormones, fertilizers, or additives. Seeds sprout How much light does a weed plant need? Discover the answers plus cannabis light schedule tips, how to choose the best lights, helpful FAQs, and more. Did your cannabis plant just die for no apparent reason? Frustrating, isn’t it? There is a whole range of reasons why this might have happened and in
Jorge’s Cannabis Encyclopedia: Seed Germination
Cannabis seeds need only water, heat, and air to break dormancy and germinate; they do not need extra hormones, fertilizers, or additives. Seeds sprout without light in a range of temperatures. Strong, viable, properly nurtured seeds germinate in 2 to 7 days. At germination, the outside protective shell of the seed splits, and a tiny, white sprout (radicle) pops out. This sprout is the root, or taproot. Cotyledon, or seed, leaves emerge on a stem from within the shell as they push upward in search of light.
Break dormancy: Put newly harvested seeds in the refrigerator for a week or two to simulate winter. Remove and germinate. Seeds will germinate more uniformly because they all come out of dormancy at the same time.
Timeline for Germinating Most Seeds:
At 36 to 96 hours – Water is absorbed, root tip (radicle) pops through outer shell and is visible.
At 10 to 14 days – First roots and root hairs become visible.
At 21 to 30 days – At least half of seeds are rooted by day 21. Seeds not rooted by day 30 will probably grow slowly.
Once seeds are rooted, cell growth accelerates; stem, foliage, and roots develop quickly. Seedlings develop into full vegetative growth within 4 to 6 weeks of germination.
Seeds are Prompted to Germinate By:
Water: Soaking seeds in water allows moisture to penetrate the protective seed shell within minutes. Once inside, moisture continues to wick in to activate the dominant hormones. In a few days, hormones activate and send enough signals to pro- duce an initial root tip. The white radicle (rootlet) emerges to bring a new plant into the world. Once a seed is moist, it must receive a constant flow of moisture to transport nutrients, hormones, and water so that it can carry on life processes. Some seeds need lots of moisture to wash out the dormancy hormones in the seed coat, and if they do not get enough moisture, they do not germinate. Conversely, too much water deprives the seed of oxygen, reducing its quality or destroying it. If fragile germinated seeds are allowed to suffer moisture stress now, seedling growth will be stunted. Soaking most seeds in water for 12 to 24 hours is all they need to initiate germination. All the nourishment for a seed’s initial growth requirement is pulled from the fleshy cotyledons, or seed leaves. Water seedlings with low-EC (electrical conductivity) household tap water during the first week or two of life. Supple- mental nutrients are unnecessary and if applied in excess can disrupt internal seed chemistry. Some gardeners prefer to germinate seeds using distilled or purified water that contains virtually no dissolved solids.
Temperature: Overall, cannabis seeds germinate in temperatures from 70°F–90°F (21°C–32°C) and grow best at 78°F (26°C). Temperatures below 70°F (21°C) and above 90°F (32°C) impair germination. Low temperatures delay germination. High temperatures upset seed chemistry causing poor germination. Seeds germinate best under the native conditions and temperature ranges where they were grown.
Air & Oxygen: Sow seeds twice as deep as the width of the seed. For example, 0.125-inch (3 mm) seeds should be planted 0.25 inches (6 mm) deep. Adequate oxygen is un- available for seeds planted too deeply, and tender seedlings have insufficient stored energy to drive through deep layers of soil or crusty hard soil when sprouting.
Agricultural Astrology — Planting by the Moon
Ancient Babylonians and Egyptians planted and harvested based on moon phases in relation to geographic location. The premise is that plants grow better when planted during the appropriate moon phase.
Moon phases cause ocean tides to rise and fall. They also affect the rise and fall of moisture in soil and fluids inside plants. The moon phase influence is said to be the same indoors, outdoors, and in greenhouse-grown cannabis.
Cannabis gardeners who plant by the moon report faster-sprouting seeds that grow into vigorous plants. However, scientific evidence is lacking in regard to cannabis and other plants’ relationship with agricultural astrology.
Seeds need oxygen from the air to germinate. Growing mediums that are too moist (soggy) will cut off oxygen supplies and the seeds will literally drown. Cannabis seeds germinate best when moisture is between 60 and 70 percent.
How much light does a weed plant need?
How much light does a weed plant need? A difficult question for many new growers. Light is one of the vital elements of all life forms, including weed plants, so you must get it right for your plants to thrive.
Keep reading as we unpack everything you need to know about cannabis lighting, from picking the best lights to optimum schedules. Let’s get started.
How much light does a weed plant need?
How you use grow lights determines the success of your marijuana plants. Answering the question, how much light does a weed plant need is complex. There are four lighting basics to master for the best results.
- Light intensity
- Type of light and placement
- Light spectrum
- Light schedule
Outdoors, the sun showers your plants in natural light, but indoors you’re in control of the cannabis light cycle.
Let’s take a closer look at each factor to consider.
Higher light intensity is generally associated with better growth. If you continue to increase the intensity of light that a plant receives, what happens? You might over-saturate your cannabis, which causes burns. However, your crops also risk stretching and stunted growth if you dim the lights too much.
Two common ways to measure light intensity are:
- Lumen — measures the light flow that a source emits. The higher the lumen, the brighter the light.
- Lux — measures the light intensity that reaches a plant’s surface.
Measurements of intensity
Growers typically use lux to measure intensity in their cannabis light schedule since plants only use the light that reaches its surface.
Here’s a simple table showing the best lux levels for two essential life stages:
|Vegetative||~15,000 lux||~40,000 lux||~70,000 lux|
|Flowering||~35,000 lux||~60,000 lux||~85,000 lux|
Choosing the right lights
Using specific marijuana grow lights for your weed allows you to maintain the plant’s health and progress to the next growing season.
The more plants you have, the more lights you’ll need for a successful marijuana light schedule. Average home growers use around one or two lights since most states permit no more than 12 plants.
To improve the growth and flowering of your plants, you may invest in an infrared grow light. It’s not necessary but works well with HID and LED lights.
Before you figure out how much light a weed plant needs, you must choose the right lights. HID (High-Intensity Discharge) lamps, such as MH and HPS bulbs, have a hood that reflects light.
Metal-halide lamps (MH) are ideal for the vegetative stage of the cannabis light schedule, while high-pressure sodium (HPS) lamps are perfect for flowering. Using both bulbs allows you to reap double the benefits.
Most HID lights display a particular hue compared to the best LED grow lights, which may show many colors. Using LED lights is a fairly new practice compared to traditional HID lamps. LEDs use lower wattage but provide the same quality light spectrum as HID’s.
Before starting your cannabis light schedule, pick the best lighting options for you. Here are some pros and cons of HID and LED bulbs to help you decide:
|Extremely bright, emitting up to 130,000 lumens||Need extra equipment like an electronic ballast and reflector|
|Efficacy rates of 150 lumens per watt||Emit an intense heat that may burn plants or spike room temperature|
|Relatively low maintenance||Degrade over time needing routine replacement|
|Lower outright cost||Power-hungry so higher electricity bills|
|Easy set up/beginner-friendly|
|Options for different marijuana lighting cycles|
|Energy-efficient/saves money in the long run||No industry standard for LED lights|
|Runs cooler than HID’s, so low risk of burn||Cheap models on the market may give inferior results|
|Mostly plug and go, no extra equipment||Potentially lower yields than HID|
|Streamlined—supports veg and flower phase|
|Can last up to ten years|
Distance from plants
Distance from the light can make or break your plants. Too close, and there’s a risk of light burn on weed, too far, and they won’t get the light they need. The optimum distance during your marijuana light schedule depends on the type of light and growing space.
During the seedling phase of the cannabis light schedule, grow lights should be kept around 24–36 inches away. Keeping an adequate distance prevents the seeds from drying out.
For the vegetative stage, lights should be 12–24 inches away. This phase of the cannabis light cycle requires more light for photosynthesis, so keeping them closer helps.
The light times for growing weed increase when flowering, and they should be kept around 16–36 inches away.
Here’s a handy guide for recommended distance depending on light wattage:
|Grow light wattage||Closest distance||Furthest distance|
|150W||5 inches||11 inches|
|250W||6 inches||13 inches|
|400W||8 inches||19 inches|
|600W||9 inches||25 inches|
|1000W||11 inches||31 inches|
Light spectrum for cannabis
Did you know the color of the lights influences your plants’ development? Different tones display certain hues based on the length of their waves. These varying shades suit the diverse stages, including a particular light spectrum for vegetative growth or the flowering phase.
The light spectrum for cannabis is the wavelengths between 380-750 nm. The colors represent the light wavelength. For example, if a light has a 400 nm wavelength, it appears purple to the human eye.
Light spectrum for seedling weed
During the seedling phase of your cannabis light schedule, use low-intensity light. Aim for 4000 lux—15% red, 30% blue, and white light.
Once your seedlings sprout their first leaves, you can double the intensity. When you spot more than two sets of leaves, it’s time for the vegetative stage.
Light spectrum for vegetative growth
For the vegetative stage of your marijuana light schedule, the main goals are root growth and tight internodes, so blue light is best. This shade stops your plants from growing too fast and developing long internodes, which causes light-blocking during flowering.
What is the best color spectrum for vegetative growth? For best results, use 27000 lux—100% blue light and less than 60% red.
Best light spectrum for flowering
In the flowering phase of the cannabis light cycle, your plants need more photons, so turn up the lux to 107,500—100% red while maintaining blue light at a lower level.
Excessive light increases your electricity bill and burns your plants.
Having a cannabis light schedule gives your flora a break. In the dark, your plants produce hormones that help them form buds.
Light and dark work together like yin and yang to form healthy greenery. How much light does a weed plant need? The answer depends on what stage the herb is in. Here’s a handy guide for the ideal light cycle for weed in different growth stages:
|How many weeks does this stage last||Lighting schedule|
|Seedlings||1–2 weeks||24 hours|
|Vegetative||3–5 weeks||18 hours on/ 6 hours off|
|Flowering||7–10 weeks||12 hours on/ 12 hours off|
Light cycle for seedling marijuana
Seedlings are babies—they need all the care and nourishment you can give. In this phase of the cannabis light schedule, feed them 24 hours of light. After 1–2 weeks, your seedlings will sprout leaves and be ready for vegetation.
Light cycle for vegetative weed
The vegetative phase is the stage where plants grow bigger and taller. They need long days and short nights. To prevent early flowering, ensure they get at least 13 hours of light in your marijuana light schedule. 18 light hours and 6 dark hours will encourage healthy and steady growth.
Light cycle for flowering cannabis
In the flowering phase, weed plants start forming buds. If they don’t get at least 12 hours of darkness, they may revert to the vegetative phase. During this stage of the cannabis light schedule, you must ensure that plants get absolutely no light during the dark times.
Optimizing lighting for maximum yield and minimal cost
Powering the grow room brightness can pull copious amounts of energy and cost you money. There are some ways to ensure you use lighting properly without going bankrupt. Here are some techniques to maintain the marijuana lighting cycles efficiently:
- Use lower wattage, LED, or energy-efficient bulbs
Energy-efficient bulbs tend to be pricey upfront but save you money in the long term. HID bulbs can use lots of power, whereas LEDs use less.
Reflective walls bounce light allowing you to make better use of your grow lights. To make walls reflective, you can use materials like mylar and plastic.
Nighttime tariffs are lower in many states, so you can save money by using grow room lights at night. Indoor growing gives you control of the cannabis light cycle, and using lights at night won’t make a difference. As long as you follow the cannabis light schedule, your plants will thrive.
Ventilation is just as important as marijuana lighting cycles, water, and nutrients. Adequate airflow helps maintain the proper humidity levels, temperature, and CO2 levels in the room.
The most efficient method is to have two ventilators opposite each other and the exhaust system on a different side of the room. This way, you’ll have a balanced atmosphere with stable humidity levels and temperature.
FAQ related to how much light does a weed plant need
To help you a little more, we’ve put together the most frequently asked questions on marijuana light schedules.
What types of bulbs are best during vegetative and flowering stages?
Metal-halide lamps (MH) are the best option for the vegetative stage, and high-pressure sodium (HPS) lamps are ideal for flowering. During different phases of the cannabis light schedule, bulb settings with different lux are used. Bulbs with lux 27,000 work for vegetative and lux 107,500 for flowering.
How many hours of light do marijuana plants need?
It depends on the stage that the plants are in. In the vegetative stage, they need 18 hours of light and 6 hours of darkness. During the flowering phase of the cannabis light cycle, weed plants need 12 hours of light and 12 hours of darkness.
Can you leave grow lights on 24 hours a day?
You can only leave grow lights on for 24 hours a day during the seedling stage. Seedlings need all the nurturing they can get, and more light helps them sprout faster. During this phase of the marijuana light schedule, low-intensity light helps seedlings grow.
How much sunlight does a weed plant need?
How much sunlight does a weed plant need? The more, the merrier. Cannabis plants need at least 10–12 hours of direct sunlight to thrive. They can still grow healthy with a minimum of 6 hours of daily sunlight, but you’ll get a smaller yield.
What is the best color spectrum for vegetative growth?
Blue light bulbs with 27,000 lux—100% blue light and less than 60% red are best during the vegetative stage. It works best because blue light produces chlorophyll—a chemical that helps plants grow stronger and move to the next stage.
If you continue to increase the intensity of light that a plant receives, what happens?
If you increase light gradually following the recommendations for the cannabis light schedule, then your plant will flourish. Increasing intensity outside of the guidelines can cause your weed to burn. Cannabis plants need the most intense light when flowering, and too much before that can be detrimental.
How much light does a weed plant need? Cannabis plants have different light needs depending on their stage. Seedlings need 24 hours, vegetative stage weed needs 18 hours, and flowering plants need 12 hours of light.
There are many factors to consider, such as color spectrum, light type, marijuana lighting cycles, and intensity. Remember, healthy plants start with quality seeds. Shop our selection at i49 of the finest weed seeds now.
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How to prevent the death of cannabis seeds and seedlings
Every grower, almost without exception, will have occasionally suffered the death of a plant during cultivation, just when it seemed that everything was going along nicely. In this article, we’ll focus on the main reasons why seeds may not germinate properly, or why seedlings may end up dead in the first weeks of life.
Seeds dying before germination
Cannabis seeds can die even before we start to grow them, in which case, when the grower comes to germinate them, they won’t open up and sprout at all.
The seeds of the cannabis plant, like many other types of seeds, must always be kept in the correct conditions, especially if you want to save the leftover seeds for later use and ensure that they germinate well in the future.
The same goes for unopened whole packs of seeds that have been purchased to store for later use. Sometimes, certain varieties are in high demand and there is limited stock, so the more astute growers will make sure they grab a few packs to keep in the vault until they find the time to germinate the cannabis seeds.
Cannabis seeds must be stored in the correct conditions
What to do with leftover seeds or unopened seed packs
Cannabis seeds need very low relative humidity and relatively low temperature for their proper storage, so the best plan is to keep them in a “no frost” refrigerator, in which both the humidity and temperature are maintained at very low levels for better conservation of food.
If we want to keep a seed package that’s still sealed, simply put the whole unopened pack into the fridge. The best place for its conservation is usually the small shelf where the eggs or butter are kept, although really any part of the fridge is ideal for storage.
If we want to save the leftover seeds from a pack for later use, we recommend storing them in the original Eppendorf tube or container used by the bank. In the original packaging, these Eppendorf tubes hold the seeds and usually also contain a few small silica gel balls, included to maintain very low humidity (10 to 20%) and help to ensure that the seed does not lose any germination viability.
If, however, we leave the seeds for a long period of time in any corner of the house it is possible that over time their viability to germinate will decrease, and when we plant them they may take a long time to germinate or indeed not germinate at all. it is also important to protect them from sunlight.
So if you wish to save the seeds in the best conditions, always keep them in the refrigerator, well protected from air, light and moisture.
How do we store leftover seeds to grow at a later date?
Death during the germination of cannabis seeds
Death during the germination of cannabis seeds is one of the most frequent failures suffered by every grower over the course of his or her cultivation career. There are several possible reasons that can lead to the seeds dying before they even open and begin to grow, which we’ll examine here.
Not all seeds have the same resistance to the errors that may occur during the germination process. Just as not all siblings are not all equal, neither are all seeds. By this, we mean that in the case of one seed germinating and the rest of them not doing so, it doesn’t necessarily mean that those that didn’t germinate were not strong or resistant, but simply that they were less so than the one that did germinate. If this occurs, we must ask ourselves why they did not germinate and look for any possible failings in the process.
Death by drowning the seed during germination
We start from the basic premise that the seeds require moisture, oxygen and a suitable temperature for germination; If one of the three aspects is not taken into account, it is quite likely that the seeds won’t end up germinating.
Putting the cannabis seeds in a glass of water and waiting 24 to 48 hours for their germination can be a fatal error for them. Re-hydrating the seeds in water is a good idea as long as they are not out of contact with the air for long, as they will be deprived of oxygen and most of the time they will end up dying; so if we use this method, we only leave them to re-to hydrate in water for a few minutes, although, preferably we will avoid any previous soaking or re-hydration (which in any case is not necessary).
We must maintain suitable levels of humidity for germination
The reason for this is that tap water contains chlorine, which sterilises the water to make it suitable for domestic use. However, this chlorine disappears by evaporation after a few hours, so if the water then gets contaminated, the seed can be attacked by any number of pathogens and eventually die. This example also illustrates why we must always touch the seeds with clean hands; If the seeds are handled with dirty fingers, it can lead a fungal or bacterial infection to contaminate them and severely compromise their development.
The same can happen in other germination media such as jiffy plugs, where the most common mistake is usually not draining away the excess water after re-hydrating the compressed peat. To this error, we can add that of burying the seed at more than twice its own depth, in which case it may not emerge despite having germinated perfectly well, but instead, simply end up rotting due to excess water and lack of oxygen. This error is also frequent in growers who germinate directly in the soil because when they first irrigate, the seed can be washed down into the soil resulting in them being buried too deeply, which makes it difficult for the seedling to reach the surface. It is always better to wet the substrate first, before sowing any seeds.
If you want to sow the seed directly into the soil and do it properly, when growing outdoors you must also act to prevent seed predators. Ants, birds, and many other animals or insects are another common cause of seed failure during germination. In the case of ants, they eat the small, delicate root, leaving the plant unable to develop and condemning it to imminent death.
Placing the seeds between moist serviettes/paper towels is one of the best germination methods for beginner growers. Since you can easily see if the seed has taken root or not. But we must also bear in mind that the germination medium, the kitchen paper, is made of cellulose, meaning it is an organic material that will decompose and rot, just like any product of this type.
Planting the germinated seed is also a crucial moment
It is, therefore, obligatory to change the napkins every day and a half, more or less, to avoid the seeds being contaminated by the pathogens that can appear as the napkins begin to rot. For this reason, we recommend placing the napkins in a deep plate and covering it with another one, leaving a small gap between the two so that air can enter, oxygenate the microclimate that is created during the germination of the seeds and avoiding them rotting.
Seeds dying due to lack of moisture
Just as excess water is one of the most common causes of germination problems, the lack of moisture is equally detrimental to the process.
If outdoor temperatures are around 20 to 24ºC, then we shouldn’t need do much more than start the seeds to germinate and wait for them to open, following the precautions already discussed. But in case of having warmer or cooler temperatures, we must act to raise or lower the environmental temperature for optimal germination, and find the best location for germination to be successful.
If it is winter, the plates holding the seeds are often placed on top of a low heat source to raise the temperature. We must, however, be careful: if this heat source emits hot air, the paper towels will dry out and the seeds will run out of moisture, affecting germination. If you realise this in time, you can re-hydrate the seeds and they will usually recover from and continue to germinate, although it is also possible that there will be consequences that may affect the subsequent development of the plant during its cultivation.
Not long after sowing the seed, we will see our little plant emerge from the soil
If we haven’t noticed soon enough that the seeds have been left without moisture, we can assume that they will have dried up completely, with their consequent death, and this is even more likely if the seeds had already opened up to show the root. This can also happen very easily if we germinate during summer when temperatures are high and humidity is usually very low compared to other times of the year.
Death of the plants during the growth period
The start of the growth period is a very important stage in a plant’s life, so several aspects must be taken into account so that it does not die of any of a number of causes.
One of the most frequent problems is root rot due to excess irrigation and lack of oxygen in the substrate. Up till now, this has been one of the most common causes of plant death during the growth period, especially with beginner gardeners who lack previous cultivation experience. In addition, the likelihood of this happening increases considerably in crops with auto-flowering varieties; we’ll explain what to do here.
When the plant emerges from the substrate, leaving behind its germination stage, it is crucial to take care with any excess water and the lack of humidity in its aerial parts such as leaves, stems and branches.
The proper conditions guarantee good germinación
When the plant is young and only has a very small root, its needs are few, it feeds and drinks very little. If we saturate the substrate with too much water, apart from halting the growth of the root (leading to little or no growth in the aerial parts), it creates the ideal conditions for the small roots to slowly rot. If the plant loses a part or all of its tiny root system in its first stage of life, it is almost guaranteed that it will die within a few days.
If we use a small 0.5L to 1L plant pot for the first part of vegetative growth, before transplanting them to a bigger pot, we will be covering our backs in case of any excess of irrigation, since the substrate will dry out again much faster than in larger pots. For this reason, this issue is very common for novice growers who are cultivating auto-flowering cannabis plants, where the use of 20L pots is recommended from the start.
It is often said that you must irrigate with an appropriate amount of water and nutrients for the size of the plant. As this is often complicated to carry out, as a rough guide we can irrigate the plants with an amount not more than 10 or 20% of the plant pot’s capacity. So, if they are 1L pots we will water from 100 to 200ml as long as it is not an auto-flowering plant.
If the plan is to grow automatic varieties, then during the first two weeks we water with 100 to 350ml per irrigation, every 1 or 2 days. Remember that the substrate must maintain a minimum of humidity to allow the plant to feed and continue to develop normally. If it is raining and the plants are outdoors, it’s a good idea to move or cover them, to prevent the substrate from getting soaked, which could easily lead to root zone problems.
The first stages of growth survived with success!
We hope that this information will be useful and help to stop your seeds and seedlings dying. Don’t hesitate to leave any comments or questions, we’ll be pleased to help.
The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.