marijuana seedling germinated in a peat pellet

The marijuana seedling stage is a delicate phase of the growth cycle, so it needs the right amount of care and planning to pull off properly. This might sound daunting or complicated for the beginner or amateur grower but cannabis seedling growth is not that complicated once you understand the basics of the whole process.

In this article, we will describe the entire process in detail and in the right order for you to get a clear understanding of steps to follow. We will cover topics like marijuana seedling light schedule, cannabis seedling growth, how to avoid damping off seedling problems, and more fundamentals. Let’s begin with the germination of your cannabis seedling.

When does the marijuana seedling stage start?

The cannabis seedling stage is exactly as the name suggests, it starts the moment your marijuana seeds have germinated. The marijuana seedling looks much like any other seedling, with two rounded cotyledon leaves that start off the photosynthesis process in order for the plant to start growing its first set of true leaves.

From time of germination till the first 3 to 4 sets of true leaves, the plant is seen as a seedling. Look at it as a newborn baby that needs just the right amount of light, air, water and nutrition to thrive and grow into a beautiful mature plant. We will go step-by-step into the cannabis seedling phase and look at the best practices for your marijuana seedling.

Cannabis grow stages from week 1 to 6 - Germination, seedling stage and early vegetative stage of a weed plant
Marijuana plant in seedling stage
A cannabis seedling with two rounded cotyledon leaves and a set of true leaves
Cannabis seedling with 4 sets of true leaves
By the end of the seedling stage, it will have had 3-4 sets of true leaves, and is ready for the vegetative stage

Choosing the correct pots and soil for your plants

The pot is the home in which your plant will live and thrive. So it is important to choose it correctly. There are a few different points to keep in mind when choosing the pot for your cannabis seeds. Here’s a quick breakdown for the most common scenarios.

Make sure you have drainage holes at the bottom of the pots. Churn the grow medium properly before planting for easier root penetration.

What are the best pots for growing cannabis seeds?

If you are planning to transplant your seedlings into larger pots for the actual growth and flowering, then specially made smaller seedling trays and pots may be the best idea for you. A lot of growers will germinate more seeds than they need in order to hedge their bets by observing the marijuana seedling growth in each plant. This way they can choose to take the healthiest of seedlings onwards to full maturation.

On the other hand, you may not want to transplant your seedling at all. This is true in the case of autoflower varieties. Most amateur or new growers can safely avoid the transplantation of their seedlings to the final pot in order to avoid any unwanted stress on their plants. So you can also choose to plant them directly into their final pots, which usually measure around 15 to 20 liters.

Photo-period plants might need a few transplantations in order to maximize growth in case the grower is so inclined, but it is still okay to just plant them into a large pot and then switch them to flowering when the plant is occupying about half the available space in your grow area.

What pots should you use for autoflower seeds?

Autoflower seeds have a very short lifecycle and are also known for being fairly touchy about dealing with any kind of stress. As a result, most growers will avoid transplanting them. Hence, when it comes to autoflower marijuana seedling pots, you are better off planting your seeds directly into the final growing pot, which can be anywhere from 5 liters to 15-20 liters depending on the expected size of the strain that you have chosen, as well as the available space and light in your growing area.

What type of soil or medium is best for seedlings

Cannabis prefers to grow in slightly acidic soil, with a pH of about 6.3 to 6.5. The soil must be well drained and aerated, meaning it should have good nutrtition retention and the ability to pass air through it. This ensures healthy roots and sustained delivery of nutrition throughout the life cycle of the plant.

Most growers will choose to mix perlite (20%-50%) into their soil to help with both aeration and nutrient retention. It also helps with better water drainage, which helps you avoid conditions like root rot.

Seeds should only be germinated in neutral soil or grow medium like cocopeat that does not have a lot of nutrition in it. This is because seeds are extremely sensitive to nutrition and too much additional nutrition in the plant can cause the seedlings to fail and die.

Mixing perlite into compost to make potting mix for good aeration and nutrient retention
Potting mix from perlite and compost is a good medium to help with both aeration and nutrient retention

Creating the perfect climate for your seedlings?

Your seedlings need the right environment to thrive and reach their full growth potential. So let’s look at how to give them the best growth conditions by setting the grow room temperature and humidity correctly.


The ideal marijuana seedling temperature is about 20-25°C when the lights are on and about 15-20°C when the lights are off, creating a clear day to night transition. Higher temperatures, such as when the lights are too close to cannabis seedling, can harm the plant and even kill it. Curled up leaves are a sure sign of heat stress in your marijuana seedling.

On the other hand, a wilting cannabis seedling with slow growth is a sign of cold stress where the ambient temperature is just too low for nutrient mobility. This can also kill the plant. To avoid both extremes, just remember that marijuana plants prefer the same temperatures as human beings. So if you feel like it is too hot or too cold in your grow space, it’s probably a good time to check the temperatures and adjust them.

Planting them at the right time of the year for your location will ensure that they do not suffer from heat or cold stress and it will also save them from too much humidity.


The cannabis seedling growth phase requires a relative humidity of about 40% to 60% because the leaves draw water from the air through osmosis instead of the roots drawing it from the soil. Marijuana seedlings have roots that have just started to develop and so they are unable to provide the water supply that the plant need to grow.

Controlling the temperature and humidity of your grow room is critical. Be careful that the humidity does not exceed 60%, otherwise their will water retention on the plant, causing wet spots to develop. This will give rise to fungal growth that can eventually take over your plant and kill it. It will also act as a attractor for pests that love to thrive in wet conditions and feed on your plant.

How much light do marijuana seedlings need?

A marijuana seedling needs just the right amount of light. Too much light will cause symptoms similar to heat stress and the leaves will start to crinkle and show burned spots. Too little light will cause the seedling to stretch out, become too tall and lanky and then topple over as a result. Avoid both situations by using low intensity, blue spectrum lights for the first 10 to 14 days. 

Marijuana seedling light schedule is around 18/6, meaning the lights should remain off for 6 hours to mimic night time. At this time, avoid any light leakage into your grow area. While it is not as important as the flowering stage, it can still cause stress during the seedling phase.

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Watering and feeding your seedlings

A cannabis seedling is a very senstive being and it needs just the right amount of water and nutrients to survive. Here are the basics of watering and feeding your marijuana seedling.

How frequently should I water seedlings?

You should water your seedling only when the soil has completely dried out. This will ensure that you do not accidentally overwater the seedling. The cannabis seedling growth depends on the development of its root structure. Too much water will stymie this growth and might even kill it.

Always water minimally and around the stem of your seedling. Since it is a tiny plant, it does not really need much water. So avoid pouring in too much water. Some growers will use a hand mister to gently moisten the soil around their cannabis seedling. This is a good option to prevent overwatering.

How do I know if I have overwatered my seedlings?

The leaves will start to show damaged tips, which is a sure sign of water damage. If this happens. Stop watering the plant till the soil is completely dry. If the leaves start to droop, it means the plant needs water and then you can proceed carefully by adding just a little bit of water and observing the plant as it comes back to proper balance.

Sometimes overwatering and underwatering will look the same. So look at the soil and dig your finger into the soil to see how dry or wet it is.

What are the signs of underwatering?

Your plant will start to droop and the leaves will look limp and lifeless. This is the surest sign of underwatering. If you leave your plant in this state, it is likely to die. However, at the earliest stages, this is does not cause permanent damage. The leaves droop when they use up all the water inside of them and the internal water pressure that keeps them erect begins to fall. Watering them a little will bring them right back up. However, it is important to do this before the lack of water begins to kill of the leaves and then the plant.

Should I give my seedlings nutrients?

While cannabis nutrient is an important consideration at later stage, at this stage, you should NOT give any nutrients to your marijuana seedling. Seedlings are very sensitive to nutrition and they do not need that much to begin with. They will usually get all the need from the starter grow medium and the water that is given to them (as long as it is regular water and not RO water). Adding seeds to nutrient rich soil or adding nutrients to the soil will cause nutrient burn and might kill the seedling.

Most of the energy of the seedling is coming from the seed and the nutrients held inside the seed. So there’s no need for external nutrients at this point. When the true leaves have progressed from being three fingered to five or seven fingered, then you can begin to add nutrients to the soil in small quantities. This is when the vegetative growth stage begins.

How to fix stretching seedlings?

If your seedling has already stretched, you can try to support them and grow them under lower intensity, blue dominant light source. The best practice is to place them in the correct light to begin with and avoid long dark periods post germination. Long dark periods like 24 hours will make them reach out to the light source and cause abnormal, stretched out stalks, which will ultimately fail and topple over.

marijuana seedling with stretched out stalk
This marijuana seedling with stretched out stalk would need some support

How to avoid seedlings damping off?

Damping off seedling is a problem related to the Fusarium, Botrytis, or Pythium fungi. These fungi are usually found infecting the root system and the symptoms do not manifest until it is too late to save the seedling. As a result, the seedling will suddenly go limp and die within 24 hours.

The only cure for this is proper prevention. Avoid overwatering your plant and sterilise your grow medium by baking it in the overn until the soil is at 85°C. This will kill of any dormant fungi that might harm your cannabis seedling.

Remove any dead or dying seedling from your grow area so that the infection cannot spread.

Let the growth begin!

Now that you know the basics of growing a healthy cannabis seedling, get out there and try it out. Getting an easy to grow strain that can deal with unintentional stress is a good way to begin your growing journey. Choose professional grow mediums and lighting to make your experience a smooth and rewarding one.

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Joe Musgrave

An avid 420 enthusiast, grower, smoker and writer. Joe writes non stop, sharing his extensive knowledge in the field of cannabis with the wider online 420 community through blogs like ours at High Yield Strains.

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