Cannabis seedling stage how-to guide

For some growers, the cannabis seedling stage can be a slightly nervous time especially for the less experienced. During the cannabis seedling stage the plant is small, fragile and at its most vulnerable. Mistakes with the environment, nutrients or the wrong light height can spell an early end for a cannabis seedling. But if you follow a few basic rules you will find that cannabis seedling care is easy to master.

Basic tips on cannabis seedlings care

Cannabis seedling is the name given to small cannabis plants for the first couple of weeks after germination. The term ‘cannabis seedlings’ is an informal term used for the first stages of growth. Transitioning from a cannabis seedling to a young plant is regarded as a process, rather than an event that happens when a cannabis seedling is a specific age or particular size.

To grow a healthy cannabis seedling you will need to combine several important factors. You need to begin with stable cannabis genetics from a proven supplier. Buy the best cannabis seeds you can from a supplier you can trust. You will also need a solid cannabis seed germination method with a high success rate. Then you will need to select some good grow containers and grow medium/grow method.

Once you have bought your cannabis seeds the first challenge is to germinate them with the highest germination rates. This is often an area where new growers can benefit tremendously from good advice. It doesn’t matter whether you are germinating autoflower seeds or photoperiod feminised cannabis seeds, the same germination methods work well for both. But of all the various cannabis seed germination methods, which is the best one?

What kind of germination method is best for cannabis seedlings?

All the best cannabis seed suppliers should be able to supply high quality cannabis genetics with 90%+ germination rates. But if you buy poor quality cannabis seeds you will get low germination rates regardless of your preferred germination method.

With many decades of experience with cannabis seeds, the Dutch Passion experts recommend germinating your cannabis seeds between two lightly moistened cotton pads for a couple of days. Note that it’s vital just to spray each cotton pad lightly 2-3 times with water mist. Moist germination conditions have a greater germination latitude than soaked germination conditions.

The Dutch Passion germination method using moist cotton pads is the easiest way to get maximum cannabis seed germination rates.

Related:
Moist cotton pad cannabis seed germination method

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Cannabis Seed Germination: The Cotton Pad Method from Dutch Passion on Vimeo.

How much water do cannabis seedlings need?

Seedlings need very little water. As small plants they have low transpiration rates and little need for water. Furthermore, the small and immature root system in the cannabis seedling stage is incapable of utilising high amounts of water/moisture.

Overwatering cannabis seedlings

An overwatered cannabis seedling will result in the roots sitting in a damp grow medium. When using soil, cannabis roots also need a certain level of root aeration/root oxygenation to grow well.

Cannabis roots will rot if the roots are left for too long in wet, un-oxygenated conditions. Overwatering cannabis seedlings can permanently stunt (restrict) future growth.

Over watering cannabis seedlings is one of the most common errors made by less experienced growers. It generally results in slower plant growth with smaller yields and reduced harvest quality.

Underwatering cannabis seedlings

If you underwater your cannabis seedlings they will become progressively weaker as the roots struggle to seek out sufficient water to survive. The leaves will wilt until the plant is watered again. Under watering compromises all areas of the cannabis seedlings health. Growth slows down and eventually the cannabis seedling will die.

What kind of containers are best for cannabis seedlings?

The use of breathable fabric plant containers and air pots has increased dramatically by the cannabis community over recent years. These allow cannabis seeding growth to proceed at a rapid rate. These containers are also highly recommended for growing adult plants as well as seedlings of cannabis. These containers allow particularly high levels of root oxygenation. In turn, this allows a healthy cannabis root zone and therefore healthy general growth.

When all conditions are optimised, a germinated cannabis seed will grow rapidly. If you have ever seen a cannabis seedling time lapse video you will see how quickly the seedling produces new sets of leaves and grows upwards.

Related:
Everything you need to know about cannabis roots

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Auto Lemon Kix® – Cannabis time lapse from Dutch Passion on Vimeo.

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What kind of nutrients are best for cannabis seedlings?

Cannabis seedling nutrients is an area where many growers have accidentally made mistakes. If you are growing in soil you won’t need to provide any nutrients to your plants for the first couple of weeks.

The soil will provide sufficient nutrition. However some rookie growers assume that starting to offer nutrients to cannabis seedlings will allow faster growth. Unfortunately the opposite can be true. The delicate cannabis root system is simply unable to cope with concentrated nutrients and the plant biochemistry simply doesn’t need them.

The result of excessive nutrients will be browned ‘burnt’ leaf tips and stunted growth. In the worst cases, excessive nutrients will kill the cannabis seedling.

Experienced growers using hydroponics methods may use very dilute specialist seedling nutrients. But even here, the nutrients are used very sparingly and with great caution.

Does the type of soil matter for cannabis seedlings?

Yes, a cannabis seedling soil mix is important for a healthy start. Often growers buy a ‘light mix’ of soil specially designed for smaller plants with lower nutritional needs compared to mature plants.

Some growers add coco fibre to the soil to increase aeration. Many soil suppliers offer lighter soil blends which are recommended for cannabis seedlings. When you transplant the cannabis seedling you can choose a different soil type, perhaps one with added minerals and  nutrition for onward growth.

What is the ideal temperature / humidity for seedlings?

Seedlings don’t grow well in temperature extremes. Try to find a steady cannabis seedling temperature of around 23-25ºC. If the temperatures get too hot the cannabis seedlings may struggle to absorb sufficient water via their roots and may wilt. If the temperature is too cold, growth is reduced and eventually stops.

When it comes to cannabis seedling humidity, cannabis seedlings can tolerate high levels around 60% or above. Moisture can be absorbed through the leaves, this is useful if you are growing cuttings or seedlings with under-developed root systems. However, high humidity levels like these can’t be easily tolerated by mature plants in full bloom where the humidity can cause mold/bud rot.

How much light should cannabis seedlings receive?

Cannabis seedling lighting doesn’t need to be powerful. PPFD light levels of around 100-300 µmol/m²/s is quite common for cannabis seedlings. This can be achieved with a simple T5 fluorescent fixture. 

The cannabis seedling light schedule typically uses 18 hours of daily light whether you are growing autoflower seeds or photoperiod feminised seeds. Some growers use 20 hours of daily light or even 24 hours.

It’s not necessary to use powerful lights until later on in bloom. Many growers will use compact fluorescent light fixtures (‘cfls’). As for how many cfls for a cannabis seedling, it depends on the wattage. Check with the CFL manufacturers guidelines on hanging heights and aim for PPFD levels of 100-300 in your grow room.

How long does the cannabis seedling stage last?

How long is the cannabis seedling stage ? There are no firm rules and opinions vary from grower to growers. But in general the first couple of weeks after germination are often regarded to be the cannabis seedling stage.

When to transplant cannabis seedlings to a bigger pot?

When growing photoperiod feminised seeds many growers will progressively transplant their cannabis seedlings into increasingly larger containers. One general rule is to put the seedling in a bigger container once the leaves have reached the same diameter as the container. So when the leaves are overhanging the edges of your plant pot, you may want to consider transplanting your cannabis seedling.

Unlike autoflowers, photoperiod plants don’t start blooming until daylight hours are reduced to 12 per day. This means your photoperiod plants have time to allow a few days to adapt each time your plants are transplanted in their new containers.

When growing autoflower seeds however, your cannabis plant has a fixed life cycle and you may not want it to spend too much of that time adapting to new conditions following transplanting. That’s why many autoflower growers place the germinated cannabis seedling directly into its final growing container.

Can you tell if a cannabis plant is male or female from a seedling?

Cannabis seedlings are too young to have shown their sex. That means it’s not possible to identify female cannabis plant seedlings until they are several weeks older and mature enough to have shown some male or female pre-flowers.

Cannabis seedling stage most common problems

Cannabis seedling problems are always a worrying time for the grower. Without doubt, prevention is better than cure. That means starting with good quality cannabis seeds, a reliable seed germination method and a grow system/method which you feel confident with. If you do encounter issues, the following information may help.

Related:
Top 10 cannabis germination and seedling mistakes

Identifying healthy vs unhealthy cannabis seedlings

An unhealthy cannabis seedling may have yellow or discoloured leaves. You may also find that your cannabis seedling is not growing. To the experienced eye, the unhealthy cannabis seedling simply doesn’t look the same as the normal healthy looking seedling should. The problems could come from a variety of environmental sources and may be related to lighting, nutrition, temperatures, pH, watering or pests.

Related:
Cannabis pests and diseases

Cannabis seedling not growing (or stopped growing)

If your cannabis seedling has stopped growing it’s a sign of a fundamental problem with the conditions. Check the basics and ensure that the cannabis seedling doesn’t have waterlogged roots.

Ensure the container has drainage holes to allow excess water to drain away. Low temperatures can slow down growth. Cannabis seedling light burn is another possibility. If you have your cannabis seedling under a high power light it could be too intense for the delicate leaf tissues.

Cannabis seedling stretching a lot

Sometimes a cannabis seedling will stretch upwards in the search for light, known as cannabis seedling stretch. This can result in an elongated and weak stem which may struggle to support the cannabis seedling.

You can try increasing the light levels by reducing the light hanging height (check with manufacturers instructions). Slightly higher intensity light can restrict the cannabis seedling stretch. Some growers may try to prop up the seedling to support it until the stem has sufficient strength to support itself.

Cannabis seedling leaves curling up

If you see a cannabis seedling with leaves curling up it could be due to heat stress. This can cause the edges of the leaves to curl. This can be more common for growers with HPS grow lights which can produce high heat levels. At the cannabis seedling stage aim for stable, consistent temperatures around 23-25ºC. Remember the cannabis seedlings won’t require intense light levels or powerful lights until they are much older.

Cannabis seedling leaves curling down

When your cannabis seedling shows leaves curling down it is sometimes referred to as claw leaves (they look like a claw, with the fingers facing down). This can be caused by too many nutrients/minerals, Nitrogen toxicity is one typical cause.

Other issues can cause cannabis seedling leaves to curl downwards too. Overwatering can cause leaves to droop. Under watering will cause the leaves to wilt. An unhealthy root structure won’t be able to absorb the necessary moisture and this could also cause leaves to curl down. If you are a hydroponic grower with cannabis root rot you can definitely expect to see issues until you remove the pathogens. If you are a soil grower with a root bound plant you may see leaves curling down and a generally unhealthy appearance.

Pests such as Broad mites and Russet mites can also damage your plants causing leaves to droop or curl down. Fungus gnats can cause the same issues if they completely infest your plant (the larvae live underground, where they can severely damage roots until they can fly). The range of potential issues that could cause leaves to curl down is quite extensive. The best advice is to prevent issues, rather than try to cure a severely damaged plant.

Cannabis seedling leaves turning yellow

A cannabis seedling with yellow leaves is always a worrying sight. Many issues can cause yellowing leaves on cannabis seedlings. It could be overwatering or too much light (‘light burn’).

Pest infestations can also cause yellowing leaves. Root bound plants can also show yellow leaves even if they are being well cared for. If you notice a large tangled mass of white roots at the bottom of your container when transplanting it may be a sign that the plant was root bound.

Nitrogen deficiency can also be a potential cause of a cannabis seedling with leaves turning yellow. Even though seedlings need very little nutrition, they can show deficiencies especially if germinated in very poor soil (or coco fibre). If this is the case, a light feed with Nitrogen rich nutrients may help.

When to drop a sick cannabis seedling

As a matter of last resort when all else has failed, with a sick cannabis seedling knowing when to give up is useful. Sometimes a cannabis seedling is simply damaged so much that it can’t recover.

This happens when a cannabis seedling has spent too long in a poor state of health. Even introducing the seedling to optimised conditions doesn’t really help. At that point it could be time to reach for your cannabis seed collection and select a new seed to germinate.

Optimised conditions and cannabis seedlings

If you use quality cannabis seeds and have a good germination method alongside a stable grow room environment then you should produce plenty of healthy seedlings without too much effort. Where possible, keep working towards optimising your grow room conditions as much as you can and enjoy watching your cannabis seedlings develop into top quality harvest-ready plants!

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Optimising your grow room conditions