What Are Cannabis Seedlings?

What Are Cannabis Seedlings?

Luke Sholl
Luke Sholl

Seedlings are tiny cannabis plants that just sprouted into the world. After cannabis seeds pop open, the main root, called the taproot, shoots out. When transferred to soil or another growing medium, a green seedling will eventually emerge from the surface. Any cannabis grower can tell you that the moment a seedling rises, it’s a very special and joyous occasion.

All seedlings look virtually the same; it's impossible to differentiate cannabis strains based on their visual appearance at this stage in the game. In order for cannabis seeds to properly split open during germination, they must be subject to humid conditions. Once the taproot grows long enough, seedlings with two small sets of teardrop-shaped leaves supported by a thin stem will appear. During the rise, the seed husk naturally detaches, however, sometimes it needs to be surgically removed. These tiny “sucker leaves” will mirror each other on top of the seedling, functioning as panels that transform light into energy.

Afterward, two additional leaves will develop from the middle, resembling a regular cannabis leaf shape. The seedling stage is quite short; it takes around a week or two before the seedlings grow into short plants. The seedling stage is technically part of the vegetative phase, but it’s often considered somewhat separate due to unique requirements.

Seedlings need extra attention because they’re small and very fragile. Mistakes during this stage can be detrimental to the future growth of your plant. Here are some tips and tricks to provide your seedlings with the ultimate care.

The correct container for a cannabis seedling


After the seeds have split, they’re ready to be sown. The container size for your seedlings should be relatively small. They can even be planted in disposable plastic cups. Then, once they rise to the surface and grow for about a week, they should be moved to larger containers. If seedlings are left for a longer period in small containers, the roots will begin to grow around the sides of the container, making the plants “root bound". This is undesirable because the roots won’t pick up nutrients in the ideal way, and the water might not drain properly.

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Selecting The Correct Container For Your Cannabis Plants

One must consider that seedlings develop a surprisingly long tap root. Giving them space to grow will allow the seedlings to stabilise and become stronger. The container needs to have a solid drainage system. This can be done by puncturing holes in the plastic cups or by simply purchasing a container with holes at the bottom. This will allow the taproot to dig its environment, pun intended. Outdoor-grown seedlings must be protected from pesky pests.

One could cut and detach the bottom half of a plastic bottle, punch some holes in it, and place it over the seedling. This will allow the sunlight to penetrate, some airflow to enter, and a defensive shield to protect the seedling from enemies. Many growers prefer to place photoperiodic seedlings directly in the container where they'll finish flowering to reduce the stress created by transplant shock. This is up to the grower to decide; one can achieve great results with both methods. One thing's for sure, autoflowering varieties shouldn't be transplanted. They should be directly planted in the container where they’ll finish flowering.

Growing medium for cannabis seedlings


The growing medium quality matters a great deal. Clay-based soil should be avoided because it retains too much water for seedlings, which can lead to various issues. When seedlings are planted in a growing medium that barely retains any water, they can dry out. It’s best to choose a soil with a loose texture, is dark and rich, retains water, and doesn’t get muddy when wet.

It’s crucial to use soil that hasn’t been over-treated with fertilisers, which is called “hot” soil. This can lead to nutrient toxicity for the seeds. Although many growing mediums with fertilisers work great for seedlings, the fertiliser content needs to be on the lower end of the spectrum.

Watering your seedling

4 Watering Your Seedlings

Seedlings need to be subjected to a very humid environment to thrive. During the first 1-2 weeks, the soil around the stem and tap root should be constantly wet. However, the soil shouldn’t be oversaturated, otherwise the seedlings will suffer. Think of it like this; when the soil looks absolutely drenched, it's too wet. If the soil is moving away from the sides of the container and feels crusty, it’s too dry.

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How To Water Cannabis Plants

If the container is larger than the seedling requires, one could water slowly, directly by the stem, so the water gently moves down along the taproot. Of course, the water needs to be pH controlled. Between 6.0-6.5pH will do. One should not water directly on the seedlings because the droplets can function as a magnifying glass, creating heat damage from the sun.

Cannabis seedlings and light


When seedlings are grown outdoors, they can be placed directly under the sun - no problems there. On the other hand, indoor growers are presented with some challenges. When seedlings are placed under strong lamps, they can be overwhelmed and stagnate in growth. If the lights are too far away, they will stretch in an attempt to get closer to the light source, which produces long and weak stems. This can also happen when the soil surface is too deep down in the container.

Some indoor growers prefer to place seedlings under CFL lights because they don’t produce much heat. Normal LED or HPS lights will do, as long as the seedlings receive a lower dose of light than they require during the vegetative phase. Seedlings are like babies; they can’t handle adult amounts of virtually anything.

The heat emanating from the lights can be way too hot. The perfect temperature for seedlings is around 20-25°C. 18 hours of light and 6 hours of darkness will do just fine. When seedlings receive too little light, they’ll lose colour and become weak. If they receive too much light, they can be overheated and at risk of something called “light saturation”, meaning they'll receive too much energy to have the need to grow further.

Luke Sholl
Luke Sholl
Luke Sholl has been writing about cannabis, the wellness potential of cannabinoids, and the positive influence of nature for over a decade. Working with several cannabinoid-centric publications, he publishes a variety of digital content, supported by strong technical knowledge and thorough research.