Surviving the marijuana seedling stage

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So, you’ve finally bit the bullet and dropped some of your hard-earned cash on a couple of top-shelf cannabis seeds. But before you get ahead yourself, with dreams of pound-plus harvests from each of those beautiful little brown beans, you’re gonna have to make it through the seedling stage.

The marijuana seedling stage is a critical time in the plant’s lifecycle. This is the point where the plants are at their most vulnerable, and if they don’t get the right conditions during this time, they may suffer long-term from stunted growth or worse. Many a novice grower has let their excitement turn into over-confidence, resulting in an empty wallet and a dead crop.

Fortunately, cannabis seedlings are (for the most part) tough little buggers. With the right know-how and a little bit of care, you can 100% get your plants through this critical stage of growth and onto the next. Enough chitter chatter, let’s jump in and discuss some of the key points to keep in mind when your weed crop is in the seedling stage.

When does the seedling stage start?

The seedling stage begins once your cannabis seeds have germinated and the first two true leaves appear. The two leaves are not the classic, jagged-edged, cannabis greenery you are probably expecting to see. These first two leaves are known as cotyledons and are small and oval in shape. They serve two main purposes – to help the baby plant break free of its seedy prison while also being the first photosynthesizing part of the plant.

Once these cotyledons have burst through the seed shell and popped up, the marijuana seedling stage has officially begun. Most cultivators consider their plants to stay in the seedling stage for between 2 to 3 weeks, or until the first five-pointed leaves emerge. This can change from strain to strain though, with some cultivars showing five-pointed leaf growth earlier than others.

Choosing the correct pots and soil for your plants

When deciding on the pot type and size for your cannabis seedlings, there are a few key factors to consider. The same goes for the soil or medium.

What type of soil or medium is best for seedlings

Cannabis seedling growing in mix of soil and coco coir
Cannabis seedling growing in mix of soil and coco coir

If you are new to growing weed, or gardening in general, then you may be uninitiated to the fact that not all growers use soil in their pots. Sure, you would have heard of hydroponic cultivation, but how about coco-coir?

Coco-coir strikes the perfect balance between soil and hydro-cultivation techniques. It’s an inert substance, meaning it contains no nutrients (like hydro), but it also acts just like soil in terms of holding the root structure, with a few key benefits. It offers far better root zone oxygenation and has a superior drainage rate while still holding the perfect amount of moisture for plant growth.

It does come with some downsides though. If you are looking for a plant-and-forget kind of set-up, then coco-coir (or hydro cultivation in general) is not for you. With this type of growing you are going to have to keep a keen eye on the nutrient levels in the feed water, and while this type of control can lead to increased yields, bud density, and cannabinoid potency – it does take a bit more effort on the part of the grower.

So, what is the best soil or substrate for novice growers?

We usually recommend a mix of coco and soil for new growers. A balanced mix of FoxFarm FX14054 Happy Frog Potting Soil and DaKine 420 Coco Coir Lite is absolutely perfect for weed seedlings.

What are the best pots for growing cannabis seeds?

These days, most growers using a soil or coco-based medium opt for fabric smart pots. 

And with the outstanding levels of root zone oxygenation and the increased drainage (when compared to the cheap, traditional plastic pots) it’s pretty easy to see why.

You can still get great results with cheaper plastic pots, or your regular garden terracotta pieces, but fabric smart pots are your best bet.

And how about the pot size for weed seedlings?

You can start small. We usually start our babies off in 1-liter pots and then transplant them into their final pots after a week or so.

What pots should you use for autoflower seeds?

Autos are a different story. 

Since they only have a finite vegetative growth period, you have to be much more careful not to stunt their growth at all. So, for autos, we always recommend planting directly to their final pot. For autos to reach their full potential, you want them in an 11-liter pot (3-gallon), if not slightly larger.

Creating the perfect climate for your seedlings?

Creating the ideal environmental conditions for your cannabis seedlings is key to success. Seedlings like an environment with slightly more humidity than older plants, as the little ones have smaller root systems. This means that they need to grab more of their hydration through the leaf structure, so a slightly more humid environment is perfect.


If you can keep the temperature between 72 and 80 degrees Fahrenheit (that’s 22 to 26 degrees Celcius), then you are on the right path. Some strains like a slightly warmer climate, while others like it a little cooler.


For the seedlings, you are gonna want to keep the relative humidity between 65 and 70 percent. As they enter the vegetative growth stage (once you see five-pointed leaves) you can drop that down to between 55 to 60 percent.

These days, most seed banks offer a fair bit of advice when it comes to temp and humidity levels for each specific strain. If you have any pressing questions about any of the seeds you buy here, feel free to reach out directly to us, or to the seed company itself.

How much light do marijuana seedlings need?

Cannabis is a light-loving plant.  Marijuana seedling light schedules can be a little confusing for beginner growers, but its all pretty straightforward.

  • For seedlings, a lighting schedule of 16/8 is what a lot of cultivators go for. A 12W CFL  will provide the perfect amount of light for 1 or 2 seedlings, and should be hung at a distance of 5 cm above the seedlings. Once they start to show the classic cannabis-shaped leaves you can switch to the following schedules
  • When growing photoperiodic marijuana, it is usually recommended that you keep them under an 18/6 light-to-dark split until it’s time for them to go into the flowering growth stage. At that point, you can switch the light to 12/12.
  • Autoflowering cannabis can be kept under 24 hours of light for the entire lifecycle if you wish. And while there are plenty of grow diaries out there showing great results with autos that have been grown under continuous light, we usually run ours under 20/4 for the entire run.

Watering and feeding your seedlings

Watering and feeding your seedlings is important, but understanding exactly what they specifically need during each stage of growth is absolutely imperative to the success of your crop. Seedlings need much less water and nutrients than a plant that is midway through the flowering growth stage, and the ratio of nutrients is totally different also.

watering cannabis seedlings
Watering cannabis seedlings using a plastic bottle

How frequently should I water seedlings?

For weed seedlings, daily watering is not required. In fact, we recommend you let the soil dry out a bit between waterings. 

As soon as the top inch of the soil starts to feel dry, you can give them a little top-up. If you are handling the pots regularly, you will get to know the difference in weight between a wet and dry pot. It’s a good practice to let the soil dry out between waterings, as this promotes root growth. The root system will expand as it goes searching for moist soil, which will equal a larger overall plant structure and bigger yields.

Most cultivators water their seedlings every 2 to 4 days.

How much water should I give to each seedling?

That really depends on your pot size. The general rule when watering cannabis seedlings (and all cannabis plants) is to water until you see 25 percent of the water exiting the pot through the drainage holes. This water is referred to as ‘run-off’.

How do I know if I have overwatered my seedlings?

There are a few telltale signs that a weed plant is overwatered, and this can have a pretty detrimental effect on cannabis seedling growth if not fixed. The most obvious signs that a seedling has been over-watered are

  • Wilting or drooping leaves, with downward curling edges.
  • Leaves that wilt or droop almost as soon as the plant is watered.
  • The leaves seem a little bloated.
  • Brown spots on the leaf edges.
  • The plant may appear yellowish in color.

If you think you may have overwatered your cannabis seedlings, it’s best to give the medium time to dry out. You may be using pots with insufficient drainage holes, and once the plants have been potted it’s pretty difficult to fix this.

Most cheap plastic pots do not have enough drainage holes, so if you are using these then remember to drill some extras in before planting. You can also add a layer of clean pebbles to the bottom of the pot, as this will increase the drainage capabilities.

What are the signs of underwatering?

Weed seedlings that haven’t been given enough water will show similar signs as seedlings that have been overwatered, which can lead to some confusion. There are some obvious differences though. Underwatered seedlings will have

  • Drooping and lifeless-looking leaves.
  • Paper thin leaves.
  • Leaves that react positively to being watered, and perk right up.

Underwatering issues are easy to skip as long as you water your seedlings every 2 to 4 days, and until you see 25 percent run-off.

Should I give my seedlings nutrients?

Cannabis seedlings will need a certain level of nutrients to grow, but this level is much lower than what a plant in the vegetative or flowering stage will require. The seeds actually come with enough of the essential nutrients for the plant to survive for the first 4 days or so, meaning you can start your seeds in an inert substrate like a Rockwool cube without having to worry.

If, after the first few days, you transplant into a pot with a decent soil mix then there should be more than enough nutrients for the first month or so without you having to worry about adding anything extra at all.

If you are growing in a pure coco-coir blend, or with a hydroponic setup, then you are going to need to supply low levels of nutrients to the seedling in the feed water.

How to fix stretching seedlings

Cannabis seedling stretching in soil during the early seedling stage of growth
Cannabis seedling stretching – A common issue during the seedling stage of growth

There are a few ways to ensure your seedlings do not stretch, and fix the problem if you notice them stretching.

  • Keep the 12W CFL  at a distance of 5 cm, and move it upwards as the plant grows while keeping the same distance.
  • Keep the heat down. Sweltering grow rooms will boost seedling stretching.
  • It might seem counter-intuitive, but seedlings that receive too much light per day can also stretch. Keep it to 16 hours and you should see great results.
  • Make sure the light isn’t too red. Blue spectrum light promotes smaller internodal length, and less stretching

How to avoid seedlings damping off

While damping off is a pretty common disease that cannabis cultivators deal with, there are a couple of easy ways to make sure you cut the chances of it plaguing your crop to almost zero.

  • Damping off is a fungal issue. It can be caused by soil or coco that hasn’t been properly sterilized, so make sure you always purchase top-shelf products like FoxFarm FX14054 Happy Frog Potting Soil and DaKine 420 Coco Coir Lite.
  • Soil or coco with bad drainage can also increase the chances of damping off seedlings. Make sure your pots have enough drainage holes and add perlite to your soil or coco mix to help with drainage.
  • Excessively humid grow areas have a higher chance of causing seedling damping off. Keep your humidity levels below 70 percent and you should be fine.


The marijuana seedling stage is one of the most important stages in any cannabis cultivators journey. It’s essential to get things right if you want your plants to grow into healthy and strong adults, so it pays to spend a bit of extra time getting everything perfect.

With the right amount of light, water, and nutrients, and enough attention to detail, you are going to give those seedlings the best chance at blooming into big, strong, healthy plants. So, off you go – get planting!

Sam North

Sam’s background in canna-agriculture has given him a wealth of knowledge and experience that he now uses to help others achieve their cultivation goals. In addition to his work in content writing and SEO, Sam also offers consulting services to cannabis farmers looking to optimize their production. He can help growers identify areas for improvement in their cultivation process and provide guidance on how to maximize their yields and profits.

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