Cannabis seedlings – How to avoid stunted growth

Table of contents

After seed germination, the Cannabis plant enters the seedling stage. In this article, you’ll find information about how to take care of your seedling, some problems that may arise and how to take care of them.

Cannabis seedlings like relatively moist conditions. Temperatures should remain warm and lights should be placed near them and moved up as the plants grow. Finally, a Cannabis seedling needs little amounts of nutrients and their needs will grow as the plant gets bigger and stronger.

Seedling stage (2 to 3 weeks)

When the Marijuana seed opens, the first pair of small round leaves that appear are called “cotyledons”. After that, the little Cannabis plant starts producing serrated leaves, not the characteristic digitate leaves, only single serrated leaflets. As the plant grows, new leaves with more leaflets start to develop until the plant produces digitate leaves with serrated borders we can all identify as Cannabis fan leaves. When these leaves appear, the plant enters into the vegetative stage. This process may take up to three weeks.

Factors that lead to healthy growth of Cannabis seedlings

  • Warm temperature: Seedlings are very sensitive to temperature, they thrive with temperatures around 72 – 79 F (22 – 26º C).
  • Relatively low light intensity: Young plants are not yet able to process high-intensity light. Led lights or low wattage lights are better for this stage. A cold (blue) spectrum light is better for this stage, as they promote vegetative growth.
  • Adequate light distance: Keep in mind the distance between the plant and the grow lights, which depends on their intensity and temperature. Start with a distance of about 4 inches (10 cm) if you are growing with low-intensity lights and do the “hand test”, placing your hands on the top of your plants for 30 seconds. If it feels like too much heat for your hand, it’s probably too much for the plant too, so move up your lamp until it feels warm but not hot. When growing outdoors, just try to place your plants where the sunlight reaches them and keep an eye on them so the soil never gets to dry up.
  • Light/Photoperiod: Start with 18 hours of light and 6 hours of darkness.
  • Nutrition: Seedlings need a low dosage of nutrients or they may experience nutrient burn. If you are growing on soil, choose light mixes and avoid extra fertilization in the first week or two. After that, you can start your fertilizing plan.
  • Pot size: Once germinated, place your seed/seedling in a small pot or cup with drainage for better results. Then move your seedling to a bigger pot once it has grown a few cms or if you see the roots coming out through the drainage holes. 
  • Watering: Water your seedlings with a sprayer to avoid overwatering. Use clean water only.
  • Relative humidity: A very dry environment may cause your seedling to dry up easily. Keep it around 65 – 80%.
  • pH levels: Keep pH levels between 6.5 and 7 for your seedling to be able to absorb all the nutrients present in the substrate.

Always keep an eye on these factors, if they are not taken care of, your plant may experience stunted growth and finally die. Let’s see the typical problems a seedling may have.

Factors that lead to stunted growth of Cannabis seedlings

Your marijuana seedling is not growing? There are many factors that may lead to stunted growth in the seedling stage, let’s take a look at some of them.

Problems with watering and pot size

Underwatering and overwatering may cause stunted growth. Small seedlings growing in big pots may experience overwatering problems, as roots need oxygen to develop and their roots systems are yet incapable of drinking that much water. In this case, the seedling seems droopy and weak, because they are slowly drowning. If this is the case, just add less water and only around the seedling, let the plant absorb some of it before watering again.

On the contrary, if the pot is too small for the seedling, growth would be stunted as well. The roots need space to develop and your risks of having problems with watering are high. In this case, just transplant it to a bigger pot to avoid “root bound”. Poor drainage also leads to these problems.

Problems with nutrients

Nutrients toxicity usually happens when the growing medium has too many nutrients for the stage and the plants are not able to absorb them. You’ll notice burnt tips and a dark green color in the leaves if this is the case.

Nutrient deficiency may happen either because of the growing medium not having any of them or because it has too much of them, so pH levels are off and those nutrients are not available for the plant to uptake, despite being present in the mix. The most common at this stage is Nitrogen deficiency, which shows with older leaves turning yellow and then brown and crispy.

Sometimes, this happens also when the plant is in a very small pot and has already used all the nutrients in the soil. If this is the case, the best idea is to transplant it into a bigger pot containing a soil mix and apply nutrients for the vegetative stage. Remember to monitor watering schedules for better results.

Problems with temperature

If temperatures are too high or too low, seedlings are bound to experience stunted growth. This shows with leaves tips turning up and curling. If this is the case, lower the environment temperature and monitor for changes. As stated before, keep the environment temperatures between 72 – 79 F (22 – 26º C).

Problems with light

Too much light or not enough light also leads to stunted growth.

If your seedlings are not receiving enough light, they’ll grow very tall and weak, with few leaves. You’ll see the stem growing tall and white.  If this is the case, your growing light needs to be closer to the plant. Always do the “hand test”, placing your hands on the top of your plants for 30 seconds. So, if it feels like too much heat for your hand, it’s probably too much for the plant too, so move up your lamp until it feels warm but not hot.

When they are receiving too much light, leaves are curled and seem burnt. If this is the case, move your lights up and also do the “hand test”.

cannabis seedling with stretched stem
Cannabis seedling with stretched stem
PH: Chanvre QuebecFe

Take care of your Cannabis seedlings!

At the seedling stage, Cannabis plants are very sensitive and vulnerable, their root system is not yet developed and they need special care, little watering, and humidity. A healthy seedling has a short stem and green leaves.

Remember to take notes about this stage and monitor your environmental factors. You can do this with our free app Grow with Jane! Follow this link to download it today. Get the Grow with Jane app.

Hopefully, your seedling will rapidly grow and enter the next stage a healthy plant. As said before, when the digitate leaves with serrated borders we can all identify as Cannabis fan leaves appear, the plant enters into the vegetative stage.

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28 thoughts on “Cannabis seedlings – How to avoid stunted growth”

  1. Thank you so much for your response. I am growing white widow autoflowering feminized seeds. This one is growing well. The other is bubba kush. I planted them at the same time. However the kush although has a stem, the seed is still attached to the stem and I don’t see any leaves. What should I do? I don’t understand why one looks fine but the other won’t let go of the root. Can you advise me? Ty

    Reply
    • Hello, Elizabeth! Not every plant grows at the same rate, that’s completely normal. The seed shell normally falls off when the two first round leaves (cotyledons) are formed. Sometimes, this shell is very hard and gets attached to the already formed cotyledons. You can gently spray it with clean water to soften the shell, leave it for a few more hours and watch for changes. Another option is to keep your seedling in a very humid environment, that helps too.
      If it doesn’t fall and you decide to take it off, you can try spraying it a little more and gently take the shell off using sterilized tweezers. Be very careful not to force it and damage the seedling!
      Thanks for contacting us! I hope those seedlings start to grow strong soon. Those are great strains to grow!

      Reply
    • I’m growing outside and my cannabis seed sprouted but a slug ate the cotyledons. I caught it early enough that the stem is still there. Can my little seedling bounce back??

      Reply
      • Hi! I’m sorry to hear this! Damaged seedlings may recover if they grow a pair of leaves soon enough, but it’s difficult for them.
        Next time, I’d recommend starting the germination process indoors and take your plant outside once it has grown a few leaves to avoid pests from eating your seedling.

        Reply
  2. Hello I’m growing my first plant I’ve never done it before . I’m excited but there’s one issue It has its 2 cotyledon leafs & it’s true leafs one of the cotyledon leafs has a brown/tan tip how do I cure that ?

    Reply
    • Hello! I hope it’s not too late for this! Tan tips in seedlings may have different causes, most of them related to growing medium, watering or light.
      If you need further help, please upload your photos to the Grow with Jane app. Then send us an in-app message and we’ll be happy to take a look!
      Here’s the link for downloading for free the Grow with Jane app for Ios and Android https://growithjane.com/
      Thanks for reading and commenting!
      Happy growing!

      Reply
  3. Hello, I have been growing white widow and blue Dream for a month and a day, and i am experiencing no growth. It’s still a seedling, and doesn’t have the true set of 5 leaves yet. I’m not sure what I’m doing wrong! I transplanted them into larger cups because their roots had filled the bottom of the solo cup up, but they are STILL seedlings

    Reply
    • Hello! I hope it’s not too late for this! Stunted growth in seedlings may have different causes, sometimes related to lighting, growing medium or watering.
      If you need further help, please upload your photos to the Grow with Jane app. Then send us an in-app message and we’ll be happy to take a look!
      Here’s the link for downloading for free the Grow with Jane app for Ios and Android https://growithjane.com/

      Happy growing!

      Reply
  4. Hi, I am 10 days into an auto Northern lights, I’m concerned because there is just a single thick root still, I wanted to move it to the DWC I have but I cannot still. The color seems ok and the light used also ok, because it has not grown high in this period.

    I wanted to let it grow the roots in a glass with water, keeping the roots submerged, but I am not sure it will make good on it.
    I decided to make a non tight ball of cotton around the roots and place it in a flat pot with humidity.

    I am almost going to get a new one and try again. Should I?

    Reply
    • Hi Guille, seedlings need to be placed in their growing medium as soon as the seed sprouts, even when growing hydroponics.
      If you go for DWC, make sure the water has proper aeration because the roots need water and oxygen to grow. Use air pumps and air stones for this purpose. Use only hydroponic mineral nutrients, check pH and water temperature.
      I’d recommend preparing everything beforehand so as soon as your seed sprouts you can start growing your plant properly.
      Thanks for reading and commenting!

      Reply
  5. Hello! I’ve noticed some of my veg plants have different lengths on the stems, some are very short between “levels” and look busy and others look legging. They are all in the same area with same amount of light +13hrs. 2gal containers they are about 30days old since I started them as seedlings. Also a few seem lighter green and others more foresty green….
    I’m a begginer so I’m having alot of fun with seeds, I mistakenly left 4 newly seeldings thag I transplanted into pots from the ziplock bag and papertowel…super healthy +3imch stems with yellowishgreen cotydelons in the sun at 90F and a couple shriveled up. Medium was still moist can I save them???

    Reply
    • Hello Liliee! Every plant grows at its own pace, according to the light, nutrients available, airflow and genetics. Some strains produce taller plants and some others rather bushy plants. Just be careful, sometimes the tallest plant, that one that has elongated before the others, turns out to be a male. Just check the nodes (where the branches meet the stems) for signs of preflowers. Here’s an article I wrote about how to determine your plant’s gender. https://growithjane.com/determining-sex-cannabis-plants-male-female-hermie/
      Regarding those seedlings that were scorched by the sun, take them inside, spray them with clean water and leave them in a moist environment and low light intensity until they recover.
      If you are planning on starting seedlings indoors and then taking them outdoors, better do it slowly. Just a few hours a day until they get used to their new environment. Never let seedlings unattended in the sun on a very hot day or they might die of dehydration.
      I hope this helps. Thanks for reading and commenting!!
      Happy growing! =)

      Reply
  6. My 2 week old seedling are stunted. I made the mistake of trying to start them in their final 5 gal fabric pot and I also made the mistake of not buffering my coco. Is it possible to try scooping them out and re-potting them at this stage, or should I just start over :-/

    Reply
    • Hi Kym, growing in coco has many advantages but it takes researching and trying different methods until you find the perfect one for you. It requires reading, taking notes, measuring pH, EC, and other things.
      Growing in unbuffered coco leads to stunted growth, mainly caused by Calcium and Magnesium deficiencies. Many plants live 2-3 weeks and then start dying because Ca and Mag are not available to the plant. For now, you may take out these seedlings and try to place them in small containers while you prepare your substrate. Although, it would be a better idea to start over with new seeds if possible. Take out this seedling and prepare your coco for your next grow.
      Here are some tips:
      – Before you use coco, rinse it, buffer it and mix it with perlite to avoid Calcium and Magnesium deficiencies.
      – Buffer coco by soaking it in Ca and Mg solution.
      – Start your next seedlings in small containers, like solo cups. Fill them with coco/perlite.
      – 75% coco – 25% perlite would be a good mix to start. Try to find the perfect one for you
      – Start with low EC and increase it gradually.
      – Keep Ph levels around 6.0 – 6.4
      – Do not let coco substrate dry in the seedling stage. Water/spray your seedlings with a small amount of water, once or twice per day (leaves and soil) – Keep high Relative Humidity (60-80%).

      I hope this helps for starters.
      Thanks for reading and commenting!

      Reply
  7. Hello, newbie here as well.
    I’ve been trying to grow a couple purple kush plants from seeds. I soaked the seeds until they dropped to the bottom of the glass then placed them in presoaked rockwool pods in 5.5 ph water. Two of the seedlings started coming up in about 3 days but they’re taking so slow to grow. It’s been 10 days and still haven’t seen much of any growth. The temperature and humidity are good (22-26 celcius, 90-99 % humidity). The one seedling has just it’s initial leaves but one is starting to brown. I want to put these into a DWG system eventually.

    Reply
    • Hello Brian! Sorry for the delayed response, how are those seedlings going? Temperatures are fine but relative humidity is a little high at 90%-99% levels, this may lead to some fungal infections and dumping off (this may kill seedlings). Try lowering RH to at least 80% until you see the first set of true leaves growing. Also, at this stage seedlings need light to grow.
      If they are not growing it may be due to poor lighting and/or excessive watering. Try giving your seedling 18 hours of low-intensity light positioned not too far away from the plant and watering with a sprayer to avoid stunted growth.
      I hope this helps! Thanks for reading and commenting!

      Reply
    • Hello! If there are no Cannabis specific products available in your area, you can try tomato fertilizers. Just as Cannabis products, they come for the vegetative and flowering stage. They are said to work very well on Cannabis crops. Always check that your fertilizers are not harmful for human consumption, as fruit fertilizers are, for example. If growing organic, worm castings and animal guano (bat, goat, chicken) work great for Cannabis, and complementing them with molasses works even better.
      I’m writing articles about nutrients for Cannabis plants, specially crafted for beginners, so stay tuned!
      I hope your plant grows strong and beautiful! Thanks for reading and commenting!
      Happy growing!

      Reply
  8. Like so many here, I am growing for the first time. I decided to try my first seed (I’m doing them one at a time in the event I screw up) in a peat pod. Germination went well and I put the seed with tap root in the pod 5 days ago. Was happy to see her break the surface a day later and then grow her first set of true leaves on day 2. Then everything kinda stopped. I wasn’t hugely concerned as I have read that in the early stages, lack of action above the soil can mean all kinds of great things (like root growth) are going on beneath. However, I’ve seen very little growth since then and, now in the later part of day 5, the edges of the leaves are turning yellow. I did a bit of research and I have learned that if you are using coco coir you should start nutrients fairly early. Do you know if this is the same with peat? I can’t seem to find anything on this. I am also concerned about PH. To prepare for the next couple of weeks, I went out and bought some nutrients and a PH tester. I tested my water and it seems to have a PH around 7. The manufacturer of the peat pod indicated the pod should have a PH of around 5.5. I did a test where I saturated an empty pod, let it soak for 10 minutes or so and tested the run off. I was shocked to find that the PH was probably about 4.5, maybe 5 if I’m lucky. I should note that I’m using the General Hydroponics drop tester so matching the colour is not as accurate as a PH pen might be. Regardless, it was orange coloured which would make it much more acidic than the optimal 6.5-7.0 range that I believe I’m looking for. The seedling has been under an LED grow light on the 18/6 cycle and the temperature has been maintained at 70F with relative humidity between 65 and 70%. I’d appreciate any thoughts you might have. Now I am going to install your app on my phone. Thanks.

    Reply
    • Hi Jetblack! Thanks for commenting and sorry for the late response. Next time, please send your Grower Support questions as an in-app message in the Grow with Jane app to get answers a lot quicker than in the blog. Also, we can see your Growlog and give you better diagnostics based on your tracked actions and photos!
      Peat is naturally acidic, so it’s normal to get low pH readings. For growing Cannabis, peat can be mixed with Dolomite Lime to increase pH levels. Also, you can add perlite to help to keep air spaces in the substrate. Mixing some worm castings or guano helps plant nutrition and may help to balance pH, but do not rely on it.
      Dolomite lime may be used when preparing the growing medium and you can also re-amend the soil if it becomes too acidic again throughout the plant stages. There are commercial premixed peat-dolomite-perlite substrates, to make things easier. They work great for Cannabis but bear in mind that peat does not contain the necessary nutrients so you’ll need to add them!
      Keep testing for pH levels until you succeed!
      If you need further help with your plant, please send an in-app message and we’ll be happy to help.
      Have a nice day and happy growing!

      Reply
    • Try using Roots Organics Lush soil. It’s a little expensive but it has all the nutrients in the soil you need for growing a healthy plant. So you’ll save money by not having to purchase separate nutrients. You’ll also produce a more organic pure tasting product.

      Reply
    • JetBlack,

      I had the exact same issue while using peat and perlite. I did change to vermiculite but I noticed no differences in my ph run off, still 4.5. I did raise my ph with Bonide Hydrated lime. You can purchase a 10lb bag at your local ACE hardware store for about $12.99. You mix this into you media at a rate of 40g per cubic ft of grow media.
      1 cubic feet = 1 ft2 1 ft2 = 1 cubic feet
      2 cubic feet = 1.5874 ft2 2 ft2 = 2.8284 cubic feet
      3 cubic feet = 2.0801 ft2 3 ft2 = 5.1962 cubic feet

      You should be able to raise your ph to the appropriate level by measuring your run off. Also start your nutrients about 1/2 strength right after about 1-2 weeks from sprouting. It appears you are doing everything else right on the money!
      Hope this helps.

      Reply
  9. Not my first grow but my first time getting a seedling beyond round cotelydon to serrated cotelydon leaves. Sunday one of my cays pulled the seedling from its rockwool dwc home leaving an inch of root in the rockwool cube, I removed the broken root from the wool and gently placed the seedling back into the wool and dwc, and it is showing growth.

    At this point would you say the plant is safe from this trauma? It is showing new growth since the incident. At the time I wasn’t running a light as there was no chlorophyll collectors (leaves). Now I’m running it under a 60watt seedling lamp from Home Depot. Don’t want to overwhelm it with the cob led yet.

    Reply
    • Hi! This sounds very specific. Sometimes seedlings are able to regrow a part of the broken roots, sometimes it doesn’t, but you’d notice in one or two days. If you have more questions about your plants, please download our app from http://www.growithjane.com and contact us via in app message, so you can also share pics and any info you think would be helpful. We’ll be happy to take a look and share some personalized advice!

      Reply
  10. Growing 3 strains 2 are doing great the 3rd is stuck it hasnt had any new growth in weeks and the temp light and feed is spot on…. should i just pull it im about to switch to flower and i just dont think this plant is gonna make it it has to be root bound?

    Reply
    • Hi Shane! When plants become rootbound they stop growing, but it also could be something else. Choosing your best plants for flowering is a good idea if you have limited space and nutrients.
      If you want some personalized advice on your plants, please download our app from http://www.growithjane.com and contact us via in app message, so you can also share pics and any info you think would be helpful. We’ll be happy to take a look and share some growing tips with you!

      Reply

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