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Common Cannabis Seedling Problems and How To Fix Them

Yellowing or deformed leaves, burnt tips, or even slow growth can be a sign that something is wrong, even though your seedling may be able to recover, it may have a toll on the final size and yields of your cannabis plants.

Problems with seedlings are common and can end up affecting them further into their life cycle so it’s vital you detect and fix them as soon as you can.

It’s definitely not hard to detect when something’s wrong, but if you’re a new grower, first you should know how a healthy seedling looks like.

1. Healthy cannabis seedlings

Cannabis seedlings start with two tiny round leaves named “cotyledons”, these leaves are already formed inside the seed and open up once the seed has been successfully germinated, after a couple of days, the first serrated leaves will appear, which indicates that your seedling is starting to grow.

As you seedling start developing, the first pair of true leaves will appear, the true leaves are the typical fingered leaves everybody knows, all of the leaves up to this point should be bright green, if not, it’s a sign that something is wrong, to help you diagnose what you may have, here are the most common cannabis problems.

2. Overwatering

Overwatering is one of the most common problems amongst growers, even though plants need water to grow, they also need oxygen to properly develop, and when overwatering, you may end up drowning your plants because of the lack of oxygen.

You may think What about plants grown in hydroponics? Well, in hydroponic setups, about ⅓ of the roots are kept out of the water, this way they can breathe at the same time that they absorb water so even though the roots are in the water, they still get the oxygen they need.

When your plants don’t get the amount of oxygen they need, the leaves will start getting droopy and if you don’t treat it for long, the leaves will start to get yellow.

If you are seeing any of these symptoms, it’s most likely the problem is being caused by any poor drainage or watering too often.

How to fix it

  • Don’t leave plants sitting in runoff water.
  • Get better containers such as Smart pots or Air pots.
  • Mix perlite into the soil to increase drainage and oxygenation.
  • Make drainage holes on the bottom of the container to allow water to drain.

3. Underwatering

Just like overwatering, underwatering is very common, especially among new growers who want to prevent overwatering and it can be quite confusing because the symptoms are basically the same as when overwatering.

It’s essential you make sure your plants have access to water at all times, the roots should be kept moist always because plants are constantly losing water through the process of transpiration and they need to be able to replenish the water in the leaves.

When there’s not enough water, cannabis plants stop performing their basic processes and dry out, eventually killing them so even though you should be careful when watering, you should definitely keep your plants watered.

How to fix it

  • Make sure the top part of the soil is always moist.
  • Mix soil with coco fiber or vermiculite to improve water retention.

4. Nutrient problems

Just like the symptoms of overwatering or underwatering, plants that suffer from a nutrient excess (overfeeding) will start to get yellow leaves or yellow spots, burnt tips, or show slower growth.

Problems related to nutrients are usually caused by giving nutrients too soon, giving too many nutrients at once or “hot” super soil or pre-amended soils.

Giving too many nutrients at a time can cause problems overnight, so we recommend watering your seedling with plain water and taking a look at the following table so you prevent any problem related to nutrients.

The ideal water for seedlings

Medium pH PPM
Soil 6.0-7.0 100-250
Coco, clay pellets, and hydro 5.5-6.2 300-400

Have in mind that these are estimates and you should check every day for problems and lower or increase these numbers if you see signs of deficiencies.

Giving nutrients too soon will overload the soil, and consequently, your seedling so remember that you shouldn’t feed for the first couple of weeks or at least give a low nutrient dose.

This can also happen with organic super soil, even though it’s organic, you need to wait until your super soil isn’t “hot” anymore, “hot” soil means that the mix is still undergoing through biological activities so you will have to wait around 30-45 days before you can use it, although this is not the case with all super soils so make sure you get more information on the product you’re using.

How to fix it

  • Make sure you adjust the nutrient dose according to the medium you’re growing in.
  • Wait at least 10 days before you start feeding your plants.
  • Read the instructions on the products you’re using.

5. Excessive heat

Excessive heat can also affect your plants, which will end up showing signs of heat stress, you will see the edges of the leaves turning up like tacos and they will start to get dry and crispy, and in more extreme cases, the leaves will start showing a yellowish-green color.

This can be caused by elevated temperatures, low humidity, or even the fans being too strong, but luckily, this can be easily spotted before your plants start showing the symptoms because you will see the soil is dry and sometimes it will start to crack.

How to fix it

  • Make sure the temperature and humidity are at the right levels.
  • Place your hand under the light fixture, if it’s too hot for you, it definitely is for your plants.
  • Ensure your fans are not too strong for the stage your plants are in.

6. Too much (or too little) light

Another common problem among new growers is not providing enough or providing too much light in the seedling stage, if your seedlings are not getting enough light, they will start stretching and the stem will get super long, which is a bad thing because they can easily snap and there’s no way to fix it.

Now, when your seedlings are getting too much light, or the lights are too close to them, the seedling will get dehydrated and the leaves will get burnt, showing symptoms like burned and wrinkled leaves.

How to fix it

  • Adjust the light fixture’s distance from the seedling every day, try to find the sweet spot.
  • Use CFLs instead of potent LEDs or HPS to avoid this kind of problem.

7. In conclusion

Seedlings are super fragile and sensitive so you should take good care of them, avoiding problems at this stage is vital because even though your baby plants may recover, the size and structure may be affected, which will end up affecting your harvest.

If you have tips you can share with fellow growers to help them take care of their baby plants, feel free to leave a comment in the comment section below!

Have you noticed your seedlings are not growing properly? Learn how to identify and fix those problems!

Mastering The Cannabis Seedling Stage In Just 3 Steps

The seedling stage can be a looming challenge for novice growers. With these three simple steps, however, even inexperienced growers can manage their cannabis seedlings with confidence.

Three simple steps to mastering the cannabis seedling stage.

  • 1. Pick the right genetics, containers, and medium for your seedlings
  • 2. Use the right germination techniques
  • 3. Mastering the seedling stage
  • 3.a. The basics: Optimising light, temperature, and humidity for cannabis seedlings
  • 3.b. Growing seedlings outdoors
  • 3.c. Understanding the seedling stage
  • 3.d. How to water your seedlings
  • 3.e. How to prevent damping off
  • 3.f. How to prevent nutrient problems
  • 3.g. How to prevent pests and bugs
  • 3.h. How to prevent stretchy seedlings
  • 3.i. Know when and how to transplant your seedlings
  • 4. Get growing!
  • 1. Pick the right genetics, containers, and medium for your seedlings
  • 2. Use the right germination techniques
  • 3. Mastering the seedling stage
  • 3.a. The basics: Optimising light, temperature, and humidity for cannabis seedlings
  • 3.b. Growing seedlings outdoors
  • 3.c. Understanding the seedling stage
  • 3.d. How to water your seedlings
  • 3.e. How to prevent damping off
  • 3.f. How to prevent nutrient problems
  • 3.g. How to prevent pests and bugs
  • 3.h. How to prevent stretchy seedlings
  • 3.i. Know when and how to transplant your seedlings
  • 4. Get growing!

Cannabis seedlings can be tricky to keep alive, especially for rookie growers. With a solid understanding of seedlings and their requirements, though, the all-important seedling stage can be a lot less threatening. Keep reading for three simple steps to growing healthy seedlings.

STEP 1: PICK THE RIGHT GENETICS, CONTAINERS, AND MEDIUM FOR YOUR SEEDLINGS

When sourcing your seeds, be sure to actively search out the right strain for you; your experience and skill as a grower, budget, grow equipment, preferences in taste and effect, and whether you’re growing indoors or outdoors will determine which strain will yield the best results for you.

As for the medium, we always recommend growing in a light, well-aerated, slightly acidic soil with a pH of 6.3–6.5. We recommend using between 20–50% perlite in your medium to aid with soil aeration and nutrient retention. The more nutrients you plan to give your plants, the more perlite you should add to your soil to help with drainage and prevent nutrient lockout.

Remember to water just around the stem of your seedlings, and only once the soil has completely dried out (see the section on over/underwatering below for more info). Also, keep in mind that seedlings (especially autoflowering varieties) are extremely sensitive to nutrients. Never plant them into hot (nutrient-rich) soil and don’t start feeding them until they’ve grown 3–4 sets of true leaves.

When it comes to picking pots, we recommend the following approaches for autoflowering and feminized seedlings.

THE RIGHT POTS FOR AUTOFLOWERING CANNABIS SEEDS

When growing autoflowers, we recommend planting them directly in their final pots. Because of their short life cycle, it’s best to avoid putting autoflowering strains through any kind of unnecessary stress, including transplanting. While the exact pot size you use will vary depending on the strain you’re growing and the size of your grow space, most auto growers use pots between 5–15l.

THE RIGHT POTS FOR FEMINIZED CANNABIS SEEDS

If you’re growing feminized seeds, transplanting isn’t as much of an issue since these plants have time to recover from the stress. Using Easy Start germination pots, you can support robust health right from the beginning. You’ll want to transplant your seedlings just before they start outgrowing their starter pots. We typically recommend transplanting once they’ve grown sets of true leaves that spread out to cover the full circumference of their current container.

From here, most indoor growers move their plants directly into 12l pots, but you can go above or below that to suit your particular strain and grow setup. Keep in mind that you can (and should) up-pot feminized photoperiod plants a few times to max-out development, meaning you don’t need to transplant your seedlings into a giant pot right away.

A NOTE ON CANNABIS POTS

From cheap nursery containers to sophisticated smart pots, growers are spoilt for choice when it comes to picking the right container for their cannabis plants. And while it’s possible to grow great weed in cheap plastic propagation containers, there are a couple of things you’ll want to keep in mind when choosing pots for your weed plants.

• Drainage holes

Make sure your pots drain well to protect your plants against fungal pathogens and root rot. If your pots don’t already contain holes (or some other kind of mesh to allow runoff), you’ll need to puncture them yourself.

• Aeration

One of the functions of a plant’s substrate is to serve as a site for air exchange between the roots and the environment. Smart pots like the RQS Fabric Pothelp your plant’s roots respire by allowing more oxygen to reach them. This translates into faster, more vigorous growth, healthier plants, and a better harvest.

• Pot size

Keeping tiny seedlings in huge pots increases the risk of overwatering, as your plant’s roots won’t be big enough to extract all the water from their substrate. Any water that stays in the substrate will effectively drown the roots and attract pathogens and pests into your garden/grow room.

STEP 2: USE THE RIGHT GERMINATION TECHNIQUES

Cannabis seeds need four things in order to germinate: moisture, warmth, darkness, and time. To ensure you grow healthy seedlings, germinate your seeds using one of the following techniques.

• Paper towel method

Carefully place your cannabis seeds between a few moist pieces of paper towel, and place it all in a plastic container with a lid. Keep the container in a warm, dark place (temperatures between 20–25°C are ideal). Leave a slight crack in the lid to allow for some fresh air exchange.

• Glass of water method

Simply drop your seeds into a glass of water and let them sit in a cupboard for 24–48 hours at 20–25°C. Once you see the first signs of taproots sprouting from your seeds, they’re ready to plant. If your seeds don’t germinate after 48 hours in water, switch to the paper towel method. Don’t keep the seeds submerged for more than 48 hours or they’ll rot.

Your seeds are ready to plant once they’ve cracked open and released a small, white taproot. Plant your germinated seeds one knuckle (roughly 3–5 millimetres) deep with the taproot facing down. That way, your seedlings won’t have to reorient themselves.

• RQS Starter Kits

Alternatively, use the RQS Autoflowering or Feminized Starter Kits to provide your seeds with the perfect conditions from the get-go. This kit contains starter pots filled with perlite and beneficial bacteria, as well as a propagator and lights to breathe life into your seeds. carla

STEP 3: MASTERING THE SEEDLING STAGE

Now that your seedlings are in their soil, the real challenge begins. Cannabis seedlings are extremely fragile; armed with nothing but frail roots and a small set of cotyledons (that first set of small rectangular leaves), minor stressors can take down your seedlings in just a couple of hours. By taking the time to understand your seedlings and their specific needs, however, you’ll automatically know how to optimise their environment and help them grow into strong vegetative plants.

THE BASICS: OPTIMISING LIGHT, TEMPERATURE, AND HUMIDITY FOR CANNABIS SEEDLINGS

Seedlings have very particular needs when it comes to temperature, humidity, and lighting, and missing the mark in any of these areas can prove fatal for such small plants. For best results, we recommend growing seedlings in a propagator where you can easily create the perfect environment for them to flourish in.

• Temperature

Cannabis seedlings like daytime temperatures of 20–25°C and nighttime temperatures that are roughly 4–5°C cooler. High temperatures will stress your seedlings and stunt their growth, which, at such an early stage, can prove fatal. Dry leaves with curled up edges are a telltale sign of heat stress. With time, your seedlings might also develop other symptoms, including pale foliage and red or purple stems. Heat stress can also cause weak, wilting leaves with downward folding tips.

Cold temperatures, on the other hand, can freeze a seedling’s cells and affect its ability to transport and use nutrients, water, and oxygen. This will result in stunted growth and eventually death if not dealt with properly. Wilting foliage, slow growth, and poor plant turgor are some signs that the temperature in your grow room or propagator is too low.

• Humidity

While their roots are young and still developing, cannabis seedlings absorb water via osmosis in their leaves. To optimise this process, it’s super important to keep relative humidity levels at 40–60%.

Humidity levels below 20% will seriously stunt the growth of your seedlings and may cause them to develop symptoms similar to some nutrient deficiencies (yellow or spotted leaves). Humidity levels above 60%, on the other hand, will cause your plants to develop wet spots that can cause foliage to wilt or rot, as well as attract fungi and/or other pathogens and pests. Once your seedlings enter the vegetative phase, you should keep relative humidity at 50%.

• Lights

Seedlings are sensitive to light and will burn under strong HID or LED bulbs. Like adult plants, seedlings will develop burnt, crinkled leaves when suffering from light stress. Alternatively, seedlings that don’t get enough light will grow tall and lanky and topple over.

For best results, we recommend growing your seedlings under an 18/6 light cycle using CFL bulbs with a blue light spectrum for the first 10–14 days. Once they’ve developed healthy true leaves and at least 2–3 nodes, you can move them under stronger HID or LED lights to start vegging.

GROWING SEEDLINGS OUTDOORS

Outdoor growers obviously don’t have the liberty of being able to change the temperature or humidity with the push of a button. If you’re an outdoor grower, you have three options on how to tackle the seedling stage:

  1. Most growers choose to keep their seedlings indoors under CFL lights for the first two weeks to protect them from elements.
  2. Alternatively, you can keep your seedlings outdoors during the day (as long as temperatures sit consistently between 20–25°C) and only move them indoors at night to protect them from the cold, rain, etc.
  3. Finally, you can keep your seedlings outdoors permanently in a propagator, greenhouse, or polytunnel to provide shelter and allow you to drive up humidity and manipulate the temperature.

UNDERSTANDING THE SEEDLING STAGE

Inside that dark, hard shell, cannabis seeds house all the necessary genetic information to sprout and grow into big, luscious plants. When exposed to humidity and warmth, seeds are able to absorb water from their environment. This process is known as imbibition, and it’s the key to life for all plants.

Once water enters a seed, it activates special enzymes that trigger the growth of the taproot (the small white root that pops out of seeds when germinated properly). This root starts to push deeper underground in search of more water while the seed sends a shoot up and out of the soil in search of light.

Cannabis seeds already contain two cotyledons (or embryonic leaves) that unravel and push the seed casing from the shoot. After the cotyledons emerge, cannabis plants will develop their first set of true leaves. These will grow out of the main stem and have just one finger.

During the early stages of their lives, cannabis seedlings get all their energy from stores inside the seed. As their roots develop, they can absorb water via their leaves. Once your plants have developed their first sets of true leaves (that is, leaves with at least 5–7 fingers), they are no longer considered seedlings and are officially vegging.

Remember, rapid growth and vibrant green foliage are telltale signs of healthy seedlings.

HOW TO WATER YOUR SEEDLINGS

There’s no universal schedule on how to water your cannabis seedlings. Instead, you’ll need to pay close attention to your plants and their medium. We recommend sticking your finger roughly 2.5cm (1 inch) into the soil and watering only when the soil is completely dry. Also, remember to water your plants close to the stem where you know their roots are. Finally, remember that your pots need to have drainage holes in the bottom so excess water can drain out.

• Overwatering

Overwatering seedlings is one of the most common (and most fatal) mistakes rookie growers make. Unfortunately, it’s an easy crime to commit; scared to let their seedlings’ soil dry out, inexperienced growers often end up watering their plants too regularly. This essentially drowns a seedling’s tiny root system, starving the plant of oxygen and causing it to droop.

Overwatering can also occur when a plant’s container is too big or too small. When growing a small seedling in a big pot, the excess soil can hold water for days in areas untouched by the plant’s roots. What you’re left with is a big container filled with wet soil that’s not only robbing your plant of oxygen, but also creating a breeding ground for fungi, bacteria, and pests.

Similarly, under-potting can be just as detrimental to your plants. Plants that are root-bound take up water very quickly, encouraging you to water them more regularly than necessary, leading to overwatering.

• Underwatering

While it’s not as common as overwatering, underwatering is definitely an issue for some beginner growers (especially those that have been warned about overwatering their plants).

Cannabis plants constantly lose moisture through their leaves in a process known as transpiration (which plays an essential role in a plant’s ability to transport water from its roots up through its stem). Hence, it’s super important they always have access to water from their soil. When a plant goes too long without water, a lot of its vital functions start to slow down. Any roots that dry out completely die off, stunting the plant’s growth or possibly killing it all together (if its root system is underdeveloped).

Unfortunately, the symptoms of underwatering are mostly the same as those of overwatering (drooping and wilting). However, you’ll be able to tell that your plants are underwatered if their soil is bone dry.

HOW TO PREVENT DAMPING OFF

We’ve all been there; your seedlings look perfectly healthy, then suddenly you find them slumped over the edge of their containers. Within 24 hours (or sometimes less), they’ve shriveled up and died.

This phenomenon, known colloquially as “damping off”, is caused by fungi like Pythium, Botrytis, and Fusarium. While these fungi can lie dormant in soil, they grow and thrive in overly wet conditions. Overwatering and high humidity, for example, are some of the most common causes of damping off.

Unfortunately, by the time your seedlings show the first signs of damping off (a limp and discoloured stem), there’s nothing you can do to save them. We just recommend removing the affected seedlings from your grow room or propagator ASAP to avoid spreading the fungi.

To prevent damping off, make sure to keep close tabs on the temperature and relative humidity in your grow space, and avoid overwatering your plants. Also, make sure both your soil and pots drain well.

Finally, to minimise the chance of a Pythium, Botrytis, or Fusarium infestation even further, be sure to always use new soil or sterilise your soil by baking it in the oven until it reaches a temperature of 85°C.

HOW TO AVOID NUTRIENT PROBLEMS

Healthy cannabis plants look vibrant and green, and any sort of discoloration on a plant’s leaves or stems can be a sign of nutrient stress.

Remember, cannabis seeds are jam-packed with nutrients to help get your seedlings through the first stage of their life. Once these nutrients run out, it’s time for you to step in and give your plants the added nutrients they need to veg and flower properly.

• Feeding seedlings

Cannabis seedlings are super fragile and can easily “burn” in nutrient-rich soil. In general, we don’t recommend feeding during the seedling phase. Instead, keep your seedlings chilling in their Easy Start pots until they’re ready to be transplanted and start vegging.

Most blogs and forums will tell you that your plants are ready to veg after two weeks, but that’s far from true; it usually takes about 3–4 weeks from germination for your seedling to use up all the energy stored in the seed, although some plants develop faster than others. But rather than going by time, we recommend you transplant and start vegging your seedlings once they’ve developed at least three nodes and 4–5 sets of true leaves.

• Transitioning to the vegetative stage

Once you’ve transplanted your seedlings into their new pots, give them 3–7 days to adjust. Remember, transplanting is a stressful process, and your plants will need some time to recover from it. Feed your plants too early after transplanting, and they likely won’t take up all their nutrients from their medium, which can cause problems (like nutrient lockout) further down the line.

Once you’re confident your plants have recovered from being transplanted, start feeding them with a mild nutrient solution. An NPK ratio of 4:2:3, for example, is a good starting point for plants just beginning to veg.

• Nutrient burn

Growers usually run into nutrient burn when they feed their seedlings too early or when they transition into the vegetative phase (either because they transplant their seedlings into hot soil or they start feeding with a fertiliser that’s too strong). The first signs of nutrient burn are dark green leaves with burnt tips. Left untreated, nutrient burn also causes leaves to curl upwards.

Luckily, unlike some of the other seedling issues we’ve mentioned in this post, it is possible to remedy nutrient burn. Simply lay off the nutrients for at least one week and water your plants with plain, pH-balanced water. Once your plant starts to grow more healthy, green foliage, slowly dial the fertiliser back in.

Whenever you start feeding your plants, we recommend giving them half the recommended dose of fertiliser during the first week of feeding. This gives the plants time to adjust to their new diet.

• Going organic

At RQS, we’re big fans of organic cannabis gardening. No amount of chemical nutrients could ever compare to the complex mix of microorganisms that exist in organic soil.

When growing organic, the focus is all about building a vibrant soil from the get-go, rather than growing in a stagnant medium and pumping it full of chemical nutrients once a week. While it’s a lot more hands-on, the taste of organic weed is hard to beat. Just remember that organically grown plants typically don’t provide the same yields as their non-organic siblings.

HOW TO PREVENT PESTS AND BUGS

Pests and plagues can destroy seedlings in less than a day. To prevent this from happening, it’s super important to keep the environment around your seedlings clean and at optimal temperatures and humidity levels. Avoid overwatering, and remember to read up on common cannabis pests so you can spot and treat them early. Some common pests to look out for include:

• Fungus gnats

These small, black, fly-like bugs feed off your plants and lay their larvae in wet topsoil.

• Spider mites

Black or red in colour, spider mites live on the underside of leaves and sometimes spin protective webs around healthy foliage. They love hot, dry conditions.

• Leaf miners

These small, slender, winged insects leave irregular snail-trail-like spots on healthy leaves.

• White powdery mildew

As the name suggests, white powdery mildew is a type of mould that forms as a white, flour-like powder on the leaves of your plants.

• Pythium and Fusarium

These fungi can be hard to spot, but white spots on wet topsoil can be an early sign of their presence.

Cannabis seedlings like warm, humid conditions. Unfortunately, pests and diseases also love these conditions. Keeping things extra clean and growing your seedlings in a propagator can help prevent an infestation.

HOW TO PREVENT STRETCHY SEEDLINGS

Seedlings stretch in order to get closer to their light source. To keep your seedlings from developing unnaturally long, flimsy stalks, grow them under blue spectrum CFLs located roughly 5cm from the top of the plants. Also, avoid keeping your seedlings in the dark for 24 hours after germination (a common piece of advice on grow forums), as the lack of light will force your seedlings to stretch abnormally.

KNOW WHEN AND HOW TO TRANSPLANT YOUR SEEDLINGS

Unfortunately, transplanting seedlings is far from an exact science; rather than following a strict calendar or schedule, it’s all about paying attention to your plant and knowing which cues to look out for.

As we mentioned earlier, a good rule of thumb is to transplant seedlings when their leaves fully cover the circumference of their container. After about one week, try checking on your seedlings’ roots. If you can completely remove a seedling and all its soil, it is ready to transplant.

Remember to be very gentle when handling your seedlings and transplanting them. Any minute damage to their roots can result in a ton of stress that, for such young and fragile plants, can take a while to recover from.

GET GROWING!

Now that you know the theory behind growing healthy cannabis seedlings, it’s time to get your hands dirty. Remember to invest in one of our Starter Kits for the best, most reliable results, and keep reading our blog for more tips on growing spectacular weed at home.

Struggling with your cannabis seedlings? Click here for 3 simple steps to growing healthy seedlings, alongside tips for mastering the cannabis seedling phase.