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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.

Common Seedling Problems & Mistakes

Table of Contents

Before we take a look at cannabis seedling problems and common beginner mistakes, let’s show you what healthy cannabis seedlings and young plants look like! If your plants look like this, you’re golden!

Healthy Cannabis Seedlings Look Like This!

Examples of healthy cannabis seedlings:

Cannabis seedlings start with two round leaves known as “cotyledons.” These leaves are already formed inside the seed and simply open up once the seed has sprouted. After the cotyledons emerge, the “true” (serrated) cannabis leaves will start to grow from the center.

As they get older, the leaves start looking more like the cannabis leaf you are probably most familiar with. Here’s what those seedlings look like as they start growing into healthy young cannabis plants…

Now that you know what healthy young cannabis plants look like; let’s take a look at some common seedling problems to avoid so your plants grow as fast and healthy as possible!

Common Cannabis Seedling Problems

1.) Overwatering

Symptoms: seedling is droopy, growing medium is moist, damping off

Most common causes:

When a cannabis plant is “overwatered” it has less to do with the water and more to do with oxygen. Plants can even grow directly in water (hydroponics) but in order to thrive, roots need oxygen. In hydroponics, that’s accomplished by dissolving oxygen into the water. But when plants are grown in a container, too much water = not enough oxygen.

When a plant’s roots are sitting in water, they quickly use up all the oxygen until the growing medium starts to dry out. Without enough oxygen at the roots, the plant will start showing symptoms of oxygen deprivation. Luckily, there are many steps you can take to prevent overwatering your cannabis plants.

While overwatering can display many different symptoms, most overwatered cannabis plants look droopy, like this…

Despite what seems like an obvious cause, several different scenraios can end in overwatering. Here are some of the most common trouble-makers:

Big Pot, Small Seedling

When you have a small plant in a very big pot, it’s easy to overwater because the roots aren’t drinking much yet, and the big container takes a long time to dry out.

Notice how the plants in smaller containers have grown more than the plant that was put in a big container as a seedling. It’s common for plants in too-big containers to grow a little slowly at first.

  • (Recommended) Start seedlings in smaller container until they’re growing vigorously, then transfer to a larger container
  • If seedling is already in a big container, there’s still hope! When watering, give just a little water at a time in a small circle around the seedling. Then allow the top inch of your medium to mostly dry before watering again. Once the plant is growing vigorously, start watering as normal (with extra runoff water coming out the bottom every time)

These small cannabis plants (below) were put in big pots, and were given enough water to support a much larger plant. The plants couldn’t drink all the water that was given to them and as a result, their roots weren’t able to get the oxygen they needed and started “drowning.” Once the roots are out of commission, the leaves start drooping.

One way to prevent this from happening is to make sure your plants are in an appropriately sized container for each stage of their life; this is done with transplanting.

First, you need to get a general idea of the final container size which will be based on how big you want your plants to grow. The less often you transplant, the bigger the final size pot you’ll need because the roots will tend to grow out and cover the whole container if left too long. You can help avoid problems with roots getting rootbound by using a fabric pot (also known as a “Smart Pot”) or an air pot.

Final Container for Desired Plant Size – General guide
(the less often you transplant your plants, the bigger final size you’ll need)

2-3 gallon container

3-5 gallon container

5-7 gallon container

6-10 gallon container

8-10+ gallon container

But what size pot should you use for your seedlings?

For fastest growth rates, it’s better to plant young seedlings or clones in a very small container, like a disposable plastic solo cup.

For new seedlings and clones, use a small container if possible

Easy transplant guide – some popular transplant guideline:

  • Solo cup -> 1 gal -> 3 gal
  • Solo cup -> 1 gal -> 5 gal
  • Solo cup -> 2 gal -> 5 gal
  • Solo cup -> 1.5 gal -> 3 gal -> 5+ gal

There is no perfect transplant guide, but the one above should give you a general idea of where to start.

Why don’t you want to go from a solo cup to a 5 gallon pot? Or why not just start in a 5 gallon pot?

Young plants won’t be growing very fast yet, so they also won’t be using much water. When you completely saturate a big container that slow speed means that the plant won’t be able to drink all the water. Since so much of the water is contained in the middle without access to air, it won’t be able to dry out by evaporation. This means you’re left with a huge container full of wet potting mix.

The young cannabis plant roots will quickly use up all the available oxygen that’s been dissolved in the water, and then the roots will sit in water until the water slowly evaporates on its own. Some containers such as smart pots and air pots allow air in from the sides, which can help dry the growing medium faster, but it’s better to use proper technique from the beginning.

Planting in too big a container is sometimes called “overpotting.” It’s possible to get around this with special watering techniques (for example by giving plants just a little bit of water until they start “growing into” their containers) but starting plants in small containers and transplanting as needed can be a more straightforward way for some growers. Overpotting plants is also a waste of growing medium and nutrients, especially if the plants never get big enough to fully use their containers.

This OG Tahoe Kush seedling was overpotted, though this can be overcome by the grower just giving a little bit of water at a time until the plant starts growing vigorously. At that point, the grower can provide more and more water until they’re finally watering normally.

More information about container size and transplanting here: https://www.growweedeasy.com/germinate#what-size-pot

Small Pot, Big Seedling

While using a too-large container can cause problems for seedlings, so can too-small of a container.

Seedlings are happy in a small container like a solo cup for a while, but as they get bigger, their roots need more room. The roots tend to wrap around the outsides of the container, encasing the middle part so that water can’t get out. This is known as the plant being “root bound.”

If the seedling isn’t transferred to a bigger container in time, it can cause symptoms of overwatering, nutrient deficiencies, wilting, and sometimes very strange and unpredictable symptoms.

These plants were left in a too-small container for too long. Because they were drinking so fast, the grower watered them frequently – too frequently! This combination of being root bound and overwatering caused the plants to suffer.

A too small container, combined with overwatering – these conditions can cause some strange symptoms that often look like a nutrient deficiency

Pink leaves, red discoloration, rusty spots and edges… While it make look like these cannabis seedlings are experiencing nutrient deficiencies, all these symptoms are actually caused by a combination of overwatering plus a too-small pot.

When the roots aren’t happy, the plant isn’t able to uptake nutrients properly and cannabis seedlings can show a wide variety of strange problems.

It’s usually not a good sign when cannabis leaves start “crossing their fingers” like this (instead of having all the leaf tips spread out). While this can happen naturally every once in a while, you know for sure that you’re having a problem if the crossed fingers are combined with discoloration of the leaves. Also notice how the stems are bright red/pink.

The following cannabis plant was also overwatered and had no drainage. Notice how dark the soil is and the green algae growing all along the top of the soil – these are more signs the plant has been overwatered for quite a while. You should never water your plant when the soil on top is still wet, and if you notice lots of algae growing on top of your soil, it may be a sign that you’re overwatering on a regular basis. Leaving the top of the soil wet is also the number one reason growers get fungus gnats.

No Drainage (or poor drainage)

Cannabis roots need oxygen to thrive, and therefore they will have trouble if the roots are “drowned.” If water cannot run out the bottom of the container, it will pool at the roots, which causes overwatered plants.

  • Always start with a good growing medium that drains well – never use a clay based soil which holds onto way too much water. A high quality potting mix (especially mixed with some perlite) provides great drainage
  • Start with a smaller container to reduce the chances of overwatering seedlings
  • Make sure there are plenty of drainage holes to let water out the bottom of the container
  • If water runs through growing medium slowly, you can mix perlite into the potting mix to increase oxygen and quicken drainage
  • Water less often and less at a time until plant is drinking more
  • Get a container that helps the growing medium dry out from the sides (such as “Smart Pots” – highly recommended; or air pots).
  • Don’t allow plants to sit in a tray that has been collecting runoff water

This seedling started “damping off” (dying) due to terrible drainage from bad soil. Never use soil that looks like it contains clay!

Seedling is “damping off” due to bad soil with no drainage

Here’s another example of a seedling damping off due to too much water (drowning roots), whis time combined with not enough light. After a few days of these conditions, this seedling just fell over and started dying.

The following plant was grown in an unsuitable growing medium with no drainage and started showing signs of overwatering. Always start with a quality potting mix that has good drainage, and never allow the top of your growing medium to look this wet!

This “soil” is more like mud. The plant roots are drowning from lack of oxygen, causing severe wilting.

Watering too often

While oxygen is available to the roots immediately after watering, the roots use up all the oxygen quickly if they are sitting in water. If all the oxygen is gone, roots are not able to get what they need to help power growth, at least not until the growing medium begins to dry out and create new air spaces in the growing medium.

Keep roots happy for fast-growing plants

Each air spot in the potting mix provides roots with precious oxygen, but if there’s no air spots, roots start to “drown.” By watering seedlings less often, growers can ensure that roots are getting access to plenty of oxygen at all times.

Of course you should never allow roots to actually dry out – roots need moisture at all times. But for new growers who want to do everything possible for their new seedlings, it can seem like more water = better. Unfortunately, this isn’t true.

Roots work best when they get as much oxygen as possible while also staying completely moist at all times.

  • Wait until top inch is dry. Make sure that the top bit of potting mix has started to dry before you water seedlings again. Sometimes it can take a few days, depending on your growing medium, your environment and how much water you provided during the last watering.
  • Increase the number of air pockets in the growing medium by mixing in a “lighter” amendment like perlite to the potting mix. Perlite will allow the mix to hold onto more oxygen when mixed with heavy soil. Many cannabis soil growers will mix 30-40% perlite into their potting mix to make sure there’s lots of drainage and plenty of air available for the roots.
  • Provide air from the sides. Transplant to a container which allows air in from the sides like fabric pots (“Smart Pots” – highly recommended) or air pots.
  • Start in a smaller container until plant gets bigger so there’s less water in the potting mix that needs to dry. You’ll be able to water your plants more often while ensuring they get plenty of oxygen.
  • Water less when it’s cold. Plant processes tend to slow down when temps get cooler. This means that plants usually need water less often than normal after a cold snap.

This plant went through a few cool days but the grower continued to water as normal. As a result, the plants roots were surrounded by too much water and the plant started showing signs of overwatering.

The plant was watered the right amount each time, but too often. As a result, it shows some slight drooping. While this won’t kill the plant, the plant will definitely grow faster when the mix is allowed to dry out a bit so the roots are getting plenty of oxygen.

2.) Underwatering – seedling is droopy, wilting, or not growing properly, and the growing medium around the seedling isn’t moist

While overwatering is the most common seedling symptom, underwatering is also a problem, especially for those who have been warned to avoid giving too much water.

It can be confusing because the symptoms often look similar to each other, which is why it’s important to learn good watering practices.

This seedling was underwatered – the grower had been warned many times to avoid overwatering, and went too far in the other direction. Notice that the growing medium looks bone dry.

It’s crucially important to make sure that plant roots have access to moisture at all times. Plants are constantly losing water through their leaves (called “transpiration”) and this is actually how plants get water up from the roots. As the plants lose water from the leaves, it pulls water up from the ground like a straw.

When there’s not enough water at the roots, many plant processes cease to function. If roots actually dry out, the dried shoots die.

Here’s another example of a young cannabis plant that is underwatered, even in a big container (where the problem is usually overwatering). Notice how this cannabis seedling is basically just wilting and falling over, while the potting mix looks completely dry.

Seedlings suffer greatly from being underwatered, even more so than from overwatering. Often the grower will actually be able to see how dry the growing medium is. A big sign that the plant is being under-watered is when you can see the soil separating from the container. In this case, you can see the starter cube separating from the soil because it’s so dry.

Underwatering is bad on it’s own, but it causes the most problems when young cannabis seedlings are also stressed by too high levels of nutrients, or when started in a “hot” (nutrient-enriched) soil.

When underwatering is combined with too much nutrients, seedlings often become dark green and stunted, with twisted and discolored new growth.

The solution for this (underwatering + high levels of nutrients) is simply to give the plants more water so they can establish roots and start growing again. Most plants will be able to grow out of this problem once they get enough water to start growing. While it’s not always the best idea to start out with a hot soil mix, most seedlings will easily grow into it if given a good growing environment.

This cannabis seedling is dark because it was underwatered in a “hot” soil mix, but after watering the plant as normal for a week or two, the plant started growing vigorously

3.) Nutrient Problems – leaves are yellow, discolored, crispy or have spots

Healthy cannabis leaves on seedlings should be green! Again, here’s what healthy leaves look like.. .

Healthy Leaves Look Like This

When the cannabis leaves of young plants stop being green, you need to react. Changes of color (such as yellowing, spots, burnt tips, etc) are usually a sign that there’s a problem when it comes to young cannabis plants.

The leaves of young cannabis plants & seedlings should be green!

Some common seedling nutrient problems include…

Too Much Nutrients

A nutrient toxicity is most common in dry or hot conditions, when starting in “hot” soil, and when plants are underwatered.

Two of the most common signs of nutrient toxicty are tip burn and dark leaves.

Tip burn is a sure sign that the plant took up too much nutrients

A closeup of nutrient tip burn

Nutrient burned tips eventually start curling upwards if nutrient levels are too high for too long

Very dark leaves often indicate a nitrogen toxicity (too much nitrogen)

If a nitrogen toxicity is left too long, it starts causing other nutrient problems, like the yellow lines on the bottom leaves of this plant.

Causes of Nutrient Toxicity

  • “Hot” Potting Mix – Sometimes seedlings get a nutrient toxicity when started ing a “hot” potting mix (one that has a lot of nutrients). If it’s good soil and you’re watering properly, your seedlings will be able to grow out of this relatively quickly.
  • Slow-Release Soil – Nutrient toxicities are common when grower start with a “extended release” soil like Miracle-Gro original soil – you don’t want any type of soil that will be slowly releasing nitrogen throughout the grow; it will cause nutrient burn and reduced bud development in the flowering stage. Avoid original Miracle-Gro soil and any other slow-release soils!
  • Give Nutrients Too Soon – Giving nutrients too early will overload the seedling with nutrients – in a good soil potting mix, additional nutrients usually aren’t needed for the first few weeks at least
  • Give Too Much Nutrients At Once – Giving too much nutrients at once can cause a toxicity overnight – always start at half the recommended dose according to the nutrient schedule (most cannabis nutrients come with a nutrient schedule), and see how your plants react before upping the dose

Too much nutrients too soon caused this (tip burn)

While the above seedling may look light colored, the problem is actually that it was given too high levels of nutrients.

When there’s too many nutrients, the plant can start getting light colored because some nutrients are getting locked out. The tip burn on the leaves is a good indicator that this problem is caused by too many nutrients. Also this grower started with a “hot” (nutrient rich) soil mix, and there’s no way a plant this size could have already used up all those nutrients.

A lot of growers may think the way to fix this is add more nutrients since the plant leaves are pale, but that will actually make things worse! This plant just needs some plain water until it starts to use up the nutrients in the soil, and it will soon take on a healthy green appearance on new leaves.

Not Enough or Wrong Kind of Nutrients

Nutrient deficiencies and other nutrient problems are most common when growers are using the wrong type of potting mix or cannabis nutrients.

Two of the most common signs of nutrient deficiencies are pale or yellowing leaves and other unusual leaf discoloration.

The most common type of deficiency is a nitrogen deficiency.

The yellow leaves of a nitrogen deficiency may show signs of brown, and they will usually become soft and sort of “fold” in, before turning crispy and falling off on their own.

If the yellowing leaves are at the top of your plant or the yellow leaves are mosty new growth, then you probably don’t have a nitrogen deficiency. Nitrogen deficiencies affect the oldest, lowest leaves first.

Nitrogen Deficiency Leaf Closeup

There are many other nutrient deficiencies, and you can view them all here…

Causes of Nutrient Deficiencies and Problems

  • Soilless Medium w/o Hydro Nutrients – Some growers may start in a soilless medium and not realize it has no nutrients (with a soilless medium like vermiculite, coco coir, pertlie, rockwool, etc, it’s up to the grower to provide all the nutrients since they are inert mediums and don’t contain any nutrients on their own) which results in a deficiency if grower isn’t providing extra nutrients. Soilless mediums are easy to grow in, but they do require the grower provide nutrients from the beginning.
  • Don’t Provide Nutrients As Plant Uses Up Soil – Many growers start in a good soil that has nutrients, but don’t give nutrients or transplant seedlings to a bigger container when the plant has started to use up the nutrients in the soil
  • Wrong Type of Nutrients – Nutrient deficiencies commonly show up with the grower gives their plants the the wrong type of nutrients – generally it’s a good idea to give a “vegetative” nutrient formula for the first part of the plant’s life and a “bloom” nutrient formula for the flowering/budding stage. When giving the wrong time of nutrients at the wrong time, your plant won’t grow as well. If you give vegetative nutrients in the flowering stage, you make it harder for the plant to form buds, while also increasing the chance of getting nutrient burn and other nutrient problems.

Other Nutrient Problems

  • Not Maintaining pH – If growers don’t manage pH, their plants may show signs of nutrient deficiencies even if the nutrients are actually there near the roots.
  • Improper Watering Technique – Growers who don’t water properly (growing mediums stays wet or dry for too long, poor drainage, etc) often start getting nutrient deficiencies as the plant isn’t able to effectively carry out normal plant processes
  • Too Small Container – Nutrient problems crop up when plants are kept in a small container for too long without being transferred to a bigger pot (this is known as being “root bound” and can cause the plant to display nutrient deficiencies because the roots aren’t functioning properly)
  • Bugs– a lot of bugs and pests may initially look like a deficiency (spots on the leaves can appear from bites, or if bugs have infested the soil, etc)

4.) Heat – leaves bend in the middle so they look like canoes or tacos, turning up at the edges, wilting, strange spotting, symptoms usually appear after temperature starts climbing.

When the heat gets too high, the edges of the leaves will begin to curl up and the leaves will begin to “cup” or “taco.”

Here’s another cannabis seedling suffering from heat stress – notice how the edges are curling upwards. The solution to this problem is simply to lower the heat as experienced by the plant.

Sometimes the leaves sort of fold downwards due to heat, too, like this seedling

After being subjected to overwatering plus a heat wave, the leaves of the following seedling started cuppping upwards and turned lime green. The stems and veins of the leaves were turning red. You can see the soil is still dark and wet because the plant stopped drinking after developing root problems.

Cannabis plants often display heat stress when grown in hot, dry weather, especially when not given the right amount of water.

Learn more about cannabis heat stress and how to fix it: https://www.growweedeasy.com/heat-light-stress

5.) Not enough (or too much) light – burned or crinkled leaves, too much space between nodes, tall seedlings that fall over

Not Enough Light = Stretched, “Leggy,” Tall Seedlings

Too Much Light = Burned, Crinkled Leaves

Stretched, “Leggy,” Tall Seedlings – Give More Light!

This seedling is stretching too tall, with a lot of space in between sets of leaves, and a long thin stalk. This is caused by the plant not getting enough light. It’s “reaching” upwards, trying to find the sun.

More seedlings stretching from lack of light

To fix too-tall seedlings, simply provide more light (usually by bringing grow lights closer or getting a brighter grow light)

After giving enough light, growers can bury the extra stem, or just wait until the seedling grows out of it on its own

Burned, Crinkled Leaves – Reduce Light or Move Grow Lights Up

This cannabis seedling basically grew up into the grow light!

This cannabis seedling is being burned by too-close LED grow lights

FAQs – Frequently Asked Questions

Question: What do seedlings like?

Answer: Moist but not drowning conditions, warmer temps, and a bit of light to help them start growing. Very little nutrients to start.

Question: How do I avoid germination problems?

Answer: Before anyone worries about cannabis seedling problems, it’s important to get your cannabis seeds to sprout!

So make sure you are avoiding these common germination mistakes!

Most importantly, just remember that cannabis seeds like a warm, moist environment to sprout.

Common Germination problems

  • Too wet – don’t drown your seeds! While it’s okay to soak seeds for the first 24 hours, after that they should be moist but not soaking.
  • Too dry – if seeds are too dry, they won’t sprout! If seeds sprout but then are exposed to dryness, they will die.
  • Too deep – if you plant seeds too deep in the growing medium, they may have a hard time making it to the surface. An inch deep (just enough to support the seed and cover it) is about as deep as you’ll ever need to go.
  • Not warm enough – seeds and seedlings like warmer temps (from 80-85 F) and will grow more slowly in cooler environments.
  • Wrong starting growing medium – Many growers like to plant their seeds directly in a growing medium, just like in nature. But some growing mediums are better for seeds than others. Learn more about the pros and cons of different starting growing mediums here.
  • Old or improperly stored seeds – any seeds that germinates is a good seeds, but older or improperly stored seeds often take longer to sprout, and may no sprout at all, even if you do everything right.
  • Not ripe seeds (pale or translucent) – while any seed that sprouts is a good seed, seeds that are pale, flimsy or translucent have very low germination rates because they’re not fully mature.
  • Too much humidity – Some growers like to use a humidity dome for new seedlings, but don’t leaves these on too long after sprouting, as too much humidity can cause “damping off (seedling sort of folding over and dying, more info below)

Question: Am I drowning my plants? I planted my seeds two days ago in moist soil, I watered them a little, but no waterlogging. I then stopped watering them for fear of drowning them. Today, the top of the soil is getting dry, there’s still some moisture left in it, but not much from what I can tell. Should I keep it moist or just leave it be?

Answer: Young seedlings can get easily drowned, especially in a big container (learn about different containers for growing cannabis). But at the same time, they like moist conditions, and seedling roots should NEVER dry out as this can kill or seriously stunt your plant.

But how to balance the need for both water and air?

In a smaller container like a solo cup, it’s very difficult to overwater young seedlings as long as there’s plenty of drainage and you’re using a good growing medium. Once seedlings have started to outgrow a small container, you can transfer to a bigger container and the seedling will be much more robust.

If you’ve started your seedling in a big container, it’s good to be worried about overwatering young seedlings. In a large container, it generally takes a relatively long time for the growing medium to dry out, and your seedlings aren’t drinking much. Therefore it’s easy for them to get waterlogged. In this situation, you can use a spray bottle or a mister to mist the area around the plant thoroughly, which will seep down to the roots and keep them wet, but won’t soak the soil. Another option is to use just a small amount of water, maybe a cup at a time, and water in a circle around your plant until it starts growing vigorously. Giving seedlings just a bit of water at a time prevents them from getting drowned in drenched soil.

Once the plant is growing fast, you can start watering as normal (water until 20% runoff comes out the bottom, then don’t water again until the top inch is dry to the touch). At this point your plant will be drinking more and will have a stronger root system to seek out both the water and the oxygen it needs.

After reading this article, all your seedlings will look as green and happy as this one!

Common Seedling Problems & Mistakes Table of Contents Before we take a look at cannabis seedling problems and common beginner mistakes, let’s show you what healthy cannabis seedlings and