Causes of death in plants during the growth period

Causes of death in cannabis plants during the growth period

The vegetative growth of cannabis plants can be one of the longest periods of cultivation when growing outdoors - or indoors - where in, for example the countries of southern Europe they enjoy a lengthy spring and summer. During the course of this growth phase, problems can arise that may lead to the death of the plant even before the flowering stage begins.

Let's see what are the most frequent causes of death during the plants' growth period and what we can do to avoid a premature, unhappy ending.

Cannabis plants in growth period
Cannabis plants in vegetative growth

Overwatering cannabis plants

The most common cause, especially among beginner growers, is undoubtedly overwatering. The excess of irrigation particularly affects young plants in their first weeks of life (although it can also occur with larger plants).

The main reason is watering too much, too frequently. Small plants have a very limited resistance, partly because of their size. A plant with two cotyledons and three small roots can not cope with large amounts of water, simply because they can not process it, not having sufficient absorption capacity in the root zone.

The growth phase is crucial for an abundant bloom
The growth phase is crucial for an abundant bloom

If we overwater our plants, the substrate will be permanently wet, meaning the roots will not get enough oxygen and they can begin to rot, falling prey to various fungal pathogens that are capable of killing the plant in just a few days. Depending on their genetic inheritance, there are varieties that are are better or worse adapted to withstand an excess of irrigation, for example Afghani genetics such as Northern Lights; originating in a dry, arid climate, they can not tolerate continuous moisture in the root zone. On the other hand, cannabis plants with tropical ancestors will tend to have a greater resistance to root rot, as in the case of the world-famous Skunk.

To avoid a plant suffering from excessive watering during its cultivation, first we need to be careful not to swamp the substrate. If this happens, let it dry before watering again. Avoiding heavy substrates with too much clay will also help, remember that the roots also need oxygen!

A long period of wetness in the substrate means that the roots can't transport food to the upper parts of the plant, which will feed from its nutrient reserves, causing the smaller leaves to lose their colour gradually, from a pretty green to a yellowish shade.

Excessive irrigation in a seedling
Overwatering in a small plant

Once the leaves of the plant change to a yellow colour due to excessive watering, root rot will often come next, and with it the consequent death of the plant. Another symptom of possible overwatering is if the plant appears to be wilted (with droopy leaves) even though the substrate is moist.

The most harmful fungal pathogens for cannabis plants

Pythium, Fusarium and Phytophthora are the 3 most harmful moulds to cannabis plants, capable of killing them in a very short time and with almost no possibility of treatment. Prevention is always the best method to combat these fungal pathogens.

Healthy roots vs rotting rots
Healthy roots vs rotting rots

These fungi come into contact with the plants via the roots, usually due to root rot or any decomposing organic matter such as the fallen leaves of the plant that remain on the soil surface. For this reason it's important to remove any dead leaves from the substrate where they could cause a fungal infection.

Another way to protect the roots against fungal attacks is through the use of microbials, with the fungus trichoderma. This type of microbial life protects the roots while optimising nutrient uptake to the plant much more effectively than in a lifeless substrate.

This beneficial fungus colonises the roots and leaves no room for harmful fungi to settle on them, and if they do, the trichoderma takes care of eliminating them. This type of microbe can be used any time from germination until harvest, although ideally we'd use it from the beginning and maintain it in good conditions, or keep adding it with each transplant. Using sugars and carbohydrates helps the micro-life to stay active throughout the grow.

Botrytis at the tip of a lower branch
Botrytis at the tip of a lower branch

Drought or under-watering

A lack of water, or drought stress is another of the principal factors  that can seriously affect plants and cause premature death. The plants require water for their survival, and if they run out of it for a few days or even hours (depending on the cultivation system) they can die very easily.

Even if the plant manages to survive the drought period, it's inevitable that part of the root system will be affected. When part of the root system dries out and dies, it is usually accompanied by some of the leaves and branches, which will weaken the plant and reduce it's capacity to process nutrients, impacting negatively on development and translating into a smaller final harvest.

Lack of water led to this plants death
Lack of water led to this plants death

If this period of drought is repeated or is too prolonged, the plant may not be able to survive as well it could the last time, as its root system is now much less extensive than it was initially. Remember that you can use products to stimulate root growth, helping the plant to develop more roots and therefore feed more efficiently and more able to tolerate any periods of drought.

Lack of light in the grow

Although it is not very common in outdoor gardens, where fortunately the sun is always present, in indoor cultivation a lack of illumination could occur for various reasons: if we have a blackout, a bulb fails, the timer doesn't work properly, the ballast stops running unexpectedly or if we have some other problem with the electricity supply or our installation.

Cannabis plant after 2 days without light
Cannabis plant after 2 days without light

In this case, the plants can last for a few days without light, although they will be greatly weakened  and more likely to experience possible rotting of roots and leaves if the humidity in the grow space is high. Initially, the upper leaves will take on a yellowish color due to a lack of chlorophyll, as the plant can't carry out photosynthesis properly.

Too much light in the grow

Lights that are too powerful or too close to the plant can dehydrate the leaves, curving the edges upward (indicating a lack of transpiration). When the stomata - which are small holes in the leaves where the plants breathe - close, the plants can not "breathe" properly, and if we add to this a very low humidity, they can dry out quickly and end up dying. Therefore, it is vital to carefully select the proper type of lighting for a cannabis grow.

Lack of transpiration due to low humidity
Lack of transpiration due to low humidity

Excess of fertilisers, nutrients or salts

Plants require food to be able to grow, but an excess of fertiliser could kill the plants if we don't take quick action to remedy it.

Organic fertilisers don't tend to over-fertilise plants because they release nutrients slowly. If using mineral fertilisers for cannabis, this possible problem must be taken into account if we want to avoid problems.

To find out if the substrate has an excess of mineral salts, we need to monitor the EC of the drainage water. If the runoff comes out with a similar EC to the inlet (the one used for irrigation) then everything is correct. However, if the EC of the drainage water is much higher than the inlet water, a root-flush should be performed to wash the excess salts out of the substrate. Using enzymes in each irrigation helps keep the substrate free of salts.

Insect infestation

Insect pests can be many and varied, and although not all are 100% fatal to the plant, many of them are capable of devastating our garden if they're not treated properly. Of course, it's always possible that the plant will survive the infestation, but a serious insect attack will almost always lead to weak plants and lower yields.

One of the most feared insect infestations is the stem-boring caterpillar, which eats into the central stem and hollows it out. The flow of the sap is obstructed, halting growth and after a few days the plant ends up wilting and dying. It can be very difficult to detect with the naked eye and to find it you'll need to look for holes in the stem, usually beneath the nodes of the non-woody parts which have more tender vegetable tissue that's easily edible by the caterpillar.

Insects can quickly ruin your harvest if not treated properly
Insects can quickly ruin your harvest if not treated properly

Red Spider Mites are also one of the most common and devastating pests if not treated in time. In addition, their eggs can remain dormant for a long time, ready to hatch and infect the crop again when the conditions are right for their development.

Snails and slugs can be very harmful when the plants are very small and don't yet have a lot of leaves. If the plant only has 4 leaves and these small devourers eat them, it will not be able to transpire or capture solar energy for photosynthesis, which can seriously compromise its development.

Insect damage on cannabis leaves
Insect damage on cannabis leaves

Fungus gnats, nematodes, aphids, or any root-feeding insect can cause the plant to lose its vigour during the growth period, meaning that the flowering phase can be seriously affected.

Extreme temperatures: hot y cold in the grow

Extreme temperatures - both cold and hot - can be lethal to plants. In winter, the cold can be controlled using radiators indoors, and even in outdoor cultivation through the use of greenhouses.

Keep in mind that if the temperature drops below 12ºC, the plants may die. From 12 to 16ºC the plants growth is halted as they become dormant, as if they were hibernating, but essentially what they do is completely slow their metabolism down to keep alive while waiting for the climate to improve.

Cannabis in cold conditions
Cannabis in cold conditions

A temperature lower than 12ºC can kill the plant in case of prolonged exposure and it is not remedied. They can also die by freezing when the temperatures get as low as 0°C.

On the contrary, extreme heat is another factor that can cause the plant to die. Although it is less harmful than the cold, it also ends up severely affecting the development of the plant in all its stages of life, hindering its transpiration, nutrition and cellular development.

With high temperatures the roots can be "cooked", for this reason when growing outdoors we recommend using white pots instead of black, and if possible to cover them from the direct impact of the sun using insulating material.

Indoor grow tent with temperatures up to 40ºC
Indoor grow tent with temperatures close to 40ºC

Dehydration is very common in high temperatures, since the humidity of the substrate will evaporate more quickly, the roots dry out, the stomata close and the plant cannot transpire and will not develop with the proper vigour and vitality.

To fight against extreme temperatures in an indoor grow, air conditioners or radiators can be used. In the case of an outdoor crop, you can use greenhouses against the cold and shading mesh to protect plants from the suffocating heat of summer.


These are the most common causes of death in young cannabis plants. Remember that depending on the case, this can happen in a very short time and if we don't take action, the plant most definitely will end up dead.

It should be noted that, although these are the most common causes, they can occur with greater or lesser ease depending on the growing conditions that the plants have to endure. Of course, if a substrate is used that is not suitable for cannabis cultivation (such as field clay), problems with the roots may be more present than using a suitable substrate for cannabis.

Cannabis plant in a clay soil, completely unsuitable
Cannabis plant in a clay soil, a completely unsuitable substrate

A lack of ventilation in the cannabis grow space can facilitate the appearance of fungi due to stale air and excessive heat in the environment, as well as a lower evaporation of moisture from the substrate. In turn, this encourages the possible appearance of insects such as white flies or fungus gnats, in addition to promoting the appearance of fungal pathogens such as botrytis, pythium or fusarium.

In many cases, where problems discussed in this article arise in the grow, it is usually due to poor management of the environment or not taking into account the needs of the plants when selecting the appropriate substrate or fertiliser. One simple error in a cannabis grow can cause the appearance of other problems that are even more devastating, so for this reason it is important that all aspects of the crop are well under control before starting out on the grow adventure, and avoid nasty surprises such as the premature death of your plants.

Happy growing!

Comments in “Causes of death in plants during the growth period” (9)

Hello Please can you help, I have 16 plants growing in a tent using hydroponic techniques . The problem i have is that one out of the 16 plants is wilting while the other 15 seem healthy, This has occurred a couple of times. Any advice would be grateful. Thank you
Tim Alchimia
Hi John, sorry to hear about your plant wilting. Without being able to see it, I'm guessing it's happening because that particular plant either isn't getting enough nutrient solution or it's getting too much irrigation, which is causing root problems and possibly fungal issues. You said this has happened to you before, so is it always the same position in the hydro system that is affected? I would check the dripper lines and ensure that there isn't a blockage preventing the plant from being irrigated, or for a damaged dripper that could mean the plant is getting too much water. Also, check the condition of the roots, they should be white and thick when they're healthy. Stringy, yellow/brown roots indicate a problem. I hope that helps, best wishes and happy growing!
So I just started an auto flower grow in my window seal but moved them to an indoor grow but I started 5 an overtime each plant would just gradually fall over then shrivel off an die so far 2 have died and a third just started to falling over (2 felling while living in window seal)
Tim Alchimia
Hi Nathan, thanks for your comment. I'm sorry to hear that you haven't had much luck with your seedlings. It's hard to know what could have gone wrong without more info, but I can try. Does the window sill get full sunlight all day long? It could be that the seedlings are stretching too far to reach the light and falling over as a result. Conversely, it's always possible that the seedlings have got far too hot on the window sill, and the shrivelling up is due to heat stress. A thermometer/hygrometer will help you to work out if the window sill is too hot or not. Other possibilities are overwatering, which can easily lead to a condition called "damping off" aka fungal pathogen Pythium. If you check out our blog post on the subject, it may help you to identify the problem and prevent it from happening in the future. Any more details you could give us would be very useful in determining the cause. Best wishes and happy growing!
I recently attempted container growing and it was a complete failure. My plants typically stop growing after a week, followed by crunchy yellow/spotted leaves. I know my problem is the roots but cannot figure it out. Fine roots circled the bottom of a solo cup and the plants were not stable to transplant when they stop growing,weak at the stalk-root junction,but I transplant anyway and get another week of growth yet roots are not developing ,barely elongating downward,not lateral and still very very fine. I just checked my organic soil pH and it appears in range,(if we can trust a 25 minute slurry soak tested with pH drops, allowing for whatever sediment passed through the coffee filter to settle,the color matches 6.5ph)My temperatures are in the 80s and humidity is low but plants look amazingly healthy up top aside from some twisted and pale new growth that always straitens out. I did raise humidity with wet towels for a couple weeks,and lowered temperature below 85 and got less growth than ever. The bottom leaves get crunchy and die. The main stalks are thin and woody until the first node ,then thicker up top where they are not woody. Purple coloration has come and gone on some plants. Most seedlings appeared purplish, some looked blue but I'm using "Clackamas coot" soil recipe and shouldn't have Phosphorus deficiencies, especially since there's only a purple petiole here and there with bigger plants. My medium is 33% rice hulls and I began waiting for plants to sag before watering to make sure I wasn't over watering (I wasn't). The plants range from average to dark green with no signs of heat or nutrient burns,and always perk up within hours of watering,but do not grow. The only way I've been able to bring these tiny compacted plants to harvest is to continually repot, sometimes in the same pot sometimes bigger, sometimes smaller, it does not matter,the roots will not develop, still as frail as the first week. They are all tiny and only the male stretched at all after I bloomed them. I was able to pollenate and can see big white seeds busting out of the calyx but I'm afraid even their development has been halted and I won't even get any viable seed out of this 5 month long failure. Yes,I have uncropped plants 5-7" tall planted last November. I was certain it was low pH but my test and having followed everyone's recommendations (2 cups of calcium vs 1 for the acidity of the peat). Why won't my plants grow? It pains me only that one of these plants, the smallest one, would have been a keeper, putting off the crazy rich sour skunky smells that do not exist in today's market,but it never got big enough to take cuttings from. It also pains me that I now live in the Sonoran where guerilla growing is no longer an option,and where there is limited availability of acceptable Cannabis. Will I ever figure out indoor container gardening? Should I pray to the Rhizome gods?
Tim Alchimia
Hi Fredo, thanks for your comment and question. It sounds like you're doing everything right so I wonder what the issue is. Has this only happened with your last grow cycle? Or is it a problem you've had with previous attempts? Just checking that it couldn't be this last batch of seeds or clones that might be lacking vigour. If you started with clones then it's always possible that they came with uninvited visitors, for example, root aphids. These are hard to see, even harder to eradicate and can cause some serious problems to your plants. If you're sure about your source of clones or seeds, then the next thing to do is to eliminate possibilities, so try a good quality soil mix from a grow shop and do a side-by-side comparison. From what I'm reading about rice hulls, they are very effective at reducing soil acidity, so if you're also adding lime then maybe the issue could be too low acidity. Have you tried adding any microbial inoculant products? A good quality mycorrhizal supplement can make a huge difference to plant health and vigour. That's always my go-to if I suspect an issue with the roots. It won't help much with any insect pests down there, but it will improve soil health and help the plant to uptake nutrients. On another note, I don't think that constantly re-potting the plants will help them develop faster. If anything, the stress of transplant will hold them back. I always feel like it takes my plants a week or so to recover from transplanting and get back to vigorous growth again. Sorry that I can't offer much more advice at this stage, maybe a bit more information about the genetics you're growing could help. Till then, all the best and happy growing!
Why is my plants leaves wilting and dying at the top only ?
Tim Alchimia
Hi Jackie, thanks for your comment. I'm sorry to hear your plants are wilting. It's going to be difficult to diagnose the issue with such little information, but these things are usually caused by over-watering, so I'd double check that as a first measure. If that doesn't do the trick then if you can provide any further information I'll try and work out what the problem is. Best wishes and happy growing!
Thank you for your fast reply ! Yes that was my question and yes it goes well without liquid fertilizer. I only added mycorrhiza at the beginning. But i think that if i do this with a non-auto variety i'll have nutrition problems.
Hi, I have a question about indoor growing. I use plaxon light mix soil, for a autoflowering variety. Do i have to rinse (2 weeks before harvest) even if i didn't use liquid fertilizer ?  Thank you 
Tim Alchimia
Hi Don, thanks for your question. So, to clarify, you've not been using liquid fertiliser but instead just irrigating with plain water throughout the plant's life? Just out of curiosity, how did that go with light mix soil? Did you experience any nutrient deficiencies? If I were you I'd simply carry on irrigating with plain water right till the end, because if I've understood you correctly, you've effectively been flushing the plant throughout its life so there oughtn't to be any fertiliser residue in the substrate at all at this point. I hope that's some help, please let me know if I've misunderstood your comment. Best wishes and happy growing!
Clearhead Fred
Up until a year+ ago I had beautiful grows. Then instantly a grow went bad in bloom mode. Plants all yellowed with variying types of lear damage visible. Wayyy to many possibilities. Since that grow NO plants will grow any bigger than 2" to 6" and die off. Doesn't matter what strain. Tried four different soils. Completely tore down to all walls in the rooms and put up all new OSB, plywood, flooring, a light bleach mix sprayed all over heck and creation. Rooms set idle for two months. I stsrt dcdomecseeds. Seedlings came up ok. Got to 2" and stopped growth. Never got past the initial two leaves. This was within 10 days of coming up. If you can think of it, probably has been looked at. Once again it does not matter what strain. RO water to creek water to another well Nope. What could possibly be in the air itself within our home tjat could be doing this. Closing the stomato so it can't breathe which in turn no uptake and then death. We've done the pythium attack. You make it. Your input? No it's not nute lock. Lol
Tim Alchimia
Hey Fred, thanks for your comment. I'm really sorry to hear about all the trouble you've been having there. That sounds dreadful, there's obviously something seriously wrong for plants to die after such a short time. Have you checked with a microscope for mites? I know there are some microscopic mites that can cause chronic infestations and are very, very difficult to get rid of, even with all the measures you've taken. That's really the only thing that occurs to me here if you've looked at everything else. The only other thing to do is to think back to that time roughly a year ago when things began to go wrong and try to remember if there was anything that changed from normal, not just in the grow itself but in the rest of the building and the surrounding area as well. Is there any way you can check the air quality in your home? Something must have changed to cause such a marked difference in results before and after. I'm sorry I can't shed any more light on the subject, but I'm really curious now. Please let us know if you make any progress. Best wishes and good luck!
I accidentally pulled my stem up I replanted but its wilted what should I do??
Tim Alchimia
Hi Candace, thanks for your question. Sorry to hear about your unfortunate accident, hopefully, the plant will recover. I'd be irrigating with some kind of kelp solution to help the plant deal with the stress of the "transplant", and a root stimulant to encourage new roots, but its survival will depend on a few factors, such as how badly the roots were damaged and how big the plant itself is. If it's a small, young plant with few leaves then it can recover quite fast and get back to normal. Of, however, it's a larger plant with lots of foliage it will have a harder time recovering because more leaves mean more demand for water, which the damaged roots can't keep up with. You can help by removing some leaves, which will put less strain on the recovering roots (when the plant wilts it is telling you that the water available to it isn't sufficient to keep the leaves alive). I hope that helps, all the best of luck and happy growing!
Natasha Crayton
Greetings, My cannibis plants have been leggy for a long time. They are a few months old and have not flowered yet. Can I top off stem with new soil or will it rot or erode the stem?
Tim Alchimia
Hi Natasha, thanks for your question. Firstly, yes you can certainly pile more soil around the stem if the plants are very stretchy. As long as the soil stays moist and isn't water-logged then there shouldn't be any problems with the stem rotting. Some varieties will readily grow (adventitious) roots from their stem, while others will find it a bit more difficult. An application of beneficial microbes such as Trichoderma will help to keep any pathogenic infections at bay. However, If your plants are still in vegetative growth and you're concerned about not having enough headroom, you could always try pruning or training your plants to control their height. You say your plants are a few months old but haven't flowered yet... are you growing indoors or outdoors? If indoors, are you waiting for a certain time before switching them to a flowering photoperiod? Choosing the right moment to flip to flower is crucial if you want to make the most of the grow space, too soon and they stay smaller, not taking full advantage of the headroom, whereas if you let them grow too big during vegetative growth they will outgrow the space available to them. I hope that's some help. All the best and happy growing!

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