Common cannabis plant problems and how to solve them

Published Sep 30, 2019 11:00 a.m. ET
iStock / Yarygin

If you are relatively new to the idea of growing marijuana or don’t have anyone to ask the essential questions that can ultimately impact your chances of a successful yield, then this is the place for you. Cultivating cannabis plants is very different than your average houseplant, and despite its reputation as a hardy species, it too has weaknesses that can be challenging to overcome. Some of which can be avoided with time, while others are a natural presence that is nearly impossible to see coming. That is why it’s a good idea to arm yourself with the basics of what to look for in a sick marijuana plant and exactly how to tackle the issue at hand to avoid unnecessary damage as soon as possible.

1. Marijuana plant seedlings dying

Cannabis seedlings are incredibly fragile, which is why it is not uncommon to find entire online threads dedicated to the topic of losing expensive seedlings to some mysterious and unexplainable fate. There are a few common mistakes that first time growers make which can lead to this kind of result, and they are:

Cold environment
Often caused unintentionally by air conditioning units or open windows late at night.

Bad seeds
If you’ve bought a cheap pack of pot seeds online, then chances are they might be old and weak, which will automatically lower your odds of getting one to a mature stage. This can be avoided by purchasing your marijuana seeds through authorized and regulated vendors, or someone that you know and trust with a few extras on hand.

Soil too wet
Though small marijuana seeds definitely do best in a moist and warm environment, too much water can lead to a condition called root rot, where the seedlings will appear healthy until they suddenly flop and become all dried up. To get around this common cannabis problem it’s always a good idea to water more frequently rather than in large amounts and to use pots with drainage holes, and soil that will allow for a healthy flow of any unnecessary liquid.

Not enough light
If you’ve found that your marijuana plant has shriveled up, it is either not getting enough water, or need more light. A lot of first-time growers make the assumption that light isn’t necessary for the first stage of life, and while the process of germination can occur in darkness, the moment those fan leaves begin to appear, sufficient amounts of light becomes absolutely necessary.

2. Marijuana seeds won’t sprout

If you have tried a few different methods to get your weed plant seeds germinating with no success, it is likely due to the age of the seed or the storage of it before it was purchased from a vendor. There are a few helpful tricks for getting marijuana seeds to sprout, but none of them is a guarantee of success. Seeds that are too old will never survive no matter what is done to them, so these ideas should only be used as a last resort.

Soak them in water
One of the most popular methods of germinating difficult seeds in through soaking. Simply drop your marijuana seeds into a small container with lukewarm water and wait for 3-6 hours. Then finish geminating as usual by planting them into soil or placing them into a wet paper towel.

Use sandpaper to thin the shell
Thin grit sandpaper is best, as it will cause the least amount of damage. Slowly scrape away the outer layer until the entire seed has a fresh white color. This idea can also be performed alongside the soaking method for really hard to germinate marijuana seeds.

Provide a hot and humid environment
No matter what you might have heard, the marijuana plant is a finicky sort, and some strains only do well in a tropical environment. The absolute best conditions for germination include a humidity of around 30% and a temperature of over 24°C. While that might not be obtainable depending on your situation, it’s a good idea to replicate that kind of situation as closely as possible for the best chance of success.

3. Spider mites and other natural pests

If you’ve noticed that your marijuana plant is covered in small webs or crawling insects, then you are probably already past the point of what is called an infestation. At this time every moment counts, as many of these tiny critters will either gnaw at the leaves leaving tiny holes in their wake, or the webs will cause damage, and either one is unwanted or threatening for a marijuana plant. To treat these annoying pests, there are a few things that you can do, including:

Dish soap spray
Add 5-10 drops of dawn dish soap to a spray bottle and soak your marijuana plant in a bath of this solution at least twice per day until the problem subsides.


Diatomaceous earth powder
This method will only work for certain types of marijuana plant pests like gnats and ants, but it is an excellent all-natural solution that is easy to use. Just sprinkle a few teaspoons around the soil of the plant and watch over the next few days as any bugs that cross the protective barrier dry up and perish.

Commercial treatment
For a food safe commercial grade treatment alternative, head over to your nearest greenhouse for knowledgeable advice on which brands, how much and how long they can be used.

Natural predators
For most small insects the very best thing that you can do is take an all-natural route that uses live bug power by introducing a safer alternative like ladybugs who will eat the pests and leave your marijuana plant completely untouched.

4. Droopy leaves

Overturned or droopy leaves are a dangerous sign when it comes to a marijuana plant, but the problem that is causing this symptom might not be so easy to spot without knowing where to look. There are 3 big mistakes that beginners’ growers often make that might lead to this problem, including:

Too much water
If there is water pouring out of the bottom of your marijuana plant pot or over the edges and you are following the advice of using high quality super soil, then you are giving your plant way too much water, and that could be the cause of this unfortunate symptom.

Too little water
This is also a common problem when growers water their plants too infrequently, leading to a nutrient and water deficiency.

Too cold of an environment
No matter what kind of weed plant you think you are growing, all cannabis strains do best in warmer more humid climates, so if you have your plant outside on cold nights, or inside of a house with an air conditioning system set on full blast, then that might be the reason for your droopy marijuana leaf issue.

5. Marijuana leaf burns

If your marijuana plant seems stunted and you’ve noticed a discoloring that is yellow or brown on the leaves, then you are likely facing a burning problem. Luckily, this is one of the easiest on this list to address, as there is a fairly standard checklist to run down to diagnosis this kind of issue.

PH level
Soil PH levels can make or break a marijuana plant crop, which is why it is so important to invest in a home testing kit. That way, regular checks can be done of the safety of the water used and the soil that your plant is in.

Lights placed too close
Another common first time mistake is assuming that more light is always better, and in the case of marijuana grow lights, the majority are strong enough to cause burns on both humans and plants, which is the reason why it is always recommended to maintain a distance of at least 15 cm between your marijuana plant and light fixtures.

Too much fertilizer
If you have recently tried to feed your marijuana plant using any kind of fertilizer including all-natural manures, then you might have caused the burns by applying too much. Fertilizers should never touch a single marijuana leaf and should only be sprayed onto the surrounding soil in minimal amounts. To treat this common symptom, a replanting into fresh soil, or a thorough daily rinsing to rid the growing medium of the toxic chemicals might be necessary.

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