Common mistakes when growing cannabis

Common mistakes when growing cannabis

Common mistakes when growing cannabis


Although growing cannabis is a fairly simple and straightforward process, to grow good cannabis you need to optimize the environmental and other factors in order to produce high yields with high potency and great flavour and aroma.


While optimizing your grow conditions, it’s important to avoid making any major mistakes that new growers often make, that could potentially ruin your harvest or seriously damage or decrease the quality of your harvest.




One of most common mistakes new growers make is wrong light setup or placement. To grow properly, cannabis needs a lot of light and often growers get confused with the output all the different lights have – light spectrums, lumens, watts, PPF, PAR.


The best way to measure the light output is by measuring PAR or Photosynthetic Active Radiation. Various lights emit different color spectrums with different wavelengths and your plants can use some of those while the rest is reflected and PAR is simply the level of available light your plants can absorb and use in photosynthesis. PPFD, or Photosynthetic Photon Flux Density is a way to measure the light intensity or efficiency.


Cannabis seedlings and mother plants will generally thrive in 200-400 PPFD, plants in vegetation will use 400-600 PPFD while plants in flowering can use 600-1000 PPFD or more, if you introduce CO2 to the environment.


Having too weak lights will make your plants lengthy, with much less branching or producing fluffy, not potent buds, while having too strong lights can stun your plants in growth and even burn them if they’re too close. General rule of thumb is to place your lights 10cm for every 100W of the output but that doesn’t apply for the lights of new generation – LED and HID which can be placed (much) lower because they don’t produce so much heat.


If you don’t have a PAR meter, a good method to determine if your lights are placed in a good position is to place your hand on the canopy level, if it gets heated – it’s too close. It’s better to place the light a few centimeters higher just to be safe that the lights won’t damage any new growth too and that you don’t need to adjust the lights again in a day or two. If you notice that your plants have started with longer internodes and are rapidly gaining in height, you might want to put them a few centimeters lower.


PH levels


Wrong PH levels of both the growing medium and your water/nutrients can cause your plants to be stunned or even kill them. Optimal PH for cannabis is slightly acidic, 6-6.5 in soil and 5.6-6.5 in hydro while ideal PH for you water and nutrient should be between 6-7.


Correct PH levels will allow you plants to absorb the full range of nutrients while PH levels that are too low or too high will cause various nutrient deficiencies because the nutrients won’t be made available due to the too acidic or too basic PH, which can also cause nutrient lock up and nutrient build up in your soil. Too low PH levels are toxic to your plant while too high PH will cause slowed or stunted growth.


To check the PH you could use a PH meter, they are available on their own and with EC/PPM meters too and there are models that can measure both liquids and solids PH. When measuring the PH of your water and nutrients be sure to measure it after the nutrients have been mixed because they can change the PH. When growing in hydro, it’s important to measure your PH daily, ideally twice a day, in order to ensure a quick response if needed. Using basic 6.0 PH will allow for an ebb and flow to be between 5.5 and 6.5.


To increase or decrease your PH you can use products as ph-up/ph-down or you can use lemon or lime juice or vinegar to lower the PH and baking soda to raise it. To check your soil based medium PH you can test the PH of the water going in and the PH of water coming out – so called “runoff”. If your runoff is too low – use water and nutrients with slightly higher PH and if they are too high – use water and nutrients with lower PH to ensure the optimal PH of the medium.




Probably the most common mistake growers make is overfeeding your plants. New growers get concerned that their plants aren’t growing fast enough and they think that increasing the nutrients will produce better results. But, there’s a limit of nutrients the plants can use and to measure the levels we use PPM.


Ideal PPM for a seedling or a clone is between 100-250 which is in most cases provided by the soil itself, so no additional feeding is required. As your plants enter the vegetative phase they can intake 300-400 PPM at first and around 700 PPM at the end of vegetation. During flowering, PPM can be increased to 1000 in the first few weeks followed by 1500+ during the second stage of flowering, followed by a flush that should be as close to 0 as possible.


Good soil can have and hold nutrients for at least a couple of weeks but if your plants exhibit symptoms of both excess or deficiency you may want to adjust your feeding accordingly.




Overwatering, along with overfeeding, is probably the most common mistake beginner growers make. While watering with too much water is easily taken care of – by simply draining out, new growers tend to water too often.


Using pots that allow for the excess water to drain out and allow good air circulation is important for the roots not to suffocate and die. Allowing your roots to intake oxygen is as important as giving them nutrients and water. Keeping the roots in stale water and moist medium will cause them to develop root rot and die. When watering make sure that the medium is dry, or at least the few top centimeters. If you’re unsure you can wait for a day more.


Temperature, humidity and airflow


Usually, cold temperatures during the winter months and hot temperatures during the summer months can cause problems in your grow room. Ideal temperatures for growing cannabis are between 20 and 30 degrees Celsius in vegetation and about 2-3 degrees less in flower. High temperatures will cause your plants to drink more water and can cause heat stress while low temperature may cause your plants to slower the growth and use up water more slowly. To correct your temperature you may want to use AC, heaters/coolers or more or better vents and fans.


Humidity plays a key role in the grow environment and optimal humidity should be between 40 and 70 percent. At first, in seedling or clone stage, your plants can use more humidity – between 60 and 70 percent, lowering it to between 40 and 60 percent in the vegetative stage and lowering it even further between 40 and 50 percent in the flowering stage.


Low humidity will force your plants to look for more water from the roots, using up more water faster, so you might need to adjust your watering schedule. Too high humidity will leave your plants more vulnerable to bacteria and various diseases.


Having good airflow is often neglected but having it takes care of a lot of possible issues, including:


  • removing the hot and stale air from the grow area and lowering the temperatures and keeping the humidity in check
  • bugs and pests don’t like and don’t thrive in conditions where there’s a good airflow
  • strengthening your plants by having a gentle breeze blowing on them making them strong and sturdy and capable of supporting big buds


To adjust the air circulation you can simply add more vents and fans or replace the existing ones with stronger ones. With separate vents for intake and outtake of air you should have a fan gently blowing on your plants, just enough to make them dance a bit.


Unreliable and unstable genetics


Although you can always use any and all seeds that may appear in a bud you’re smoking, good and stable genetics are important to ensure a quality harvest. “Bag seeds” can be both male and female and often aren’t mature enough to germinate properly, so if you choose to grow them – keep an eye on their development. Unstable genetics can cause you to have a lot of different phenotypes that will grow in (slightly) different ways and exhibit different growing patterns and shapes.


Ignoring the security


A lot of growers, especially beginners, feel too proud and excited about what they are doing so they like to share that information with everyone. An old growers rule says that for every person that you tell, chances of something bad happening increases by 10%.


Keep your grow to yourself, make sure that there aren’t visible signs of your grow and that no odor is present in and around your grow room. In places where growing cannabis isn’t yet allowed, police poses the biggest threat to your crop but thieves and opportunists can also cause you problems.


Harvesting too early


Many beginner growers are too keen to harvest the buds too early because they can’t wait to harvest and to smoke them. Choosing the right time to harvest is crucial – harvest too early and you’ll end up with less potent and flavor in your buds while harvesting too late can cause degradation processes to start on a number of terpenes and cannabinoids.


The best method to determine when to harvest is to look at the trichomes – little glands that form on the tops of leaves and buds. As your plants mature, the trichomes will start to change their color and go from transparent to cloudy, from cloudy to milky white and then to amber. When trichomes are at milky white they are at peak maturity but not all buds will mature at the same time and not all parts of the bud receive the same amounts of light. Optimal situation to harvest would be when the trichomes are about 15% amber with the rest milky white. Having more amber trichomes will cause more of a couch locked feeling – body stoned while having less amber with cause a more energetic, buzzed type of high.


Why not head on over to The Vault Cannabis Seeds Store and pick up some cannabis seeds now, whilst taking advantage of the discount codes VAULT15 for 15% of your order total and don’t forget to check out our discount cannabis seeds page for all the latest offers, promos and competitions!


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Remember: It’s illegal to germinate cannabis seeds in many countries including the UK. It is our duty to inform you of this important fact and to urge you to obey all of your local laws. The Vault only ever sells or sends out seeds, or seed voucher prizes for souvenir, collection or novelty purposes.

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