10 Mistakes To Avoid when Flowering Cannabis Plants

03 Feb 2023

Flowering Cannabis plants indoors is the most exciting part for a home grower, who has patiently watched their plants grow into a vegetative state, and is now ready to be flowered. It is also during this time, where many things can go wrong, so in this article, we cover 10 mistakes to avoid as a beginner grower when switching your timers to 12/12.

  1. Hot Temperatures

Ideally, Cannabis plants prefer a daytime temperature close to 24 degrees Celsius, with a dip in the lights off temperature to around 18 degrees Celsius. Allowing the temperature of your grow room to exceed 25–30 degrees as a beginner can be problematic, causing a direct correlation with the relative humidity levels and air flow. 

You will also notice the healthy shine and growth structure is now beginning to suffer from heat stress, causing transpiration to also become affected. Over time, the leaves will become dry and brittle and the plants will struggle to uptake nutrients properly, leading to many other nutritional issues.

  1. Distance of Lights

The distance of the grow light to the top of the canopy should remain at a point where the temperatures are cool enough for the plants, and can produce the maximum light spread. If you are using HPS and a reflector, or a modern day LED model, then you will want to make sure the final height of the plants and the distance of the light remain consistent.  

Many growers will initially lower their grow lights, with the intention to increase as the plants grow taller. The best way to know if your light is causing too much heat at the set distance is to place your hand 30 - 45 cm below the light fixture and feel the intensity of the heat provided by the bulbs. 

  1. Poor Air Flow

A good quality grow room will have multiple oscillating fans all turning at different times, set at different heights. The goal is to have a constant fresh current of air blowing around the base of the pots, the middle of the canopy and the space above the tops of the plant and the grow light. 

If you are currently working with one or two small sized fans, then it is a good idea to add another and make sure they are all blowing at different heights 24 hours a day. 

Poor air flow is the biggest culprit when it comes to plant disease like powdery mildew or botrytis entering the garden. Pests like spider mites also prefer a warm, humid and stagnant air environment, so the more air flow you can provide your plants, then the more CO2 can circulate around, and the risk of mold or a heavy mildew infection is significantly reduced. 

  1. High Humidity

Another reason why many growers experience issues with mold and mildew, usually at the same time. Combined with poor air circulation and hot temperatures, then a high humidity level above 40% can have serious consequences, especially when growing a strain known for producing thick, dense and large sized buds. 

During the flowering period, you should aim to lower the relative humidity to as close to 35-40% as possible. Some growers choose to keep a dehumidifier in their grow room to help lower the amount of moisture in the air, allowing them to maintain a consistent environment. 

  1. Lights Off

Depending on where you live, and if you use a heater when the lights are off, can make a huge difference in the temperature the plants experience when in their darkness period. You may have the lights on temperature spot on, however once that heat source is switched off, and with the extraction on 24/7, most can find their lights off temperature is much lower than they would like.

Basically, a large drop in temperature below 15 degrees Celsius can cause the plants stress, and as a result will stretch much higher than normal. A cold and damp grow room will only cause the plant's roots to become cold and may even encourage bad bacteria and pathogens. You should try and keep a 6 degree Celsius gap between lights on and off if possible. 

Over Watering

A mistake that is easily made and, depending on how late into the flowering period you are, can have a negative effect. When a growing medium becomes over saturated, the roots will temporarily become waterlogged and then need time to air out again. 

Not only does over watering your plants slow down how fast they can uptake nutrients and photosynthesize, it can also cause anaerobic bacteria that thrive in a low oxygen environment to infect the roots. The rule of thumb when working with an organic soil medium is to feed 10% of the weight of the pot in liters. So a 10 liter pot only needs 1 liter of water or nutrient solution once the growing medium is drying out. 

  1. No Flush

One of the biggest mistakes beginner growers make is to not flush their plants. This may be down to inexperience and not correctly following a feeding chart, or it could be down to pushing the plants to the limit yield wise. 

Flushing your plants for the last 14 days of 12/12 is an essential process that will produce the smoothest and tastiest flavors possible, as well as pushing your plants to use all their internal nutritional reserves. Not flushing your plants will only cause the final smoking experience to be a harsh and unpleasant one with charcoal black ash.

  1. Harvesting Plants Early

There are signs to look for during the final week of the flowering period, however second guessing and harvesting your plants early is a huge mistake. Unless you have absolutely no choice, then chopping your plants earlier than normal will cause the buds to be lacking in potency and terpenes.

The calyx and bud structure will also be affected, with the end result being a loss of yield as well as plant essence. Harvesting Cannabis plants should be based on the trichome maturity under a microscope lens, how swollen the calyx are and resin production.

  1. Plant Training

Referring to high stress training such as snapping stems / super cropping or a heavy pruning session. It is important to do all your plant training techniques during 18/6, and to avoid any stressful training methods once the plants have started producing buds. 

As a beginner grower, allowing your Cannabis plants to flower and be left alone without any additional tying down, topping, pruning and super cropping will allow the plants to grow stress-free. Too much stress during 12/12 with some strains will induce hermaphroditic traits.

  1. Nutrient Toxicity

The final mistake to avoid is causing nutrient toxicity, which simply means the plants have too much N, P or K and are showing visible signs. One of the worst things that can happen when a plant is exposed to high levels of K, is the leaf structure breaks down and turns soft. 

Combined with a lifeless decomposing smell, it can be hard to pull plants back around from this stage, leaving a beginner or expert grower totally deflated. When it comes to any toxicity when growing Cannabis, the best response is to just feed plain water until the imbalance has been internally leveled out, and the plants are able to grow back as normal 5–7 days later.