Everything taught and sold by BudTrainer is to be used strictly for legal purposes. We absolutely condemn the production of illegal substances, and it is your duty to ensure that you are complying with the law. The words "hemp", "cannabis", "weed", and "marijuana" are used interchangeably to refer to the same plant (legal hemp with less than 0.3% THC) for the purposes of this lesson.
How to Defoliate and Prune Your Plants for Maximum Yield
Updated on Aug 04, 2022
" Simple! Defoliation & pruning have some key benefits."
1. It increases overall yield
2. It increases cannabinoids
3. It produces bigger buds
4. It decreases pest pressure
Did you know that...
Nearly 100% of legal commercial cannabis growers defoliate and prune their cannabis plants? If they didn’t, they would run into multiple problems such as pest pressure and low-quality bud.
No more waiting. Let’s get right into it!
But before we get there, do you have everything you need?
Defoliation & Pruning
- Garden scissors (optional)
- Rubber gloves (optional)
First off, what is the difference between defoliating and pruning?
The act of removing or cutting the leaves off a plant. “Folia” = leaves in latin.
The act of removing or cutting the branches off a plant.
Defoliating = cutting leaves || Pruning = cutting branches
Do NOT defoliate or prune when:
- Before the 5th node appears: young seedlings are fragile and they need as much nurture and care as possible. This is why it is important to leave your cannabis seedlings untouched until they have at least 5 nodes.
- 3 to 5 days before flowering: always leave 3 to 5 days between defoliating/pruning and switching your plant to flower. This way it has a few days to recover from the stress caused by cutting its parts.
- Between day 1 and 21 of flower: during the first 3 weeks of flower your marijuana plant is going through an aggressive growth period (called the stretch phase), and any defoliation or pruning during this phase stunts its growth severely.
Vegetative Stage Defoliation & Pruning
When: after your plant has a total of 5 or 6 nodes
Topping is probably the most popular pruning technique available. It involves cutting your main branch right after a node (pair of leaves + growth sites), so that the remaining growth sites can turn into stronger branches. This allows cannabis plants to “bush out”, since topping breaks the tendency of the plant to grow into a Christmas tree shape. Topping is highly recommended, and if you haven't yet you can learn how to top in this article.
Cannabis seedling that was recently topped
When: after 4 to 8 weeks from planting your seed
At this point, many leaves and small branches will have appeared, inhibiting your plant's ability to absorb CO2 and light in the center of the canopy. This is why it is important to defoliate and prune the middle of your canopy at this point, giving your plant the structure it needs to continue growing. On top of this, it is also important to start training your marijuana plant at this stage, if you haven't yet.
Cannabis plant with many shaded leaves, ready for defoliation
Before and after defoliation on a vegetative cannabis plant
You can then continue defoliating and pruning your plants every 2 weeks after that, up to 5 days before flipping to flower (it is important to give your plants at least 5 days to recover from the stress before you flip them to flower). If you are growing outdoors, you can continue defoliating and pruning until about the middle of July, at which point most plants will start automatically switching to flower.
"Cannabis plants only have two types of leaves…"
Fan Leaves vs Sugar Leaves
Fan leaves (7-fingered leaves) vs sugar leaves (single-tip leaves)
When: after 4 to 8 weeks from planting your seed
Pruning and defoliation often go hand in hand. It is much better to prune at the same time as you are defoliating because they are both stressful activities for the plant.
Prune the smaller shoot to allow its larger pair to grow stronger
Prune shaded branches to allow larger ones to grow stronger
Learn to Grow Like The Pros
Flowering Stage Defoliation & Pruning
Most strains will go through a vigorous growth period between the time you flip them to flower and the 3rd week of flowering. While it is really important NOT to defoliate your plants during these 20-25 days of the stretch phase, it is equally as important to trim them back after this period is over. This is the last chance you have to prune any unwanted growth or leaves before your plant starts filling up with flowers.
NOTE: NEVER top your cannabis plants during the flowering stage, as this will only stunt your flower production.
Weed plant after the 3rd week of flower ready for defol
First, defoliate all bottom leaves and growth sites that aren’t catching any more light and that are blocking the airflow from the bottom to the top (first video). This is important because if you leave too much of a cluster behind, you will end up with a lot of larfy popcorn bud after harvest. Then, make sure to defoliate the leaves at the top that are blocking the lower bud sites from light exposure - this ensures they develop into dense colas in the future (second video)
Defoliating and pruning after the 3rd week of flower
Defoliating a cannabis plant to expose the shaded tops
A great technique that can be used at this stage is called “Cannabis lollipopping”, where you defoliate the bottom half of your plant, leaving only about 8” to 12” of canopy at the top. Lollipopping is great after the 3rd week of flower, as it helps clear out small growth sites that would otherwise become popcorn bud.
In order to accomplish a lollipop, just choose the height you want to lollipop at (8” to 12” from the top), and then defoliate all leaves and growth sites below that line. Lollipopping is highly recommended indoors, where the light intensity is significantly lower the farther away your leaves are from the light source.
Lollipopping: the shaded leaves and branches were pruned
1 week before harvest time, your cannabis plant will have put on most of its weight and will start focussing on filling up its trichomes with cannabinoids. This is when most of your pistils are brown and the trichomes are going milky and amber. It is recommended for you to do one last defoliation (no pruning) at this stage for a few reasons.
1. It helps uncover those lower buds and sugar leaves that have been shaded by a big fan leaf for the last 4 to 6 weeks.
2. It causes a mild stress on your plant and forces it to allocate all of its resources to the buds, which results in more trichome and cannabinoid production.
3. It saves you over 50% of the time trimming because most of your fan leaves will have been already removed.
Weed plant 1 week away from harvest and ready for defoliation
Cannabis plants after pre-harvest defoliation
Cannabis bud after pre-harvest defoliation
Want to train your plants like the ones in this article?
" Easy peasy! You can use pruners (recommended) or just your fingers."
How to defoliate & prune with scissors
Using the Slide'N'Snip technique on cannabis leaves
How to defoliate & prune by hand
Pinch the leaf or branch by the base and you can more easily break it off
Learn to Grow Like The Pros
But wait... I still have some questions!
" Hint: it all comes down to light exposure and airflow "
Defoliating & Pruning Indoors vs Outdoors
Our sun is nearly 100 million miles away, which means that it doesn’t matter if your plant is a few ft taller or shorter - the bottom and the top leaves will feel no difference in light intensity (as long as they are not in the shade). However, when it comes to indoor lighting, the intensity of your grow light decreases a lot as you get farther away from the source - from 5 to 10 times weaker every foot of distance away.
What this means is that training cannabis indoors is more about optimizing light distribution at the top, such as maintaining a flat canopy and defoliating the bottom of the plant (like the plant on this diagram). When growing outdoors, however, you don’t need to worry so much about this - just make sure to choose a spot in your backyard that has the most amount of sunlight, all day long, and you can have leaves from top to bottom (just not in the middle!).
Airflow is essential for plants to absorb CO2 as it helps circulate the air released by the leaves (which is full of oxygen) and renew it by air that is full of CO2. For this reason, it is equally important to train indoor and outdoor marijuana plants to maximize airflow around the leaves and inside of the canopy.
The main difference, however, is that outdoors plants have the extra pressure from pests while indoor plants generally don’t. This is why we highly recommend defoliating outdoor plants at least once a month to clear out all old leaves that are turning yellow, not catching any more light, or that are blocking airflow to the middle of the plant. As long as you don’t create pockets of clustered leaves, you should be safe from the pressure of pests!
In a damp backyard like this, defoliation helps keep the pests away
" The answer is simple: you don’t! "
Defoliating & Pruning Autoflowers
Autoflowers only have around 30 days in the veg stage before they automatically go into the flowering stage (AKA “auto-flower”), so it is best to avoid defoliating as much as possible, and only cut yellow or brown leaves, or bud sites that are really small and in the middle of the canopy.
It is also not recommended to defoliate more than 10% of your autoflowers’ leaves at once, and definitely not recommended to top them, otherwise the stress can be too much and the growth will be stunted.
The only time when it is recommended to defoliate your autoflower cannabis plants is 1 week before harvest (the pre-harvest defoliation mentioned above). This allows you to avoid too much trimming after you harvest, and forces all of those trichomes and cannabinoids to come out due to the added stress at the end of the cycle.
On autoflowers, only remove sick leaves and small shoots
However, it is not all doom and gloom for autoflowering marijuana plants. Autoflowers are the best candidates for low stress training, which is the most popular training technique and helps increase your airflow and light exposure the same way. Here is a full article on how to low stress train your cannabis plants.
"Fair enough! How about some good old science to explain it all?"
The Science of Cannabis Defoliation
Why does defoliation & actually increase your yields?
It all boils down to 3 vital leaf functions and a common enemy they are fighting.
The 3 Key Functions of Cannabis Leaves
1. Light Absorption
One of the main purposes leaves serve is that of catching light and using it to convert water and CO2 into oxygen and sugars through photosynthesis. In this context, then, leaves serve primarily as solar panels and the more exposure to light they have the more photosynthesis they will be able to contribute to the plant. Conversely, if leaves are completely covered or shaded, they will not be able to photosynthesize. It would be the same as putting one solar panel on top of another - the bottom panel won’t catch light.
This is why it is important to prune leaves and branches that are shaded by 2 or more other leaves on top of them, or that are touching one another.
Transpiration is the process by which water vapor and oxygen (for us to breathe) leave the plant through the stomata - these tiny little openings under the leaves - while CO2 comes in from the air, thus allowing the photosynthesis process to happen. In fact, 95-99% of all the water that plants consume through the roots go back out into the air through the leaves while only 1%-5% stays in the plant and gets converted into sugars. This means that if your plant consumes 1L of water per day, it is "vaporizing" around 950-990 ml back into the air.
So why do plants waste so much water? Well, it's not really a waste. Something else that happens while all of this water comes up from the roots is that the stems, leaves, and flowers take up all of the nutrients in it. So via transpiration, plants are pulling water from the ground, filtering out the nutrients and a little bit of that water for photosynthesis, and evaporating the rest of the water into the air (while taking up CO2).
This is why it is so important to prune everything that is blocking airflow within your plant, otherwise the humid air can never be carried away and exchanged for dry air full of CO2 again.
3. Nutrient storage
Another purpose that leaves serve is storing the nutrients they just absorbed from the water, so that they can use them later. Nutrients like N, P, K, and Mg are mobile, meaning that your plant can remobilize them from the old leaves to the new ones if they are suffering deficiencies.
For example, when the leaves at the bottom of your plant start to go yellow, they are simply "donating" their stored Nitrogen to the new leaves, shoots, and flowers at the top.
That’s why having a certain amount of green and healthy leaves is always important - it helps your plant remobilize those stored nutrients to its most vital parts. If you strip your plant naked like some folks do, you leave no buffer for it to mitigate nutrient deficiencies.
The Enemy: Microclimates & Photorespiration
Avoid these and you will be set
Microclimates are little pockets of air in different parts of your growing space that are different from the overall climate you set. For example, you can set a temperature of 26C/79F and RH55% in your fancy exhaust fan, but if you measure the middle of your canopy you will end up with a cooler temperature and higher RH.
Microclimates are most common on the corners of your growing space, the underside of your canopy, and in the middle of the canopy where it’s humid. Since these areas are usually more shaded and have less airflow, they make the perfect environment for pests to thrive in and the worst environment for photosynthesis to happen - this is why it is so important to defoliate clusters of leaves in the middle of your canopy and avoid microclimates.
Plants don’t just absorb CO2 during photosynthesis, they also absorb oxygen “by mistake” in a process called photorespiration - where instead of producing sugars, they consume sugars - becoming smaller instead of bigger.
Have you ever noticed how small and light-green the leaves inside your canopy are? That’s because there is too little CO2 and so the leaves are respiring more than transpiring, i.e. consuming more than producing.
In other words, when you have a microclimate your leaves are consuming all of the CO2 available around them until there is no more, at which point they are forced to increase photorespiration and decrease photosynthesis.
To summarize: shade + stale air = less CO2 + less light = more photorespiration + less photosynthesis = smaller plants/leaves/bud sites + more pests
Leaves are useful for 1. Light absorption, 2. Transpiration, and 3. Nutrient storage.
In order to make your leaves work hard you need to avoid microclimates because they stunt growth and attract pests.
The more light penetration and airflow you can get in the middle of your canopy, the better your results will be.
Don't be afraid!
It is very common for new growers to fear defoliating and pruning their cannabis plants. After all, you are hurting them by cutting it up. But if you start slow and follow the rules you just learned, you will always have great results!