Defoliation - how & why it can improve your yields

How & why defoliation improves yields.

Green-fingered people all over the world work hard to grow the best plants and improve the quality and quantity of their yields every single day.

Cannabis growers are always on the lookout for that next tip, trick, tool or technique to elevate their grow and upgrade their skills… Is defoliation it?

Defoliation is a term that’s relevant to gardeners of all types, from hobbyists to commercial growers and it’s a term used to mean several things.

Today, we’ll be specifically looking at how defoliation relates to cannabis or medical marijuana farmers. In particular, those who grow indoors.

In this post I’m going to cover:

• What is defoliation?
• Why defoliate cannabis plants?
• Can defoliation create a better growing environment?
• The function of leaves & the science behind defoliation.
• Leaves regulate transpiration.
• Leaves store nutrients.
• Leaves absorb light & enable photosynthesis.
• So how can defoliation be a positive thing?
• Defoliation prevents microclimates within your grow space.
• What is photorespiration & how to avoid it.
• How defoliation improves grow room efficiency.
• The benefits of defoliation.
• Are there any disadvantages to defoliation?
• When should you defoliate cannabis plants?
• When should defoliation be avoided?
• Top 10 defoliation tips.
• Takeaways.

Disclaimer: Any information given on this site is for educational purposes only. Please ensure if you’re growing cannabis you’re doing so in accordance with the law and subject to appropriate permissions and licenses of the applicable country.

Now that’s out of the way, let’s get to it! 👉

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What is defoliation?

Defoliation is the removal or loss of leaves from a plant, bush, tree or area of land.

Plants can lose leaves through defoliation naturally if exposed to drought, insect pests, grazing animals or disease.

Or defoliation can be a tool used intentionally for agricultural purposes either by using chemical or manual methods.

Defoliation can be detrimental and result in negative or unwanted effects to the plants in question.

Equally, it can be used carefully and intentionally to increase light and air availability, improve vigour or redirect plant resources to a positive effect. 🍃

The cells within a plant that photosynthesise are mainly located in the leaves, so it stands to reason that defoliation done wrong could be bad news!

You definitely need to tread carefully when tinkering with how plants turn light into their energy, which is why there is so much differing opinion about whether defoliation is great or a risky practise.

Note: Defoliation is not the same thing as pruning.

When you intentionally defoliate a plant, you are selectively removing leaves (and only the leaves!)

Pruning (a more aggressive tactic) is selectively removing parts of a plant. Those parts could be branches, nodes, buds or flower sites or roots – this carries more of a risk to your plants.

Why defoliate cannabis plants?

When people talk about defoliation as it relates to cannabis plants, it’s often about maximising yields (because who doesn’t want that right?!) 😉

But often growers unfamiliar with defoliation are (sensibly!) reluctant to start removing bits of their prized plants.

After all, it might seem counterintuitive to start plucking parts off plants that you’re wanting to grow as vigorously as possible.

Growers that are pro defoliation however, know that careful implementation can indeed up the efficiency of their grow whilst improving the quality and quantity of the end product.

The purpose of defoliating cannabis plants is to manipulate their natural processes to encourage heavier cropping in a shorter time through increased energy efficiency.

There are a number of other commercial crops that benefit from and generate higher quality, bigger yields when defoliated including cotton, some palms and cowpeas.

Even though defoliation is a common agricultural practice, there is still much debate about how and when to defoliate for optimal results.

Defoliation when done at the wrong time, or executed too drastically can result in lower yields or stunted growth.

So defoliation is not a magic wand to guarantee increased cannabis yields, it’s a tool in your arsenal, like many others to be thoughtfully chosen and used with caution.

Note: Defoliation is not the same thing as “lollipopping.”

Quite often the terms defoliation and lollipopping are used interchangeably but they’re not the same thing.

Lollipopping does include a focus on defoliating the bottom of the plant to leave stems with more foliage and flower sites towards the top of the plant so that they have a passing resemblance to lollipops. 🍭

But to actually get that lollipop look, lollipopping requires stripping the whole bottom of the plant, removing nodes and sometimes entire branches, not just the foliage (more like pruning.)

Can defoliation create a better growing environment?

We’ve said it before and we’ll say it again… when you grow indoors, managing your environment is everything!

Temperature, humidity, light, water and nutrition are all key.

When cannabis plants grow naturally outdoors, the plants need to ensure their survival.

This involves growing lots of foliage in which the plants can store nutrients for use later in case of any unforeseen shortages of nutrients or water, or in case of attack by pests.

If you grow cannabis indoors though, realistically, all the additional leaves to stockpile resources in case of emergencies actually aren’t needed.

The main benefit of growing indoors is the high level of control you have over your environment, so if you’re providing optimal temperatures and humidities, enough light etc, your plants just don’t need all the extra leaves.

In fact, surplus foliage can become a burden and be a significant draw on resources for the plants.

When you selectively defoliate, you free up energy that the plants would otherwise use to sustain the foliage and channel that energy to where you want it.

By removing selected leaves you also ensure that more of the light available in your grow space can be used by your plants.

Bud sites below a thick canopy get very little light. Flowers that don’t receive adequate light, will stay small and airy.

So it makes sense that if you defoliate to allow light to penetrate, exposing the buds, you can increase your yields.

Defoliation also improves airflow around your plants which promotes more CO2 absorption.

Airflow helps regulate temperature and humidity, this means there’ll be less chance of hot or humid areas or microclimates within your grow space which if left unchecked increase the risks of pests and mould.

Can defoliation create a better grow room environment? – Yes, yes it can!

The function of leaves & the science behind defoliation.

Right, it’s time to dive a little deeper into the purpose and function of leaves and the science behind defoliation. 🤿

Leaves regulate transpiration.

Transpiration is the process of water moving up through a plant and then evaporating through stomatal openings on the leaves and stems.

Water is obviously essential to healthy plants, but in fact only a very small percentage (0.5% – 3%) of the water taken up by the roots is actually metabolised into sugars and used for growth.

Most of the water taken up (97% – 99.5%) is lost to the air via transpiration.

Why do plants transpire?

Plants transpire to take up nutrients along with water from their roots.

But what this means is that the leaves function here is to facilitate evaporation of surplus water into the surrounding air. Larger and more leaves enable faster transpiration and water loss.

Leaves store nutrients.

Another function leaves perform is to store the aforementioned nutrients that they’ve taken up with water via transpiration. To a lesser extent, the stems of your plants store nutrients too.

When your plant’s leaves are a lush deep green, that represents health. 🌿

If you begin to see changes in the colour or texture of your leaves, this can indicate a deficiency.

The changes you see are a symptom of there not being enough of a specific nutrient in storage within the leaves.

Often, the discolouration that you see due to deficiency is down to the plant drawing a specific nutrient away from a leaf because it is needed more elsewhere in the plant – in growth of new shoots for example.

This highlights that it is always essential to have enough leaves to minimise the risks of your plant suffering nutrient deficiencies that can impact health and vigour and the quantity and quality of your yields.

Leaves absorb light & enable photosynthesis.

The primary function of leaves is to absorb light and use it to turn carbon dioxide (CO2) and water into sugars to fuel the plant and oxygen (as a byproduct) via photosynthesis.

It’s helpful to think of leaves as solar panels – the more light they’re exposed to, the more energy they can provide for the plant to use.

But what that means is that all those leaves in shade, covered by other leaves and shielded from the light above are not able to photosynthesise and contribute to the plant in a meaningful way.

Now that we’ve covered the function of leaves, let’s take a look at how defoliation can help to create the ideal environment for indoor plants to function at peak efficiency.

So how can defoliation be a positive thing?

Selectively removing leaves can ensure that your plants have access to the optimal amount of light and CO2.

To find out more about the importance of CO2, visit this post about supplementation and temperatures and CO2.

Careful defoliation can also promote the best conditions for transpiration by making it easier for you to provide your plants with optimal, stable, temperatures, humidities and vapour pressure deficit (VPD.)

These things can work together and really boost photosynthesis.

But there’s an even greater benefit…

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Defoliation prevents microclimates within your grow space.

Microclimates in your grow space, are small areas or pockets of air in which the environmental conditions are different from what you’ve chosen to provide for your plants.

Sometimes the difference is only slight, but sometimes the difference can be substantial.

As an example, if you’ve deduced that the optimum temperature and humidity to be running your grow room at are 26°C (79°F) and 55%…

Then you take measurements amongst your canopy using a grow room sensor or thermometer and hygrometer. 🌡️

You’ll likely find that those figures are different (likely cooler & more humid.) This is a microclimate.

You’re most likely to find microclimates in the centre and underneath your canopy and at the edges of your grow room.

This is because these areas are often shady and have less air flow… Uh oh! Alarm bells should be ringing! (Checkout the section in this post about dispersing the boundary layer for more info!)

Shady, humid, stagnant pockets of air provide ideal conditions in which pests, mould and mildew can thrive.

This is the reason that it’s so important that you consistently monitor your grow environment and respond accordingly.

This kind of environment also impedes photosynthesis as lack of airflow means there’ll be a lack of CO2 available. This causes an undesirable process called photorespiration to happen.

What is photorespiration & how to avoid it.

Photorespiration is a naturally occurring process in plant metabolism, but one you definitely want to avoid where possible!

Photorespiration can occur as a result of drought or water stress, but in this example, photorespiration happens as a result of microclimates creating a stagnant moist environment in your grow space.

Transpiration rates slow down because when the air in the space around the leaves of your plants becomes too humid and saturated, water vapour can’t evaporate from the stomata.

This is because of the low vapour pressure deficit. Low VPD is when there is not enough difference in pressure inside and outside of the leaf to encourage normal transpiration.

When your plants experience these conditions they can’t respire efficiently.

Low CO2 levels in the surrounding air (due to your plants previously using it all up) and poor circulation not replenishing it cause photorespiration to happen.

In normal photosynthesis your plants use light to take in carbon dioxide and release oxygen.

But during photorespiration, your plants use light to metabolise oxygen and release carbon dioxide.

This reversal of the normal process results in your plants consuming sugars, not producing them and carbon and nitrogen is lost which slows down plant growth.

Photorespiration wastes energy and reduces the efficiency of photosynthesis – not good!

How defoliation improves grow room efficiency:

Leaves serve several important purposes:

• They regulate transpiration,
• Store nutrients,
• Absorb light and facilitate photosynthesis.

But surplus foliage inside a confined grow space presents problems:

• It creates undesirable microclimates.
• Shade and stagnant, humid air makes CO2 unavailable for your plants to use.
• This forces your plants out of photosynthesis and into photorespiration.
• Which wastes energy and will slow down growth.
• Resulting in smaller, less vigorous plants susceptible to pests.
• Directly affecting the quantity and size of buds and end product.

This tells us that in order to maximise efficiency in your grow space, you need to remove leaves that contribute to these undesirable efficiency zapping microclimates.

Whilst leaving some leaves to photosynthesise and store nutrients.

The benefits of defoliation.

By now, you’ll know there’s a number of plus points to defoliation, but lets touch on the benefits one more time:

• Maximises light penetration and therefore absorption by enabling light to get to all parts of the plant.

• Increases air flow and in turn CO2 absorption which in conjunction with increased light can increase photosynthesis.

• Improved airflow minimises the risk of pests and parasites alongside helping prevent mould and mildew

• Selectively removing surplus leaves frees up energy to be better used elsewhere.

• Defoliation done right promotes higher quality and yields resulting in a better end product.

Are there any disadvantages to defoliation?

Yes… but any downsides are more often than not a result of grower error and overzealous defoliation done wrong that in turn causes problems.

Defoliation done badly or at the wrong time in a plants life cycle can:

• Damage plants resulting in slow or stunted growth.

• Which then leads to poorer quality and diminished yields.

As is the case with many tools that growers have at their disposal, defoliation could be your next powerful secret weapon… or your worst enemy!

So be sure to thoroughly research and understand defoliation before getting scissor happy! ✂️

When should you defoliate cannabis plants?

Well, this topic is a blog post or two (more more!) in its own right!

Some growers defoliate in vegetative growth, some defoliate during the flowering stage.

Growers sometimes defoliate multiple times during the vegetative stage, or flowering, or both!

When, and how much you should defoliate your plants will be very much dependent on your own unique indoor set up and what types of plants you are growing.

We’re creating more content on this extensive topic so – watch this space!

Although knowing when to defoliate for the most impact on quality and yields can be difficult, there are times when you should definitely defoliate proactively. These are:

1. Pests and diseases.

If you notice that your plants are showing signs of pest problems such as spider mites, or diseases such as powdery mildew, you should remove all affected leaves and dispose of them safely – immediately.

Checkout this post on spider mites & how to manage them for other top tips to use in conjunction with selective defoliation.

2. Discoloured or burnt leaves.

If some of your plant’s leaves are yellow or brown, that shows they’ve given up all of their stored nutrients to be used elsewhere, this could indicate the plant has nutrient deficiencies.

In this case, removing healthy green leaves might not be such a good idea but definitely remove brown or yellow leaves immediately to prevent them attracting pests or inviting disease.

When should defoliation be avoided?

When not to defoliate is a topic almost as hotly debated as when to defoliate!

Some growers never defoliate in vegetative growth, some wouldn’t dream of not defoliating during veg, some say never defoliate multiple times, others are more than happy to.

It also depends on what type of cannabis you’re growing, you’ll find growers who are happy to defoliate autoflowers and those that absolutely wouldn’t.

Although knowing when not to defoliate for the most impact on quality and yields can be difficult, there are times when you should definitely stay away from defoliation. These are:

1. Small seedlings or clones.

Seedlings and clones are delicate and fragile, let them grow without adding extra stress through unnecessary defoliation. 🌱

2. Plants growing outdoors.

As previously mentioned, cannabis plants grown outdoors actually do need their leaves as a nutrient store in case of emergencies or stress.

Also, whereas a light in your grow room stays static, the sun’s position in the sky moves throughout the day.

That coupled with the fact that the sun is (much!) more powerful than your grow lights means that the sun’s rays will be able to penetrate better and reach more leaves which means that they don’t need or benefit from defoliation in the same way.

3. Visibly sickly looking plants.

This should be obvious but just in case… don’t remove healthy leaves from plants that otherwise look frail, sickly or like they’re suffering from any kind of deficiency or pest problem.

The process of removing leaves that are healthy in this situation is going to really impede your plants ability to fight off any issues it’s facing and bounce back stronger!

Top 10 defoliation tips.

1. Always use clean, sharp scissors to minimise risks of infection or disease and go slowly! If you’re new to defoliation, aim to take no more than 10-15% of your plant’s surplus foliage at any one time.

2. Don’t tune out! It’s all too easy to get into a rhythm of removing leaves when you’re defoliating a plant, stay present and don’t get carried away.

3. Start at the bottom of the plant. Foliage at the bottom of the plant is usually fairly safe to remove.

4. You can’t put leaves back! Always take off less than you think, especially if you’re not experienced with defoliation. You can always take more leaves away later.

5. Swat up on strain specific defoliation. Different cannabis strains respond to defoliation differently. Bushy indicas tend to be good candidates, whereas less densely foliated sativas naturally have less leaves to spare.

6. Don’t try to defoliate plants that are not in peak condition, you’ll only stress them out.

7. Practise makes perfect. There is a fine line to tread to make sure you don’t tip the defoliation vs transpiration needs of the plant balance.

8. Use a grow room sensor to continually monitor your grow space’s temperature, humidity and VPD etc 24/7. This will give you invaluable insight into your plants’ health and how defoliation influences your environment.

9. Getting a bit scissor happy can result in overfertilisation and nutrient stress. This can show through burned leaves or nutrient lock out. You may need to vary your nutrient strength or feeding schedule accordingly.

10. Be mindful if you’re not using salt based nutrients. If you’re using organic soil that you’re not feeding, you don’t want or need to take away the leaves storing the plant’s nutrients!

Takeaways:

Defoliation is the removal of surplus leaves from your cannabis plants. It’s a technique that if used correctly can maximise quality and quantity of yields.

The leaves of your plants play a crucial role in ensuring the best quality and largest quantity harvest possible.

Even so, from an environmental perspective, the microclimates that surplus foliage creates can be severely detrimental.

You can verify this by using a grow room sensor or thermometers and hygrometers at different places within your grow space to learn about your temperature, humidity and microclimates.

There are numerous benefits to defoliation. Ensuring maximum light penetration, increased airflow and CO2 availability, reduced risks of parasites and disease and freeing up energy to be used elsewhere.

There are some downsides too, but these are usually down to grower error. Defoliation at the wrong time or done badly can damage your plants and stunt growth and yields.

When during the growth cycle to defoliate is a hotly debated topic and a post for another day.

But there are definitely times you should not defoliate – if you’re growing outdoors, if your plants are seedlings or young clones or if your plants are visibly not in perfect health.

Defoliation is not something to be frightened of, but not something to jump into blindly either because it’s sometimes considered a high stress training technique.

If you’ve never defoliated a plant previously and you decide to give it a go, it’s a good idea to research other lower stress plant training techniques that you can try first to ensure better airflow, light and CO2 availability for your plants.

… But if you’ve tried all that and you’ve read up thoroughly, start low, go slow and you’ll do fine! 😄

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