Improving Cannabis Growth: A Guide to Perlite for Cannabis Soil

You’ve been using your soil for a bit, but as it turns out, your soil has gotten more compact over time. It holds too much water and your roots have started to suffocate. 

What can you do to fix this issue?

Don’t sweat it just yet. There’s an easy way to quickly improve your soil’s drainage and aeration, and it’s called perlite. By simply adding this compound to your soil, you can solve the issue quickly. But how do you use it?

In this article, learn everything you need to know about perlite, including its pros and cons, and how to use it for the best cannabis growth. 

What is Perlite? 

Perlite is an interesting compound that gets added to soil for various reasons, but let’s first understand what exactly it is and how it is made. Essentially, this compound starts as an obsidian — it occurs naturally in the world as lava cools quickly and turns into volcanic glass. 

When this obsidian/volcanic rock is hydrated through a process, the water turns it into perlite. However, the one you’ll find at your local horticultural store looks a lot different from the perlite that exists in the world. 

This is because store-bought perlite goes through one more process before it’s sold to you. The manufacturers essentially crush and heat the perlite to 1796°F, which not only makes it expand 20 times its original size but also turn soft. This expanded perlite is white, has a porous texture, and almost looks like popcorn.

So, why is this volcanic popcorn added to cannabis soil by growers? It has various benefits; it's sterile, lightweight, and lasts a long, long time. Plus, perlite is completely neutral in terms of its pH, so it doesn’t affect the soil’s pH either. 

The most important point why you should add perlite to your soil is because it is very porous and improves your soil’s water absorption and retention abilities — it’s essentially a porous, expanded piece of glass. 

Pros and Cons of Perlite for Growing Cannabis

We hinted at the pros of perlite above, but let’s dive further into them and look at its advantages. At the same time, let’s also check out some disadvantages of perlite that you should be aware of before bringing this compound into your garden and soil. 

Pros of Using Perlite for Growing Cannabis 

So, how does adding this volcanic glass to your cannabis soil improve its growth and yield? Here are some of the ways perlite helps the cannabis plant’s soil.

• Improved Drainage 

When growing cannabis, you need to ensure your cannabis plant has adequate drainage. Otherwise, you’re asking for trouble. If the soil holds too much nutrients and water without letting the excess out, it can lead to problems like anaerobic bacteria, fungal diseases, damping off, root rot, and much more. 

By adding perlite, you can increase your soil’s draining ability so the water does not pool up. This can reduce the chances of your cannabis plant suffering from issues like root rot or stagnation, which can be nasty problems to deal with. 

• Improved Aeration 

Similarly, your cannabis plant’s roots need to breathe. This is because apart from absorbing nutrients and water, plant roots also exchange gas. If the soil is too compact or lacks air pockets, the roots can suffocate. 

So, adding perlite can improve the aeration of the soil, preventing the roots from suffocating. This will further make sure the roots develop well and can absorb nutrients properly, leading to healthy plant growth. 

• Reduced Soil Compaction 

Similar to the issues mentioned before, soil can get compact over time. Tightly packed soil is never good for cannabis plants; instead, it needs to be somewhat fluffy to ensure good growth. 

If the soil is compacted, it loses its drainage and aeration while also eliminating air and water pockets from within. By adding perlite, you can bring some level of fluffiness to the soil so it does not end up doing more harm than good. 

• pH Neutral

Lastly, perlite has a neutral pH, so you don’t have to worry about it affecting the soil’s pH over time. This makes it very easy to use in soil since you don’t have to worry about nutrient toxicity or lockouts while using it. 

Cons of Using Perlite in Cannabis Soil 

Alas, not all that glitters is gold, and this applies to perlite, too. It comes with a few downsides that you must be aware of before you add it to your soil, such as the following.

• It’s Irritating and Dusty

Perlite, as strong as it may appear to be, is kind of fragile and often breaks when handled roughly. So, during transport or regular handling, it can break into tiny, sharp pieces that can be irritating to deal with. 

Plus, it is very light, so the tiny pieces can fly with the wind and end up in your eyes or nose. This is why it is recommended that you wear safety glasses and a mask when handling it on a windy day. 

• Not Always Eco-Friendly 

While perlite exists in nature and is safe for the environment, the manufacturing process itself isn’t always eco-friendly. More on this later. 

How to Add Perlite to Soil for Growing Cannabis

Now that you know the benefits and downsides of perlite for growing cannabis plants, it’s time to put it to use. If you want to bring the benefits of perlite to your cannabis garden, it is best to use it as a soil amendment, not a growing medium in itself. 

First things first, you need to weigh your soil before you add any perlite to it. How much perlite you use depends entirely on you and what kind of soil you have. If your soil is heavy or too compact, you may want to add more perlite than otherwise. 

Generally, when it comes to cannabis gardens, you have two options. 

If you simply want to aerate your soil and improve its drainage without losing its water retention abilities, you should only add 10% to 20% to the soil. 

On the other hand, if you want to significantly ramp up drainage, you can add 30% to 50% to the soil. Yes, this will lead to your soil draining a lot quicker, so you need to be on your toes with the nutrient inputs. 

Can You Add Perlite to Coco Coir for Growing Cannabis?

What if you are using coco coir instead of soil? Can you still reap the benefits of perlite as an amendment? Yes, you can! Perlite works well with other growing mediums, too, especially coco coir. If you plan to add perlite to coco coir, make it 30% for the best results in terms of improved drainage and aeration. 

Can You Use Perlite on its Own for Growing Cannabis?

So, can you grow marijuana using 100% perlite? Well, it depends…

While growing your cannabis plants solely in perlite is possible, it comes with several challenges that need to be addressed if you have no other growing medium. Perlite can serve as an excellent growing medium when used in hydroponic setups with net pots. In this system, perlite allows young roots to penetrate through to the nutrient reservoir below, providing aeration and support throughout the growing cycle.

Sure, perlite offers way too many advantages from aeration to drainage, but it lacks the nutrients needed for sustaining marijuana plants throughout their growth cycle. Plus, it lacks critical components like microorganisms and water-holding capacity crucial for optimal cannabis growth.

Still, if you want to go for it, here are a few things to consider to grow cannabis in just perlite:

Nutrient Availability 

Perlite is inert in nature, which means it doesn't contain the nutrients for plant growth. Cannabis, like most other plants, requires a balanced mix of both macronutrients and micronutrients for it to thrive. This means that it not only needs nitrogen, potassium, and phosphorus but also other elements like magnesium and calcium to name a few. 

Growers provide all these nutrients through a growing medium like soil or supply it through fertilizers. So, if you want to grow cannabis in just perlite, you should provide every nutrient or the plants won't survive. You can do this by making your own hydroponic solution. There are tons of such nutrients available but choose high-quality ones so the pH doesn't fluctuate too much. 

Watering and Irrigation

Due to its porosity and excellent drainage properties, perlite doesn't retain any moisture. You can get around the nutrient problem by providing nutrients to the plants in a precise manner, but this problem is slightly challenging to fix. 

Cannabis plants will grow only if the growing medium is moist. This means that it can't be too wet or dry. For example, if you overwater the plants, it can lead to root rot. In addition, you'll have to fight against many other problems that occur due to the soil being moist, with mold being one of them. 

On the other hand, underwatering the plants will also cause problems. The plants get dehydrated and won't be able to grow properly. Growers who don't want the risk of both these problems use drip systems that help maintain the right moisture levels. 

If you're growing cannabis only in perlite, you need to supply water in such a way that the plants don't suffer from drought or overwatering issues. While this is easy to do in growing mediums like coco coir or soil, it's challenging in perlite, so you'll need to use automated watering systems to avoid underwatering the plants. 

pH

Cannabis plants are very sensitive to fluctuations in pH levels, and this is especially true if you're growing them only in perlite. Therefore, make sure you regularly test and adjust the pH levels of both the nutrient solutions and run-off water to avoid lockout or toxicity. The optimal pH range for absorption should ideally be between 5.5 and 6.5 as you're growing in a soilless medium. 

Stability 

Although perlite provides aeration for root growth, it may not offer stability for larger cannabis plants. Supporting the plants with stakes or trellises can help prevent them from falling over as they mature.

Temperature 

Perlite's poor heat retention properties can cause fluctuations in root temperatures, especially if you live in a cold climate or growing indoors. So, you may have to check the temperatures constantly to ensure they are in the right range. Just to be clear, we aren't talking about the room temperature. Instead, you should focus on the temperature of the root zone. If you notice the plants showing signs of trouble, you may have to insulate the root zone to keep it warm and stable. 

Pests and Diseases

When using 100% perlite, there is a risk of pests and diseases affecting cannabis plants. To prevent this, you can sterilize your perlite, especially if you've used it before to grow plants. Also, keep your grow room clean to prevent infestations and diseases.

In short, growing cannabis in 100% perlite is technically feasible. But you will need to be vigilant and manage everything from the nutrients, pH, and irrigation precisely to make sure the plants don't suffer. 

Due to all that effort, it's not recommended that you grow cannabis in just perlite. Like other growers, you can incorporate perlite into a soilless blend or hydroponic setup rather than using it as the sole growing medium to create a more stable and nutrient-rich setting for cannabis plants.

Is Perlite Safe and Eco-Friendly?

This is a tough question to answer because perlite can be eco-friendly and organic depending on how you look at it. For example, from a chemistry point of view, perlite lacks carbon completely, so it is technically inorganic in nature. 

On the other hand, from the perspective of a cannabis grower, perlite does not contain any unnatural or harmful materials — it’s completely safe for the environment. Heck, it naturally occurs in the environment, just in a different form. So, if you are wondering whether you should use perlite in your cannabis soil, don’t worry about it harming the environment. 

Do note that, sometimes, the manufacturing process for perlite may not be the most eco-friendly. So pay attention to where your perlite comes from. For example, to extract perlite, huge mining operations take place that extract this glass from the ground. 

And let’s not forget the long internal shipping logistics that go into bringing this from the factory to your doorstep. It’s also a non-renewable resource and sometimes irritating. 

Can Sand be Used Instead of Perlite for Growing Cannabis?

Although both sand and perlite serve as soil additives to enhance drainage and aeration, they possess different characteristics. However, you can use them both to grow cannabis, depending on what you're aiming for. Let's compare both to determine if sand can serve as a substitute for perlite:

• Aeration

Perlite: With its porous nature, perlite excels at providing drainage and aeration when you combine it with soil or other various growing mediums. Its high porosity enables moisture retention while preventing water-logging, and fostering solid root development.

Sand: Sand is also good at draining excess water. However, it's not as good as perlite when it comes to aeration. Aeration is very important when growing cannabis as oxygen helps the roots develop very well. This is why growers choose containers with great care. A good container helps with aeration whereas a regular container like plastic may not offer the aeration the plants need. Aeration also prevents the roots from getting root-bound to a great extent. Sand is dense in nature, unlike perlite's light composition. It also gets compact with time, ultimately hindering the growth of the roots. 

Another con of using sand is that while it drains water, it also retains too much water. This may sound contradictory but you can test it yourself by pouring some water on sand. Not only does it take an inordinate amount of time to dry, but it also gets very heavy. So, if you water just a bit more, it can lead to overwatering and harm the roots. 

On the other hand, perlite dries fairly quickly and doesn't get overly dense. 

• Nutrient Retention

Perlite: Perlite doesn't contain nutrients and is mainly used to improve soil structure and retain moisture.

Sand: Similar to perlite, sand doesn't offer nutrients to plants. However, it has the capacity to hold some nutrients compared to perlite. While this is an advantage, sand also gets compacted with time, as mentioned above, and this can lead to deficiencies if you don't notice it and act on time. 

• Root Development

Perlite: The lightweight and porous nature of perlite is beneficial for root growth as it allows roots to access oxygen and nutrients easily. It also helps the roots to branch out easily. Most importantly, it can prevent root rot due to its excellent draining ability. 

Sand: While sand can support root systems to some extent, it may not provide the level of aeration and drainage as perlite, which is very important for root development. If you mix sand with soil, it can impede root penetration and airflow, potentially causing suffocation of roots. As it's heavy, it can restrict oxygen for the roots. 

So, as you can see, although sand can help with drainage, it's not usually the best choice as an alternative to perlite. You can mix a bit of sand with perlite and other growing mediums, but it's not as good as perlite for growing cannabis.

Alternatives to Perlite for Growing Cannabis

Perlite isn't an exotic material by any means and most people can access it easily. However, if you can't use perlite for some reason, you can go for other mediums that offer several advantages for growing cannabis. Here are a few substitutes:

1. Vermiculite

Vermiculite is a mineral that has various advantages for cultivating cannabis, especially if you want to enhance the quality of your soil and regulate moisture. Here are a few qualities that may appeal to you: 

Soil Aeration and Moisture Retention

Similar to perlite, vermiculite boosts soil aeration. Compared to perlite, vermiculite is better at retaining enough water for the roots, making it particularly beneficial for maintaining moisture in dry spells or highly draining soils. This attribute proves advantageous for cannabis plants when they grow rapidly or during the blooming stages when consistent hydration levels are crucial. Its structure is unique, with layers of thin particles that also retain the nutrients you provide while ensuring proper airflow in the soil. This feature helps prevent soil compaction and guarantees that plant roots receive oxygen and nutrients.

Lightweight and Sterile

Vermiculite is lightweight and sterile, making it an excellent choice for seed germination, propagation, and transplantation. In fact, since it holds the right amount of water, you can use it to grow seedlings and clones. To germinate cannabis seeds, the growing medium should always be moist. Vermiculite provides the perfect environment as it doesn't hold too much — just enough for the seeds to thrive. Its lightweight nature also makes it simple to move plants without harming their roots.

It blends easily with other growing media. Like perlite, it lowers the risk of introducing pathogens or pests into the growing environment. However, you may have to sterilize it if you're reusing it. 

That said, one con of using vermiculite is that you need to be careful not to overwater the plants. If you're growing a strain that doesn't like to grow in a medium that holds sufficient amounts of water for quite a long time, vermiculite may not be the best fit. Certain cannabis varieties tend to be prone to root rot and might not perform well in environments with extra moisture. In any case, do not use vermiculite as the sole medium to grow cannabis. By mixing it with coco coir or even soil, you will enhance the draining ability and also reduce the risk of overwatering.

In short, vermiculite is a good alternative to perlite, as long as you're cautious about not watering the plants too much. 

2. Rice Hull

Rice hulls are nothing but the protective layer of rice grains. Used to grow a variety of plants, you can use it to grow cannabis as well. 

One advantage of using it is that it's an environmentally friendly substitute for perlite in growing cannabis. Their distinct characteristics offer advantages for enhancing soil quality and promoting plant growth. Here is a detailed exploration of rice hulls and their uses in cannabis farming:

Improving Soil Structure

Rice hulls play a role in enhancing soil structure by loosening compacted soils and increasing air space. When incorporated into the soil they create pockets of air that encourage root development and improve absorption. 

As they break down, they gradually release nutrients and micronutrients enhancing the soil quality and supporting the growth of microorganisms. In essence, adding rice hulls can boost soil fertility and ensure the overall health of the soil, providing an ideal environment for cultivating cannabis plants. This enhanced soil structure also facilitates water penetration and reduces the risk of water saturation, resulting in stronger root systems and overall plant vitality.

Enhancing Aeration and Drainage

Similar to perlite, rice hulls boost soil aeration and drainage capabilities. Due to their porous nature, they promote air circulation within the soil, thereby preventing compaction while ensuring oxygen reaches the roots. This fosters root growth and helps prevent issues like root rot or nutrient imbalances associated with poor drainage.

The best part is that Rice hulls are eco-friendly, due to their biodegradable nature. Unlike perlite, which is extracted through mining processes, rice hulls are a byproduct of rice production and are sustainable. Thus, by using rice hulls, you're actually reducing waste. 

Rice hulls can also be used as mulch where you spread them on top of the soil to help regulate temperature, retain moisture levels, and prevent weed growth. Alternatively, you can mix them into your growing medium to enhance its structure, promote aeration, and improve drainage capabilities. Rice hulls are compatible with many types of soils and can be used to grow cannabis both indoors and outdoors. 

3. Pumice

Nature is so amazing that you can find various ways to grow plants if you know where to look. Pumice is one such medium that's formed when hot lava is cooled either by water or air. 

Pumice has gained a lot of recognition for its beneficial properties as gardeners are constantly looking for more sustainable ways to grow their favorite plants, and cannabis growers are no exception. 

Pumice is a versatile and efficient soil enhancer that works with many growing mediums. What makes it so efficient is its drainage and aeration abilities. Its porous structure contains air pockets that allow water to flow freely through the soil while maintaining oxygen levels for root respiration. This feature helps prevent waterlogging, reduces the risk of root diseases like rot, and supports nutrient absorption by plants.

One of the benefits of using pumice is its light weight making it convenient to handle and blend with soil or other growing mediums. Unlike materials like gravel or sand, pumice doesn't compress the soil, ensuring aeration and root growth. Moreover, pumice has a neutral pH, which means it doesn't significantly impact the soil's acidity, creating a great environment for cultivating cannabis plants.

Pumice remains stable for quite a long time in your growing medium. What's more, it doesn't deteriorate or lose its structure, so you'll have a consistent media as your growing medium for the entire life cycle of the cannabis plant. This means that you can reuse pumice for many more growing cycles and won't have to spend money looking for new mediums every time. 

While pumice excels at draining water from the soil, another huge advantage is that it can retain water as well. If you take a closer look at pumice, you'll notice that it has hundreds of microscopic pores that serve as sponges. These sponge-like pores retain water and release it when the plants need it, making it particularly useful if there's a dry spell or if you've forgotten to water the plants. 

However, unlike other growing mediums like vermiculite which has some risk of water-logging especially if you water a bit more, pumice doesn't cause water-logging issues. In short, it retains just the right amount of water for the plants to thrive. 

Last but not least, pumice can also help loosen compacted soil to improve the texture of your growing medium. So, if you add it to your growing medium, you'll end with a well-aerated, loose substrate that creates enough ventilation for the roots to penetrate easily and branch out. This encourages root growth, boosts nutrient absorption, and results in robust cannabis plants.

4. Coco Coir

If you've grown cannabis ever in either hydroponic or soilless mediums, you've definitely heard of coco coir as it's one of the most popular growing mediums after soil. 

In fact, growers now prefer Coco coir over soil because it offers various advantages and doesn't even come with the risk of soil-borne diseases. Naturally, it's one of the best alternatives to perlite.

One of the best advantages of using coco coir is that it drains water pretty easily. However, it doesn't drain everything, holding just enough water for plants to use it for a while. 

Another reason you may want to get some coco coir compared to other growing mediums is that the pH is pretty stable and doesn't fluctuate too much. 

Coco coir can be used on its own or combined with other mediums like soil, vermiculite, and perlite. It offers an amazing environment for root growth and microbial activity. However, coco coir goes through extensive processing before they are converted to blocks. Some manufacturers may supply coir with high EC that can cause problems to your cannabis plants. Thus, you have to purchase coir from a well-known supplier. 

5. Expanded clay pebbles

Known as hydroton or expanded clay pebbles, these are balls made from clay that has been fired in a kiln. These pebbles offer excellent drainage and serve as a stable hydroponic system base. They retain moisture and nutrients while ensuring oxygen circulation for plant roots. Additionally, they are eco-friendly and durable, making them an ideal choice for growing cannabis.

6. Rockwool

Rockwool is yet another popular growing medium, typically used by hydroponic growers. It's a type of mineral wool derived from basalt rock or slag. 

Most growers prefer rockwool not just due to its ability to retain water, but also because it aerates the medium to a great extent, providing proper support for plant root systems. 

The best part of rockwool is that you can use it as a standalone medium throughout the plant's life cycle. You just need to make sure that the plants have enough support and don't topple over. 

It is pH-neutral and durable, so you can reuse it as well. However, it takes a bit of preparation to use rockwool as you have to soak it in water before planting seeds, seedlings, or clones. 

Summary: Improving Cannabis Growth: A Guide to Perlite for Cannabis Soil

That’s it. You don’t need to do anything when adding perlite to your cannabis plant. Depending on what you want, you can either add 20% or 50% to your cannabis plant’s soil. And don’t hesitate to experiment a little until you find the right balance between perlite and soil. 

Perlite is an excellent soil amendment that can improve the quality of your soil quickly, making it more aerated and improving its drainage. Stay tuned to learn more about maintaining your cannabis soil.