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Best soil for cannabis: What every grower should know

Theo Gardner
June 17, 2024
β€’
10 min read
A grower holding some of the best soil for cannabis.
A grower holding some of the best soil for cannabis.
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Growing cannabis can be incredibly rewarding, but it all starts with the right foundation - soil. 

Choosing the best soil for cannabis is crucial for healthy plants and high-quality yields. 

In this post, you'll learn everything you need to know about selecting and preparing the best soil for cannabis plants.

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

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Understanding soil for cannabis plants

In cannabis cultivation, soil is more than just dirt. Natural soil is a living ecosystem, a growing medium full of beneficial bacteria and beneficial microbial life that help your plants flourish. 

Unlike artificial growing mediums like coco coir (made from coconut husks), cannabis soil provides a natural environment that supports plant growth. Although similar, coco coir lacks the nutrients and beneficial microorganisms found in soil.

The best soils for indoor cannabis offer a stable environment, making it easier for cannabis growers to manage their plants’ pH levels and nutrient intake. 

Understanding the components and benefits of the best cannabis soil sets cannabis growers up for success.

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Benefits of using the best soil for cannabis

Using the best soil for growing cannabis has many advantages, including significantly improving your growing experience and the quality of your plants.

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Cannabis soil microbes.

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1. Microbial life

Good cannabis soil is teeming with beneficial microbes. These microorganisms help break down organic matter, releasing nutrients your plants can easily absorb. 

This natural process promotes healthy root development and robust growth. 

The presence of beneficial microbes in soil enhances root growth and the overall health of your plants and boosts nutrient uptake.

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Some cannabis flowers grown in the best soil for cannabis.

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2. Quality of product

Many cannabis growers find that cannabis from healthy cannabis plants grown in quality soil often has a richer flavour and aroma compared to plants grown in hydroponic systems. 

The complex interactions between soil quality, nutrients, and microbes contribute to the production of terpenes and cannabinoids, which enhance the overall quality of buds. 

The rich organic matter in soil for growing cannabis helps produce high-quality buds with superior taste and smell, making your final product more enjoyable.

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A PH meter in some cannabis pots.

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3. Easier pH management

Soil naturally buffers pH levels, making it easier to maintain the slightly acidic soil environment that cannabis plants require. 

Unlike hydroponic systems, which require constant monitoring and adjustment of pH levels, the right cannabis soil can help keep pH fluctuations in check. 

This buffering capacity makes high quality soil for growing cannabis a forgiving medium for beginners who may not have the tools or experience to manage pH precisely.

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A cannabis plant that doesn't have enough soil nutrition in the pot.
This plant needs a bigger pot or more nutrition.

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4. Nutrient retention

Depending on the size of your pot or growing space, you might not need to add many nutrients. 

High-quality, nutrient rich soil often contains enough nutrients to support your plants through most of their life cycle, reducing the need for frequent fertilisation. 

Soils rich in plant nutrients, especially those containing organic materials like compost and earthworm castings, provide a steady supply of essential elements like nitrogen, phosphorus, and potassium.

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5. Organic growing

Many growers prefer organic methods, and natural soil is ideal for this. Organic soil for cannabis can be enriched with compost, earthworm castings, and other natural cannabis soil amendments to create a rich, living environment for your plants. 

Organic cannabis soils support a healthy ecosystem, encouraging the growth of beneficial bacteria and fungi that aid in nutrient absorption and plant health. 

Using organic soil for cannabis plants indoors benefits your plants and the environment by reducing the need for synthetic fertilisers.

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A grow buying the best soil for cannabis at a grow shop.

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6. Availability

Soil is readily available at garden centres and online. High-quality compost and soil mixtures explicitly designed for cannabis are also easily found, making it a convenient choice for growers. 

These pre-made mixes are often tailored to the needs of cannabis plants, ensuring favourable growth conditions. 

Additionally, you can amend and customise these soils with additional nutrients and organic matter to suit your specific growing style.

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7. Convenience and simplicity

Using soil is straightforward and accessible, making it an excellent choice for novice growers. 

Soil's natural structure and nutrient content provide a stable growing environment that requires less intensive management than hydroponic systems. 

Soil growing can also be less costly in the long run, as it doesn't require the same level of investment in pH meters, nutrient solutions, and other equipment needed for hydroponics.

Using soil provides a natural and robust growing medium that supports healthy cannabis plant growth, high-quality yields, and a more enjoyable cultivation experience.

If you are keen to learn how to up your growing game, sign up for the Grow The Best newsletter now!

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Drawbacks of using soil for cannabis growers

While soil is an excellent medium for growing cannabis, it does come with some challenges that you should be aware of.

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Some over watered cannabis plants.
These plants are overwatered and are to cold.

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1. Overwatering risks

Soil can retain water, which is beneficial for plants, but also poses a risk of overwatering. 

Overwatering can lead to root rot and other issues when growing in soil. It's essential to manage your watering schedule carefully to avoid these problems. 

Good drainage is crucial to prevent water from stagnating and causing problems at the root system.

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Spider mites on a cannabis leaf.
Spider mites on the underside of a cannabis leaf.

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2. Pest issues

Soil, especially if homemade, can harbour pests. Bugs and insects can find their way into your growing environment, potentially harming your plants. If you make your own soil, you must be vigilant about pest prevention and control. 

Using sterilised soil or baking your soil mixture can help reduce the risk of introducing pests, but then you’ll need to reintroduce beneficial microbes, which will require more work and additional cost.

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An underfed cannabis plant.

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3. Nutrient limits in small pots

When growing in smaller pots, the soil can only hold a limited amount of nutrients. This means you might need to supplement with additional cannabis nutrients for soil as your plants grow. 

Monitoring the nutrient levels in smaller containers is essential to ensure your plants get what they need. 

Amending soil for cannabis with things like like earthworm castings and bat guano can help maintain nutrient levels.

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A soil mix for growing cannabis.

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4. Uncertainty in homemade mixes

Making your own soil mix can be rewarding but also comes with uncertainties. You might not always know the exact nutrient content or the presence of unwanted substances like heavy metals. 

Commercial soils are often tested and balanced, providing a more reliable option. 

If you create your own cannabis soil mixture, ensure you source high-quality ingredients.

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5. Potential for heavy metals

Homemade soil mixes can sometimes contain heavy metals, which are harmful when smoked. Ensuring your soil components are clean and safe is crucial for a healthy crop. 

Regular testing of your cannabis soil can help avoid contamination and ensure a safe product.

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6. Messiness of supplementation

Adding nutrients to the soil to prevent nutrient deficiency can be messy. Many organic nutrients are sugar-based and can be sticky and smelly. Proper storage and handling of these nutrients are necessary to maintain a clean growing area. 

Organic soil amendments for cannabis, like bone meal and coco coir, can also be challenging to manage due to their texture and consistency.

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A cannabis plant in very dry soil.

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7. Hydrophobic soil issues

Over time, soil can become hydrophobic, meaning it repels water. This often happens if the soil dries out completely. 

Rehydrating hydrophobic soil can be difficult and requires careful attention to watering practices. 

Using wetting agents or incorporating ingredients like coco coir can help maintain moisture levels.

Despite these challenges, many growers prefer soil for its natural benefits and ease of use. By understanding and addressing these potential issues, you can create a thriving environment for your cannabis plants.

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Creating your own cannabis soil mix

Making the best soil mix for cannabis allows you to customise the nutrient content and texture to suit your plants' needs. Here’s a basic recipe to get you started:

Basic cannabis soil recipe:

  • 1 part compost
  • 1 part coco coir or sphagnum peat moss (for better water retention). Just make sure to pay attention to your pH ranges depending on compost and other inputs.
  • 1 part perlite or vermiculite (for improved drainage)
  • 1 cup of earthworm castings per 19L (5 gallons) of soil
  • 1 cup of bat guano 19L (5 gallons) of soil
  • 1 cup of bone meal 19L (5 gallons) of soil
  • 1/4 cup of gypsum and agricultural lime or oyster shell flour per 19L (5 gallons) of soil
  • 1/4 cup of agricultural lime or oyster shell flour per 19L (5 gallons) of soil

Steps to prepare the mix:

  1. Combine all ingredients in a large container or mixing area.
  2. Thoroughly mix until all components are evenly distributed.
  3. Add water to moisten the mixture slightly and activate the microbial life in the compost and worm castings.
  4. Let the mix sit for a few days to a week before using it to plant your cannabis.

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An illustration showing N, P and K values for soil.

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Adding organic supplements:

To ensure you’ve got the best soil mixture for cannabis, keep your soil mineralised and nutrient-rich by adding organic supplements like kelp meal, fish meal, or alfalfa meal. 

These supplements provide additional nutrients and help sustain microbial activity in good cannabis soil.

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A grower adding vegetables into their compost bin.

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Using homemade compost:

Homemade compost is a fantastic addition to your soil mix. However, it might contain pests or pathogens. 

Check and manage your compost pile regularly to ensure it’s healthy. Compost tea, made from compost and water, can enrich your soil and keep beneficial microbes alive.

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A grower making compost tea in a large container.

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Compost tea:

Compost tea is a liquid solution made by steeping compost in water. It’s full of beneficial microbes that boost soil health and plant growth. To make compost tea:

  1. Fill a container with water.
  2. Add a small bag or sock filled with compost.
  3. Add an airstone to aerate the water.
  4. Let it steep for 24-48 hours, stirring occasionally.
  5. Use the resulting liquid to water your plants, ensuring they get a dose of living microbes.

Sterilising soil:

If you’re worried about pests in your soil, you can sterilise it by baking. Spread the soil on a baking tray and heat it in an oven at 180Β°C for 30 minutes. 

This process kills harmful insects and pathogens. After sterilising, reintroduce beneficial microbes by adding compost tea or fresh compost.

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A close up of lots of worms in a rich cannabis compost.

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What is super soil for cannabis?

Super soil is a nutrient-rich organic soil mix designed to provide cannabis plants with everything they need for optimal growth. 

It typically contains a blend of high-quality compost, earthworm castings, bat guano, bone meal, blood meal, fish meal, rock phosphate, kelp meal, and other organic amendments. 

These ingredients work together to create a living ecosystem that supports healthy plant development and robust yields.

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How do I make my own super soil mix?

To make your own, follow this cannabis super soil recipe:

Base mix:

  • 1 part high-quality compost
  • 1 part coco coir or peat moss to regulate soil moisture 
  • 1 part perlite to mitigate poor drainage

Nutrient amendments:

  • 1 cup of earthworm castings per 19L (5 gallons) of soil
  • 1 cup of bat guano per 19L (5 gallons) of soil
  • 1 cup of bone meal per 19L (5 gallons) of soil
  • 1 cup of blood meal per 19L (5 gallons) of soil
  • 1 cup of fish meal per 19L (5 gallons) of soil
  • 1/2 cup of rock phosphate per 19L (5 gallons) of soil
  • 1/2 cup of kelp meal per 19L (5 gallons) of soil

Mineral amendments:

  • 1/2 cup of dolomite lime per 5 gallons of soil
  • 1/2 cup of azomite or other rock dust per 5 gallons of soil

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Mix all the ingredients thoroughly and moisten the mixture. Let it sit for at least 30 days to allow the nutrients to break down and become available to your plants.

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What is the difference between super soil and living soil?

Super soil is a type of soil specifically formulated to be a highly nutrient-dense medium that supports cannabis throughout its entire growth cycle without the need for additional fertilisers.

It supports indoor cultivation right through from planting cannabis seeds, the cannabis seedlings stage to the vegetative phase and flowering stage.

Living soil, on the other hand, focuses on maintaining a healthy ecosystem of microorganisms that continuously break down organic matter to release nutrients. 

While both promote robust plant health, super soil is often considered more self-sufficient, whereas living soil requires ongoing care to maintain its microbial balance.

An organic super soil mix ensures that your cannabis plants receive a balanced diet of nutrients, leading to healthy growth and high-quality yields.

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Managing soil for ideal growth

To ensure your cannabis plants flourish, managing your soil effectively is essential.

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Good drainage and moisture retention:

Aim for a good soil texture. Clay soils and sandy soil are too far at either end of the spectrum. 

Good drainage is essential to prevent waterlogging, which can lead to root rot. Adding perlite or vermiculite (a naturally occurring mineral) helps maintain the right balance of air and water in the soil.

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Nutrient levels:

Check the nutrient levels in your soil regularly, especially if you’re growing in smaller pots. 

Organic amendments like compost, worm castings, and bat guano can replenish depleted nutrients. Liquid fertilisers and compost tea are also excellent for maintaining nutrient levels.

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Controlling soil pH:

Cannabis plants prefer slightly acidic soil with a pH of 6.0-6.5. Use dolomite lime to raise the pH or elemental sulphur to lower it. 

Test your soil pH regularly and adjust as needed to ensure optimal nutrient uptake.

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Best soil options for indoor cannabis growing

For indoor growers, selecting the best soil is crucial for a successful harvest. Here are some top options:

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Top pre-made soil brands:

Kis Organics Biochar soil. The best soil for cannabis.

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  1. Kis Organics. A premium soil. It offers all the rewards of Water Only soil with the added benefit of Biochar at 8% of total media. 
  2. Biobizz All-Mix. It contains a rich blend of organic amendments and beneficial microbes, promoting healthy growth and robust root development. This soil mix provides a nutrient-rich environment, ideal for all stages of cannabis growth.
  3. Canna Terra Professional. It is a high-quality soil mix known for its excellent drainage and aeration properties. It is enriched with essential nutrients and organic materials, ensuring optimal growth conditions for cannabis plants. This soil is suitable for both beginners and experienced growers.
  4. Plagron Grow Mix. A well-balanced soil blend that includes perlite for improved aeration and drainage. It is pre-fertilised with organic nutrients to support the initial stages of plant growth. Plagron Grow Mix is ideal for those who prefer a simple and effective growing medium.
  5. BioBizz Light-Mix. For those who want more control over nutrient levels, BioBizz Light-Mix is an excellent option. It provides a lightly fertilised base, allowing growers to customise feeding schedules with additional nutrients. This mix is perfect for seedlings and young plants.
  6. Ecothrive Eco-Life Soil. A living soil packed with organic nutrients and beneficial microbes. It is designed to support the entire life cycle of cannabis plants, from seedling to harvest. This soil is ideal for growers looking for a sustainable and organic growing medium.

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Best potting soil for cannabis:

Look for potting soil specifically designed for cannabis. A potting mix usually contains the right balance of nutrients, aeration, and water retention to support your plants.

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Organic vs. non-organic options:

Organic soils are enriched with natural amendments and organic substances like compost and worm castings, promoting a healthy, living soil ecosystem. 

Non-organic soils may include synthetic fertilisers, which can provide a quicker nutrient release but lack the microbial benefits of organic options.

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Soil care and pest prevention when growing cannabis in soil

Keeping your soil healthy and pest-free is vital for the success of your cannabis plants.

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Common soil pests:

Soil can attract pests like fungus gnats, root aphids, and spider mites. Regularly inspect your plants and soil for signs of infestation. Sticky traps and natural predators like nematodes can help manage pest populations.

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Sterilising soil:

As mentioned earlier, sterilising your soil by baking can eliminate harmful insects and pathogens. However, this process also kills beneficial microbes, so you’ll need to reintroduce them using compost tea or fresh compost.

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Maintaining healthy soil life:

Keep your soil rich in organic matter and beneficial microbes by regularly adding compost, earthworm castings, and other organic amendments. Avoid over-fertilising, which can harm microbial life and lead to nutrient imbalances.

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Takeaways

Choosing the best soil for cannabis is crucial for healthy plants and high-quality buds. 

Soil is an excellent medium for beginners because it’s easy to use and supports organic growing. 

Start with a good-quality cannabis compost or soil mix, and use organic nutrients as needed.

Experiment with different soil mixes and amendments to find the optimal soil that works best for your growing style. 

By understanding and managing your soil, you’ll ensure your cannabis plants thrive and produce a bountiful harvest.

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Happy growing!

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Theo Gardner
June 17, 2024
β€’
10 min read

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