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4 Easy Steps to Super Soil for Thriving Cannabis Plants

By Monica Mansfield | Last updated: May 12, 2021
Key Takeaways

Creating a rich substrate for your cannabis plants takes a little work up front, but in the long run can provide you with a thriving garden that doesn’t need your constant attention.

There are two ways to feed your cannabis: feed your plants or build your soil. You can buy bottles of fertilizer with impressive labels that you mix up in a nutrient solution for your plants, or you can build up healthy soil that will feed your plants every single time you water. Both ways work, and there are pros and cons to each method.

Bottled fertilizers can be expensive, and you usually end up investing in an entire line of nutrients that need to be purchased again and again. You have to take the time to measure and mix them properly every single time you feed so you have the correct PPM and pH. They are full of salts, so you’ll need to flush your plants on a regular basis. They do a great job, but they also create a lot more work throughout your garden’s life.

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When you build up your soil on the other hand, you put in the work up front to create a rich substrate that can sustain your plants through their entire lifecycle and then all you have to do is water. No mixing nutrients, no worrying about pH or PPM levels, and no flushing.

Super Soil

Probably the most well-known and effective soil for your cannabis plants first gained recognition in 2009. It was back then that the late Subcool, a famous cannabis breeder, released his Super Soil recipe in an issue of High Times magazine. The recipe quickly took off with hobby growers. I had many customers at my hydroponics shop come in and show me their successes with his recipe. The results were undeniable.

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There are a variety of super-soil recipes floating around the web and passed between growers. However, the general idea behind creating your own super soil is to add enough quality amendments to a soil base to feed your plants throughout their life cycle, and then compost the mixture for up to six months to a year before using it in your garden. This way, the soil and amendments have a chance to break down so the nutrients are readily available to your plants. The soil will feed your plants exactly what they need without you, the grower, having to worry about adding more nutrients or adjusting pH. Just add water.

(Read also: What’s Better: Growing Cannabis in Soil or Hydroponics?)

Super soil can be used indoors or outdoors with excellent results and is completely organic. It is as close to nature as you can get in an indoor grow room and gives your bud a delicious flavor and smooth finish. It is important to note you should not plant seeds and seedlings directly into your super soil because it might burn them. Start your plants in a soilless or less nutrient-dense mix, and then transplant into the super soil once they are a few weeks old.

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Grower scooping potting soil from a bag

Step One: Mix Your Base

When building your super soil, you’ll need to start with a base soil. You can buy bags of organic potting soil or make your own. The ingredients and nutrient profile of your base mix will determine which amendments, and how much of them, you’ll need to add next.

If you are making your own soil base, it may be worth getting it tested at a soil lab so that you know its exact nutrient profile and can choose your amendments accordingly.

There are many different soil recipes out there, but a general rule of thumb is to mix one to two parts compost, one part coco coir or peat moss, and one part perlite. Make sure to mix this thoroughly. Tarps and kiddie pools make good containers for mixing soil. This combination gives you a fluffy, rich base to build upon. You’ll need to make enough base soil to account for roughly 20-40 percent of the finished product.

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grower mixing amendments into soil

Step Two: Add Amendments

When you feed your cannabis plants from a bottle, you need to mix specific ratios of N-P-K during different stages of development. However, when you feed your plants through your soil, you just need to make sure the soil has enough nutrients to feed your plants during their lifetime. Cannabis needs nitrogen, phosphorus, potassium, and micronutrients, so you’ll need to add amendments to your soil that contain all of these.

Nitrogen-rich amendments include worm castings, crustacean meal, chicken manure, blood meal, neem seed meal, and bat guano. Phosphorus-rich amendments include crustacean meal, bat guano, chicken manure, bone meal, and rock dust. Potassium-rich amendments include worm castings, azomite, geensand, kelp meal, and wood ash.

  • Worm castings provide a quick-release form of nitrogen and also contain many micronutrients and beneficial microbes.
  • Crustacean meal is slower to release nutrients and contains nitrogen, phosphorus, and calcium to your mix. It also contains chitin, which supports the beneficial microbes that kill harmful nematodes.
  • Chicken manure is full of nitrogen and phosphorus. It is “hot” and needs time to compost or it can burn your plants.
  • Blood meal is very high in readily available nitrogen and can burn your plants if you add too much, so use it sparingly.
  • Neem seed meal is a byproduct of the neem industry that is high in nitrogen and it helps to combat soil pests.
  • Bat guano provides very high levels of nitrogen and phosphorus.
  • Bone meal is a good source of phosphorus and calcium and is usually made from cattle bones, although you can also buy fish bone meal. It needs the overall pH of your soil to be below 7.0 for it to be effective.
  • Rock dust is a slow-release source of phosphorus that will feed your plants for years. It also needs to be in soil below a pH of 7.0 to be effective.
  • Azomite is an ancient volcanic dust that contains potassium and more than 60 trace minerals. It should be used sparingly as it can raise pH levels.
  • Greensand is a rich source of potassium, and also contains calcium, magnesium, iron, phosphorus, and more than 30 trace minerals. It releases nutrients slowly over time and improves soil tilth and drainage.
  • Kelp is made from seaweed and adds potassium and more than 60 elements and micronutrients to the soil.
  • Wood ash is a good source of potassium along with other trace minerals. Use it sparingly because it can raise the soil pH to the point of nutrient lock out.


roots treated with mycorrhizae

Step Three: Establish Fungal and Bacterial Population

The key to nutrient uptake and absorption is making sure your soil has established fungal and bacterial colonies. These microbes break down nutrients into forms your plants can use. They also protect your plants from disease. If you are growing in the ground outdoors, beneficial fungi will create an underground network, bringing nutrients to your plants from miles away. Many of the amendments you’ve already added will help with this, such as compost, worm castings, bat guano, and kelp.

(Read also: The Power of Mycorrhizal Inoculants on Indoor Cannabis Crops)

You can also purchase mycorrhizal inoculants. These powders are dormant microbes that are reactivated in the soil when watered. The sooner you establish these colonies, the larger they will become and the more helpful they are towards your plants.


compost bins in a garden

Step Four: Compost

Once your soil is mixed thoroughly, you’ll want to add some water and let it sit and bake in the sun for up to a year. Some people recommend letting it sit for 30-60 days, while others recommend six months to a year. The longer you let it sit, the more it will break down, and the more available the nutrients will be to your plants. So, if you have the time, let it sit for at least six months.

Put your super soil in clean garbage cans with a lid and set them outside in a sunny location. Add enough water so that your soil is moist but not wet as this will help to activate the microbes. Be sure not to use water that has chlorine in it, which is common in city water. This will kill your microbes and totally defeat the purpose of making your own soil. If you are on city water, you can set a bucket of water out overnight and let the chlorine evaporate before using it.

If you are looking for a way to lighten your gardening workload and grow organically, building your own soil might be right for you. You can create your own super soil that will grow healthy, flavorful, potent cannabis plants, and all you need to do is add water.

(Read next: Subcool: Remembering a Cannabis Legend)

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Written by Monica Mansfield | Homesteader, Owner & Writer of The Nature Life Project

Profile Picture of Monica Mansfield

Monica Mansfield is passionate about gardening, sustainable living, and holistic health. After owning an indoor garden store for 5 1/2 years, Monica sold the business and started a 6.5-acre homestead with her husband, Owen. She writes about gardening and health, as well as her homestead adventures on her blog at thenaturelifeproject.com.

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