Recycled Organic Living Soils: The Right Way to Reuse Soil

Baby marijuana plant emerging through the soil

Over the last couple years there’s been a lot of buzz in the cannabis cultivation community surrounding living soil. Many are left wondering what it is and how it’s different from other production methods. 

What is Living Soil?

Living soil refers to an organic growing method based around keeping the soil food web intact by replacing tilling with mulching. Vibrant soil life provides benefits to the cannabis root system — better soil structure, drainage and water retention. This can mean lower costs and better yields and quality for the cannabis farmer. 

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Cannabis growers simply continually apply organic matter to the surface keeping all the life below intact and in balance. The most crucial part is to maintain soil cover at all times otherwise weeds can establish and overtake the cannabis. For more info on attributes of different mulches, check out this resource

Although the method sounds simple, growing cannabis in living soil requires in-depth knowledge of soil food web and plant physiology. Skills like insect ID, research, combined with real experience and a caring mentor or consultant can help cannabis growers make the transition from a conventional nutrient system with soaring success. 

Beneficial companion plants and cover crops are often planted in with cannabis to attract and support beneficial insects and outcompete weeds, and a thick layer of organic matter is applied to smother weeds and feed the existing microbiome. Choosing a mulching material often depends on what is readily available near your garden site at an affordable price. 

Outdoors it is fine to use a bulky mulch like straw and fallen leaves but indoors or greenhouses where container space is limited, high quality hot compost or screened worm castings is ideal combined with intercropped cover crop to provide food for beneficial insects.

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This technique works on small cannabis farms and indoor grows because it requires no equipment making it useful for those just starting out their gardens.

Why Use Living Soil in Your Cannabis Garden?

Not only will your yields improve over time, your flower quality will increase, this means higher terpene percentages, and higher CBD and THC percentages. In the current market this means more money in the growers pocket. Many conventional cannabis growers spend additional time and money applying additives to mimic the quality inherent to cannabis grown in living soils. 

In conventional cannabis gardens, soil organic matter (SOM) content decreases over time and must be specifically addressed by adding compost to keep soils from eroding and becoming less productive.

In a living soil system, SOM actually increases over time because adding mulch is integral to making the system work. It may take a few years for transitioned soils to reach peak production, and in the meantime adding amendments will insure good yields. 

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 In nature, to obtain nutrients, plants actually curate soil life to suit their purposes. Exudates from their root zone are targeted to feed and proliferate specific soil microbes to breakdown needed nutrients giving the plant exactly what it needs when it needs it in a mutual symbiotic relationship, this is the process tapped into by growers using living soils.

Growing cannabis in living soil requires the grower’s commitment to use mulch to vitalize the soil instead of tilling or changing potting soil with every run. There is a significant focus on feeding soil life using strictly organic inputs with few exceptions. To ensure a solid yield, cannabis growers spike or top dress amendments, worms, nematodes, and sometimes liquid teas on a schedule through the growing cycle. More life means more available nutrients, proteins, and sugars in your organic soil matrix and this translates to faster growth rates and higher yields. In living soil systems, the goal of the cannabis grower is to facilitate and steward these natural processes to obtain a yield equal to or in excess of what could be expected in a conventional systems. 

While the research pertaining to cannabis yields and crop performance in living soils is spotty, in some cases, growers of traditional food crops have reported 76% higher profits in regenerative agriculture systems while tolerating a yield drop of 30%.

 Though this can pencil out, I highly recommend keeping your yield goals comparable to conventional gardens, and in time, with proper management it is possible to see better yields. Many organic cannabis farms accept lower yields as part of the cost of operating, even if this is the case, living soils can still help small scale farmers become more profitable. 

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How to Make Living Soil Work for Your Outdoor Cannabis Garden

Test Soil

Get a soil test to understand how your native soil measures up to what cannabis requires. Usually the lab will provide a general guide for amending your soil, if you need to be discrete, tell them you are growing tomatoes as the nutrient and pH requirements are similar.

Apply pH Adjusters, and Cover Planting Area

In fall ideally, apply pH adjusters before covering the desired planting area with light excluding tarp for several months. Mulch can be used instead of plastic but it must be thick enough to smother any weeds. For a small area, it is safest to smother any live vegetation with cardboard and top with thick mulch to ensure it doesn’t survive.  This should result in a bare ground by spring, perfect for topping with mulch or starting a spring cover crop —all with no digging or tilling. If you are lucky enough to start with a blank slate, try an overwintering cover crop suited to your area. Engineer your choice of cover crops to match the additional nutrients needs of your crop to save additional money on inputs. 

Pick your Mulch

 Decide on the type of mulch you want to use and apply a 3-6 inch deep layer in spring after adding any amendments to get the season started.

Use Nutrient Spiking

For spring planting, it is most useful and cost effective to use nutrient spiking as this keeps your amendments in the root zone where your plant can easily access them without competing with neighboring plants. 

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Apply Top Dressing (Supersoil)

After spiking amendments, growers can continue to apply top dressing every several weeks and mulch as needed throughout the season to suppress weeds, build soil and feed microbes. If spikes are designed to last through the flowering cycle, this is often referred to as ‘supersoil’ so providing additional top dressings of nutrients is not necessary. There is great potential for reduced labor costs with supersoil, but sometimes problems can arise. Combat any issues by using your extra time to closely monitor growth and identify any issues early. Usually these are rare in living soils but the key to problem prevention is keen observation. 

Watering is Very Important

Dry conditions kill soil life so in general you want to keep more moisture in your root zone than when running a conventional garden however your soils will naturally hold more moisture for longer so you should have to water less overall.

Implement an IPM (Integrated Pest Management) Program. 

This will be one of the cornerstones of the success of your garden. Chemicals relied upon by the conventional gardener to keep things in check, disrupt beneficial predatory insects and microbes needed break down nutrients and are not typically used or needed in living soil systems. See some examples of different biological controls here.

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Special Considerations for Using Living Soils Indoors or in a Greenhouse

Planning and scheduling beneficial predatory insect applications for your plant canopy as well as the root zone is crucial— especially during the first few cycles with your crops. Interplant cover crops designed to support the beneficial insect community as many species need flower nectar to complete their life cycles. If the insects are able to reproduce in your indoor environment you will save time and money on buying and applying new populations. 

Find a reputable biocontrol company that will help you stay on top of it with preventative maintenance, they will also advise what to plant to keep the populations going. Most good companies will provide recommendations for corrective biocontrol treatments if things get out of whack with a pest or disease outbreak. 

Pro Tip: because of the cost associated with weeding and insect control it makes sense to spend the extra money to buy high quality mulches like screened worm castings and hot composted compost, free of pests and disease. Use trusted brands so you aren’t introducing new weed seeds and potential harmful insects common with homemade cold compost. Also adding up to 3% activated carbon in your containers will help keep nutrients from leaching during watering.

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Additional Resources: 

https://www.motherearthnews.com/store/product/the-organic-no-till-farming-revolution

https://extension.umn.edu/how-manage-soil-and-nutrients-home-gardens/living-soil-healthy-garden

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https://www.kisorganics.com/blogs/news/basics-to-mixing-your-own-soil

https://www.uvm.edu/sites/default/files/Extension-Master-Gardener/improvinggardensoilswithcomposting.pdf

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