Whether you are growing indoors or outside, one thing is certain: you’re going to need soil and lots of it. Traditionally, growers have been told to use new soil after each harvest, and this is advice that gardeners of all types are used to hearing. But it’s an expensive ritual, and it isn’t always necessary.
Great soil is comprised of three main components: a light substance like coir or peat moss to help with water retention and aeration, non-synthetic or organic nutrients to feed the plants, and compost to provide a nutrient-rich foundation for your soil’s ecosystem. Healthy soils are home to microbial life that aids in the breakdown of organic matter for plant consumption and provides organic protection from pathogens and pests.
Is it possible for recycled soil to be as healthy as new soil?
Despite the resignations many growers have about reusing soil, the answer is yes. In fact, the term “Recycled Organic Living Soils” (ROLS) refers to an entire organic cannabis cultivation movement that incorporates various organic farming techniques including those which reuse soil.
Reusing soil and practicing organic farming were old hat before chemical fertilizers and pesticides became the gold standard in the mid-twentieth century. While those chemicals produce immediate results, they leave behind long-term deficiencies. Synthetic substances can be lethal to the microbial life that makes a soil’s ecosystem so resilient, rendering the plants rooted in it vulnerable to pathogens and pests. Pesticides used to counter those vulnerabilities can be dangerous for the environment and for humans, and they may render your cannabis too toxic for consumption, especially for medical patients. Although chemical nutrients seemingly super charge plant growth, they do nothing to facilitate the symbiotic relationship that naturally occurs between plants, the soil, and the organisms living in that environment.
When done properly, reusing soil is kind of like aging wine—with time, it only gets better.
If ROLS is so great, why isn’t everyone doing it?
It isn’t easy. You will definitely save money if you reuse your soil, but you will also put in more labor than you would have if you just used new soil each harvest. At the same time, some argue that once you’ve created an extremely healthy medium, it requires much less maintenance—just occasional amendments. Practice makes perfect, though, and only you know the time that you can afford to spend on practicing the methods needed for proper soil recycling.
Additionally, reusing soil doesn’t come without risks. The composition of soil changes throughout the season. By the end of harvest, your soil will contain leaves, roots, insects, weeds, and potentially harmful pathogens. Additionally, the reason you choose soil with the proper nutrients is so that those nutrients would satisfy your plants’ appetites. A healthy, bountiful harvest indicates that you got your nutrients right… and that your soil is now probably depleted of most of them.
Finally, cannabis cultivation has been through the political wringer in the United States for almost two centuries. It has been federally prohibited for most of that time, so the industry hasn’t had a lot of space to figure out its best practices. For example, there still isn’t a universal standard when it comes to cannabis testing even though the research demonstrates a need for consistent and thorough independent lab tests. A lot of what people believe about cannabis cultivation has been passed down by word of mouth. Yes, there are scientists and agricultural experts studying all facets of this incredible plant, but as long as cannabis remains a schedule 1 drug, or a federally illegal substance considered dangerous and medically useless, researching the healthiest methods of cultivation and distributing that knowledge will remain unnecessarily challenging.
How to make ROLS
Consider the following as general guidelines for making your own ROLS. Ultimately, it will take trial and error for you to figure out exactly what your strains need and what materials you prefer.
Get your hands on some good, organic soil.
You can buy soil from any home improvement or gardening store. Keep in mind that the soil you are purchasing has probably been sterilized via heat treatment, so while it is free of pathogens, it is also pretty void of life. Think of it as a blank canvas. You will have to supplement it in order to create a healthy soil ecosystem for your plants.
Incorporate ingredients to enhance aeration.
Soil needs to be broken up to increase water absorption and ventilation. Peat moss or coir are commonly used for this purpose. Peat moss comes from peat bogs, and some people worry that its use is unsustainable since its matter comes from decomposed plant material accumulated over thousands of years. While it is technically a renewable resource, it takes a hot minute to renew. On the other hand, coir comes from coconuts, a resource that is far more renewable. Coir tends to hold more water than peat, but because of that, you will have to watch for salt accumulation. Coir also tends to have a better pH whereas peat tends to be acidic.
Add a mix of organic fertilizers.
An excellent source of nutrients and healthy bacteria is vermiculture, or the use of worms in cultivation. Worms create compost, and you can easily create a worm composting system in which you discard your organic waste material (rinds, old produce, leaf trimmings, roots, etc.) and let the worms have at it. In addition to forming compost, the worms will also leave behind their very nutrient-rich poop (castings). If worm poop freaks you out, you can try bat poop (guano), chicken poop (manure). Bone meal, blood meal, fish meal, and kelp are also good organic options. Each of these has its own advantages and disadvantages, so do your research based on the nutrients you believe your strains need.
Protect your plants with organic pesticides. Stinging nettles, orange peel, lemon peel, onion, and neem oil, are all safe, natural pest repellants. Synthetic pesticides typically don’t distinguish between beneficial organisms and dangerous ones, but these sources do.
How to Reuse ROLS
One of the primary benefits of using ROLS in the first place is its reusability. The microbial life within it makes it easy to use again with a little maintenance. The biggest concerns growers have are nutrient depletion and pathogens. Here are a few solutions.
Before getting into how to reuse the soil, it’s best if you know that you probably shouldn’t use soil that has produced diseased plants.
Clean it up.
Remove roots, leaves, insect eggs, and any matter that accumulated during the harvest.
Place the clean soil in black garbage bags and let it bake in the sun. The heat will pasteurize the soil, killing off diseases.
If you use worms to compost, add the soil to your worm bin and let the worms do the work. They will add the nutrients and microbial life your soil needs to feed your plants and ward off diseases.
Similarly to adding the soil to your worm bin, you can add the soil to your compost heap. The heat of the composting process will rid the soil of any pathogens.
You can replenish the nutrients in your soil by spraying it with compost teas.