Can You Reuse Soil for Cannabis? How to Recycle Soil, Coco and Perlite

Yes, you can reuse soil and coco for your next cannabis grow, as long as you clean it, sterilize it and amend it first. Pull out old roots, flush out leftover salts and nutrients, kill off pests and pathogens (with boiling water, sun pasteurization or peroxide), then add fresh compost, coco or perlite. Out in the ground, the soil itself supplies plenty of minerals and nutrients, but in a grow room you'll need a rich growing medium plus added nutrients. Indoors, you can reuse lights, fans, containers and even your growing medium if you treat it right.

This time we're talking about reusing your growing medium and what to keep in mind when you do.

What should you know about growing media for cannabis?

Your growing medium is whatever your plant grows in. Options include soil, coco coir, rockwool, grow stones, clay pebbles and perlite, among others. Some media aren't worth reusing (rockwool cubes, for example, get so compacted that they're hard to clean and sanitize between grows), but many others are.

Still, reusing a growing medium isn't as simple as fluffing it up and starting over. If you want your next grow to thrive, you need to clean and sanitize the medium and amend it as needed.

How do you reuse cannabis soil?

Just like you clean and sanitize your grow room between cycles, you need to clean and sanitize your soil. Cleaning flushes out leftover nutrients and salts and makes it easier to figure out what your next crop will need. It also gets rid of debris like old roots and fallen leaves so new roots can grow freely. Sanitizing, on the other hand, kills pathogens, pests and their eggs.

Here's the step-by-step:

Make sure your homemade soil is clean

If the soil was hit by a pathogen or is in bad shape, toss it, because if you reuse it or mix it into compost, you could spread that pathogen through your whole grow. And this is a big one: wash your hands well with hot water and soap before touching soil, healthy plants and containers.

Use lots of water

To flush leftover nutrients and minerals out of your medium, use plenty of water and a flushing solution. Repeat this 2 or 3 times. If your last grow had pests, rinse the medium with boiling water, and if there was mold, add an antifungal to the water.

Get rid of weeds

To wipe out weeds and their seeds, insect eggs and fungal spores, put your old soil in a black garbage bag and leave it in the sun for an afternoon. The heat pasteurizes the soil, and then it's ready to reuse. Heads up, though: this can also kill off nutrients and beneficial bugs, so if you pasteurize, plan to amend the soil afterward.

Can you reuse potting soil from containers?

Honestly, there's no great answer here, because bagged potting mix is pretty much spent once it's been used. In-ground grows usually recycle their soil naturally about a year after harvest. If it's been less than a year, the soil won't have any minerals or nutrients left.

What is coco coir good for, and how do you reuse it?

Coco coir is recycled, processed fiber from coconut husks. These days it's an excellent growing medium for cannabis, with a pH between 6.5 and 7.0, which puts it on par with unfertilized soil.

To cut down on waste, here are some tips for reusing coco coir.

• Break up the coco and pull out any loose roots.
• Soak the coco in an enzyme solution to break down the smaller roots you can't pick out by hand.
• Rinse the coco with distilled water to wash out debris and leftover salts.
• Sterilize the coco with hydrogen peroxide (35% stock, always diluted according to the label).
• Top it off with some fresh coco and you're good to go.

How do you reuse perlite?

Perlite starts life as obsidian, a volcanic glass that forms naturally when lava cools. When obsidian absorbs water over time, it turns into perlite.

Raw perlite looks nothing like the stuff you buy at the store, because manufacturers crush it and heat it to around 980 °C (1,800 °F) so it softens and pops like popcorn.

To recondition a used growing medium, you'll need to work in a few different ingredients, plus some fertilizer. That adds nutrients, balances pH and aerates the medium.

That's where perlite comes in. It's an inert material that doesn't break down easily, though it does compact and change shape over time. So it's worth adding when you
recycle your medium, since it improves aeration and helps with water retention. Add it until it makes up 5% to 10% of the total mix.

Reusing indoor growing media: what else should you know?

On top of possibly being contaminated, reused soil has no nutrients left. Before you use it again, amend it with things like compost and peat.

If you don't want to go through all that, you can let nature do the work for you. Dump your old cannabis soil into your compost bin and let the microbes break down the roots and everything else for a year, then use it down the road.

Another option is spreading old soil straight onto your garden beds. Break it up and rake it over the beds to add organic matter that will break down into nutrients for your plants.

 

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