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Using Poop As Cannabis Fertilizer

When trawling the internet for articles about cannabis cultivation, you’ll probably find some of them are great, and some of them are sh*t. This one is both! Yes, you can use poop as cannabis fertilizer. No, your cannabis won’t taste like poop. And yes, it’s a good idea. But before you run out to the garden and unbutton your trousers, there are some things you’ll need to know.

If you’ve ever seen the film adaptation of Andy Weir’s The Martian, you may recall a particular scene where Mark Watney (Matt Damon) uses his erm, stools, to make fertilizer. He then uses that poop fertilizer to grow potatoes. While this made countless moviegoers somewhat queasy, it’s an entirely possible feat. Growing crops of any kind from a poop-based fertilizer is not only possible – it’s a (admittedly rather gross) recipe for success.

Why Use Poop to Grow Cannabis

Obviously, this is best suited to outdoor cultivation rather than an indoor grow room. It all starts with the soil. That’s the launchpad for any successful growth, as good, healthy soil contains the nutrients, organic matter and beneficial microbes essential to healthy and vigorous plant growth. As you near the end of your growing season, you’ll notice that the soil looks somewhat barren after harvesting your weed. For outdoor growers, post-harvest is the ideal time to throw down some top-notch organic fertilizer and reinvigorate the ground ahead of the next grow.

Acquire some manure (don’t ask, don’t tell) and mix a good amount through your topsoil after raking your beds. Alternatively, apply manure and spread it across the surface like mulch for an excellent top dressing.

How to Use Manure to Grow Cannabis

Using manure in the correct quantity has a sh*tload of benefits for you as a cannabis grower. It will help you create healthy bedding for your plants and feed and nourish them. Aside from that, you’ll encourage the kind of microbial activity you want, as beneficial bacteria will help cleanse the soil. But how much manure should you apply to the soil?

First-time users should aim for somewhere between 9 and 13kg of manure per 9 metres squared of soil area. This quantity is ideal for establishing good healthy soil beds for your marijuana plants. For future grows after that, spreading a thin layer over the top of your soil should suffice.

Which Manure Works Best For Growing Cannabis?

As you can imagine, there are a host of different animal manures you could use. You could say you’re spoiled for choice, as every living creature produces waste. But knowing which type of manure works best for cannabis cultivation will help. Interestingly, numerous options make ideal fertilizer for growing weed, and there are reasons why each of these is useful. However, a caveat is that most of these should not be used in fresh manure form. They will need to spend some time on the compost pile to allow sufficient rotting, otherwise, they could do your plants more harm than good.

Chicken Manure

Chicken manure (a great name for a band, btw) is high in the three primary nutrients we want to feed our cannabis plants – nitrogen, phosphorus, and potassium. For this reason, it’s a prime choice for use in the garden, and vegetable growers highly prize chicken manure.

However, it’s crucial to note that fresh chicken manure contains higher levels of nitrogen and ammonia that can burn and even kill plants. As such, you must use composted chicken manure – this mellows the high nitrogen levels making it safe to use. Composting chicken manure can take anywhere from six to nine months, so if you’re planning to go 100% DIY, you must plan well.

Pig Manure

Pig manure is packed with about thirteen essential nutrients, including the NPK we prize in cannabis cultivation. In addition, it contains a load of organic matter helpful in improving soil texture and quality. The downside to pig manure is that it can contain pathogens, so like chicken manure, make sure you compost it at the end of your growing season. Doing this will give it the time it needs to rot, killing off those pathogens and making it a viable fertilizer by the time you’re ready to grow again next spring.

Cow Manure/Horse Manure

We’ve lumped these together because they have similar notable qualities. They both contain some nitrogen and potassium, and both manures will be beneficial in improving the fertility of your soil. But the risk of pathogens is high in both these manure types, and they’ll require hot composting before they can be used for growing cannabis.

Another problem with using cow or horse manure is that both animals are grass-munchers. When it comes to producing fertilizer, that’s not the healthy diet you might think it to be. Many farmers use an aminopyralid herbicide to kill weeds growing on their grasslands. As cattle and horses nibble on grass, this herbicide passes through and ends up in their manure. Aminopyralid takes years to break down, and you do not want this in your soil when growing crops.

Sheep Manure

Sheep manure contains higher levels of NPK than cow manure, so it’s a better option for your plants. It also has plenty of organic matter, and that’s useful for attracting beneficial bacteria to your soil. Be sure to compost sheep manure to avoid burning or damaging your cannabis plants. That would be baaad.

Rabbit Manure

Who would’ve thought those pesky pellets could have such a wonderful use? Rabbit poo – yes, rabbit poo – is an excellent source of nutrients for fertilizing soil. This substance is superb for cannabis growers, as it’s jam-packed with nitrogen, potassium, and phosphorous – but it gets better. Rabbit manure is also loaded with magnesium, zinc, and calcium – secondary micronutrients essential to healthy plant growth.

Rabbit manure doesn’t require hot composting, meaning you can add it straight to the topsoil to deliver nutrients to your weed plants. Give the kids a shovel and send them off to collect some.

Bat Guano

Bat Guano is another example of an excellent niche manure that can greatly benefit the cannabis grower. This superb organic fertilizer is packed with nutrients that can help support plants through the vegetative and flowering stages. Bat Guano will bolster your growing medium, but only ever use Bat Guano sourced from reputable outlets. If not created under the right conditions, this product can cause problems for you and your plants.

The Main Benefits of Using Manure to Grow Cannabis

As mentioned, using manure in your soil can greatly benefit cultivators. But how does spreading manure help?

The microorganism-abundant, nutrient-rich manure proves critical structural support for your soil, which translates to vibrant, healthy, and vigorous plants. Manure offers the following advantages:

Healthier Soil Structure

Manure creates a layer of protection over the soil that, among other things, can help reduce the impact of raindrops. Rainfall can erode the soil through something known as splash erosion. This causes a loss of topsoil, which in turn can reduce crop production potential.

Improves Water-Holding

Using manure in your soil can increase the soil’s capacity for holding water. This means cultivators need to water a little less but can also reduce water stress that can otherwise interfere with plant growth.

Provides Food for Beneficial Microbes

Beneficial Microbes go a long way to help with soil health. They work as part of the overall soil environment to increase the availability of nutrients, regulate phytohormones, and increase plant tolerance to stress.

Provides Essential Nutrients

Nitrate in commercial fertilizers can dissolve into water, but this doesn’t happen with manure. The additional NPK that manure provides is precisely what cannabis plants need to thrive. Along with several other micronutrients found in manure (calcium, zinc, magnesium), these feed the plant essential ingredients crucial to its health and development.

Things to Consider When Using Manure

There are key considerations if you go down the organic route and use manure in your soil. Keep these tips in mind for safe use, and your plants will benefit.

Number One: Always check your compost for aminopyralid. Failure to do this can mean a death sentence for your cannabis plants. To test for AP, throw a half and half mix of manure and compost in a pot, water it thoroughly, and after 24 hours, add some broad bean seeds. After around three to four weeks, check back and look for cupped leaves on the sprouts, or signs of damping off. These symptoms indicate AP presence in the soil.

Number….uh….Two……: Unless you’re using rabbit manure, make sure your compost is well-rotted. Well-rotted compost is essential to avoid nutrient burn. Use wood chips, kitchen scraps, cardboard egg boxes and fallen leaves to provide vital carbon and fibre to your compost.

Using Poop to Grow Cannabis – Final Thoughts

Although using manure to grow cannabis might be offputting to some, it’s important to remember that the pros far outweigh the cons. We’ve listed the many pros above, and it’s hard to argue against the benefits of placing manure in your soil. The main downside is that it’s poop, obviously, but farmers have been using manure forever, and the results speak for themselves.

It might not be the most pleasant-smelling substance, but that won’t last. It might not be the most straightforward to acquire, but you should be able to find stockists. The main thing is the end result; if manure lends itself to producing high-quality cannabis, it’s not something to be pooh-poohed.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

Duncan Mathers