Using Coffee Grounds As Cannabis Fertiliser

There's no doubt that we all want the best for our cannabis plants. From germination all the way to that first toke, the more you put in, the more you'll get out. Now, we're not saying you should douse your plants with nutrients from dusk till dawn, but there are some tricks you can use to get the best out of your cannabis plants. In fact, you could be sipping on one right now!

If you're currently enjoying a coffee, there's more you can do with those grounds than extract the juice from them. That's right; read on to find out how coffee grounds can get your weed plants into shape.

What are coffee grounds, and are they good for cannabis?

You've just made yourself a nice filter coffee, but what are the leftovers in your cafetière or machine? Well, those are your grounds—i.e. spent milled coffee beans. Now, you might be thinking of slinging these grounds into the bin. After all, you've got your drink, so you won't be needing them any longer, right? But wait! Those grounds are actually chock-full of nutrients that your cannabis plants will love. Allow us to elaborate.

The benefits of coffee grounds for cannabis plants

You might be thinking: "Why use coffee grounds when I've got plenty of fertiliser?". While a dedicated cannabis fertiliser can indeed be of great use to your plants, we'd wholeheartedly recommend that you also give coffee grounds a try. Used appropriately, the grounds can provide an array of benefits to your plants, and don't cost you more than a cup of coffee.

✅Pest control

If you're looking to keep pests at bay, whether it be slugs, snails, or other beasts, adding some coffee grounds to the soil could help to deter any nasties from making your prized plants their home. Although not proven, gardeners speculate that the pest-control prowess of coffee grounds is due to both the caffeine content and texture of the grounds.

✅Soil biodiversity

Not only set on thwarting pests, coffee grounds are also a dab hand at enhancing soil biodiversity, which is the infrastructure of bacteria, fungi, and other microorganisms that work together to help your soil, and therefore your plants, flourish. Specifically, coffee grounds release nitrogen and other nutrients, which serve to feed and sustain the beneficial microbes in the soil. Furthermore, coffee grounds can help to improve soil structure and water retention.

✅Natural pH balance

Maintaining an ideal pH level is crucial to cannabis cultivation. A pH that is too high or too low will undoubtedly cause problems, including issues with nutrient uptake. In soil, a pH range of 6–7 is required. The slight acidity helps your plants to absorb everything they need to grow healthily. While used coffee grounds aren't a fix for alkaline soils, they may have the capacity to help keep pH levels balanced.

Washed grounds are only slightly acidic (around 6.5 pH), but fit right within the ideal range for growing weed. Unused coffee grounds are more acidic, and thus may have more prowess in bringing pH levels to the acidic side. However, this claim is disputed. Ultimately, be sure to use a pH meter to ensure your soil and water/nutrient solution are both within the appropriate range.

✅Perfect for composting

Coffee grounds are a great source of organic material, and considered a form of green waste. Containing high amounts of nitrogen and other nutrients, coffee grounds are simply perfect for adding to the compost bin. As the grounds break down, they help to form soil aggregates and boost aeration and water-holding capacity, among other benefits.

How to use coffee grounds as cannabis fertiliser

So, just how can you harness the power of coffee grounds to support the health and development of your cannabis garden?

In soil

As mentioned, the primary way to utilise coffee grounds in cannabis cultivation is to apply them to the soil. Containing key macro and micro-nutrients, the grounds will support the nutritional profile of the soil. Just make sure to administer the grounds at the right time. Too early, and the roots of young plants may struggle to grow. Too late, and you’ll miss out on providing any benefits.

We recommend waiting until plants have developed at least three nodes before adding grounds to the soil. Furthermore, don’t overload the substrate; remember, you want to support biodiversity.

Though coffee grounds can be used to support general vegetation, they may also come in handy if dealing with nitrogen deficiencies or nitrogen-deficient soils; the grounds contain about 2% nitrogen by volume. The grounds alone may not be enough to fix the issue entirely, but they can help to boost nitrogen levels while maintaining an adequate pH level.

Foliar spray

If you want more of a “handheld” solution, a coffee-packed foliar spray could very well do the trick. Simply add two cups of coffee grounds to around 5 litres of water and let it rest overnight, then drain the mixture. This concoction can then be used to spray the leaves and stems of your cannabis plants, passing on the foil nutritional benefits to help them thrive.

Compared to mixing grounds into the soil, this solution is extremely mild and unlikely to cause any issues related to overfeeding. At the same time, foliar sprays are not a long-term nutritional solution, but are a good way to give plants a near-immediate source of nutrients.

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Which coffee grounds are the best for cannabis?

There's no consensus on the “best” coffee grounds for cannabis plants, though there are some types you may want to avoid (see below). Simply pop into your local coffee shop, and chances are they're dying to get rid of their used grounds. You may find yourself leaving with a free sack of fertiliser! If that's not an option, simply raid your coffee machine, cafetière, and filters to get the good stuff. Just be sure to use it as soon as possible, as coffee grounds are highly susceptible to mould if left to sit too long.

Which coffee grounds hurt marijuana plants?

While fresh coffee grounds can be used, they are more acidic compared to used grounds. So keep that in mind if you're looking to add them directly to the soil. It could shift the balance of the pH and result in an unsuitable environment for your cannabis plants.

Also, it may be tempting to use instant coffee as a substitute. However, typically this is produced using freeze-dried coffee extract and can sometimes contain additional chemicals that might have a detrimental impact on your plants.

Coffee grounds and cannabis: A useful fertiliser

Whether you're looking to save a little money on your home-growing projects or just want to try out new ways to help your plants flourish, coffee grounds could very well be the answer you're looking for. So, the next time you're emptying your coffee machine, spare a thought for those grounds and think about how they still have plenty of life in them. Keep them to the side, and you'll have a nutrient-packed fertiliser at your disposal. And trust us, your plants will love it.

Adam Parsons

Professional cannabis journalist, copywriter, and author Adam Parsons is a long-time staff member of Zamnesia. Tasked with covering a wide range of topics from CBD to psychedelics and everything in between, Adam creates blog posts, guides, and explores an ever-growing range of products.

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