Coffee Fertiliser – the next frontier?

Reducing waste and helping create a sustainable ecological system is becoming more important in todays age where consumers and economies are looking at the holistic impact their lifestyle choices make. One of the big previously never mentioned sources of waste happens to be Australia’s most popular beverage – coffee. Each year, over 70,000 tonnes of waste coffee grounds are dumped – the majority of which going into general waste. What most people and businesses do not know however, is that coffee grounds are a nutrient dense source of organic matter which can be used to condition and improve soil.

The nutrient profile of coffee grounds are diverse in it’s benefits – the average grounds contain useful levels of nitrogen, potassium, phosphorous and magnesium. Trace amounts of copper and a base which is slightly acidic can help reverse soil degradation improving crop yields and the long term sustainability of farming.

Does this mean coffee grounds are an all benefit, no downside additive for fertiliser? Not exactly. A recent study by the University of Melbourne noted that if there is too high a percentage by volume of coffee grounds in the soil, it can inhibit plant growth by up to 20%. The key is balances. If you have too much coffee grounds, this can create phytotoxicity – creating an imbalance in nutrient levels of plants. Instead the study showed that you would want to keep coffee grounds to a maximum of 2% of density, which would then show an improvement in growth and soil quality. The added benefit is that over a longer period of time this improves soil quality without requiring the same constant levels of replenishment as normal fertilisers.

How can you do this at home? The best thing to do is integrate your existing coffee grounds waste with a home composting routine. Unless your household are all heavy coffee drinks, this should naturally keep your coffee ground ratios to a healthy level without inhibiting growth. If you’re concerned about putting too much in, you can add organic fertiliser to dilute your mixture further. Spread the fertiliser mixture on your garden beds seasonally to improve your garden yields and soil quality.

Final Tips

If you’re going to integrate coffee grounds into your soil mix, be careful with flavoured beans – some of these can have considerable additives which can change your soil pH level and lead to considerable toxicity issues. This can be a positive however – if you’re planning on working on a garden bed which isn’t going to be seeded for at least a season, you can put a high concentration of coffee beans into the bed to help rejuvenate the soil. By the end of the season the core markers for soil quality will have improved and be ready to be sown with your preferred plants.

For storage, keep your grounds in a sealed container away from moisture – due to the already wet and dense nutrient mixture, coffee grounds will often spoil through mould and mushroom growth, leeching the soil benefits.