Spent Coffee Grounds

Spent coffee grounds (SCG) are the solid residue left over after brewing coffee, containing roughly 50% of the original caffeine and a significant amount of organic compounds, including nitrogen, potassium, and magnesium. While traditionally considered waste and sent to landfills—where they produce methane and carbon dioxide—they are a valuable, nutrient-rich resource for home and industrial use. 

 

 

• Gardening: They are a nitrogen-rich "green" material for compost. They can be used as a soil amendment to improve structure, water retention, and aeration. They are often used to attract earthworms.
• Pest Control: The texture and caffeine content can help deter pests like slugs, snails, and ants.
• Household Odour Removal: Dried grounds act as a deodorizer in refrigerators, freezers, or to remove smells from hands.
• Cleaning: The abrasive texture is effective for scrubbing pots, pans, and grills.
• Skin Care: Used in DIY body scrubs to exfoliate skin.
• Growing Mushrooms: They serve as an excellent, pre-pasteurized substrate for growing mushrooms, such as oyster mushrooms.
• Industrial/Other: They are being researched for biodiesel production, biochar, concrete additives, and as a natural dye for fabrics.

Tips for Use

• Avoid Overuse: When adding to soil, do not exceed 15-20% of the total soil volume, as they can clump and hinder water penetration.
• Composting: It is best to compost them before direct application to break down any remaining caffeine and potential pathogens.
• Safety: While generally safe for plants, they can be toxic to dogs if consumed in large quantities.
• Storage: They should be used within a day or two of brewing to avoid mould, or stored in the fridge/freezer.

Acidity Levels
Contrary to common belief, while fresh grounds are acidic, used coffee grounds generally have a near-neutral pH (approx. 6.5 - 6.8), making them suitable for most plants.