Coffee grounds can benefit plants and flowers by improving soil health, but they must be used carefully. According to Linda Brewer, a soil scientist at Oregon State University, coffee grounds add carbon and bulk to soil, which supports beneficial soil bacteria essential for plant growth. However, coffee grounds are low in key nutrients like nitrogen, potassium, and phosphorus, so they cannot replace compost or fertilizer.
A thin layer of no more than half an inch of coffee grounds sprinkled on garden soil can enhance soil structure and drainage, helping moisture-loving flowers such as bleeding heart, hosta, and primrose thrive. Coffee grounds also improve water retention and aeration, which benefits plant roots. However, they should be kept away from plant stems to avoid potential harm.
Overusing coffee grounds can be detrimental. Excessive amounts may harm beneficial insects and soil microbes, including earthworms, because caffeine acts as a natural pesticide. While coffee grounds can deter slugs and snails, too much can disrupt the soil ecosystem and negatively affect plant health.
The best practice is to compost coffee grounds with kitchen and yard waste, allowing them to break down and release nutrients gradually. Composting also supports a diverse microbial community that plants rely on. If composting is not an option, gardeners can sprinkle coffee grounds sparingly around plants to give flowers a gentle nutrient boost without overwhelming the soil.
In summary, coffee grounds can be a helpful soil amendment for flowers and plants when applied in moderation, improving soil texture and supporting healthy growth without replacing traditional fertilizers.
