Chilli powder can hurt plants if it is used in high concentrations. However, chilli powder is generally safe to use around plants and can actually be beneficial in small amounts. Chilli powder can help to deter pests and can also add nutrients to the soil. When using chilli powder on plants, it is important to diluted it properly and only use a small amount. Too much chilli powder can damage leaves and roots, so it is best to err on the side of caution.