Mint is fairly tough, but it can attract aphids, spider mites and whiteflies, especially when the plant is stressed. Look under the leaves for tiny insects or fine webbing, and wash them off with a strong jet of water, or use neem oil or an insecticidal soap. Keep the plant well-ventilated, and don’t crowd it. In colder regions, where mint dies back in winter, cut it down and mulch it. It also helps to root a few cuttings in water as a backup.