Rue is a hardy perennial with yellow blossoms and fern-like, blue-green leaves. In the past, the herb was used medicinally as an antispasmodic to treat neuromuscular problems. It is now known that medicinal uses for rue can even be dangerous and even toxic, but the plant's strong scent can repel many pests and make it a good companion plant in the garden. The rue herb is semi-woody and can be pruned. The herb can reach up to 3 feet tall. In addition to deterring smaller pests, it also deters deer from the garden.