Another herb that is present at weddings, Knotgrass is known to be symbolic of the tying together of two people. Actually, it's more literal than that. Knotgrass is used in Polyjuice potions to help temporarily turn one person's’ body in that of another. Knotgrass is native European forests, and is present in Hogwarts's Forbidden Forest. Growing from 5 cm to 4 m tall - yes a wide range! - Knotgrass has a very irregular growth pattern, perhaps due to its ability to halt the growth of animals. Besides its use in the polyjuice potion, it is also in Knotgrass mead (common at weddings) and in some love potions. Knotgrass is used by healers to treat urinary tract infections as well as fertility issues.

Knotgrass grows wherever there is a neutral level of pH level in soil (Slight acid) 6.1–6.5 to (Neutral) 6.6–7.3, and plenty of water. The more sunlight, the faster it will grow. The height knotgrass when planted in greenhouses is highly variable, anywhere between 2 inches and 14 feet! Knotgrass flowers in the summer, with the colour varying between whites, pinks, and greens. When the flowers are done blooming, the stem must be cut below the flowering. Remember: lots and lots of water.