Herbs

Herbs, nature provides a variety of plants with magical properties. In the series, it is first proved by Gloria in the episode The End Of The Affair when she states that she used "spells and herbs" to slow her aging down. Different herbs has different uses, in which can both aid and harm. Herbs are explored more in season 3.

Vervain

Main article: Vervain

Vervain is a popular herb that is often used in the series. The plants have been found to be toxic when touched or ingested by vampires, and when it is ingested or worn by humans, it will prevent them from being compelled by vampires. How its toxic effects toward vampires came to be dates back to the 10th century, when the Originals were first turned into vampires. Esther, the mother of the Originals, modified the immortality spell, and called on the ancient white oak tree to borrow its immortality. This spell upset nature, and so nature attempted to create a balance by making the flowers that grew at the base of the tree (vervain) toxic to these newly created beings. It also became toxic to the Originals' vampire offspring. Humans most often add vervain to perfume, tea, or coffee, as ingesting it is a lot more fool-proof than wearing it, where it can be found and taken off.

The Vervain in Elena's necklace

Wolfsbane

Main article: Wolfsbane

Wolfsbane, also known as aconite and blue rocket., has similar effects on werewolves as vervain has on vampires. First discovered in the episode Plan B, it was used to torture Mason into telling the truth about Katherine and the moonstone. Surprisingly, it's a commonly-used herb by werewolves to drink in a tea on the night of full moons, as it can help weaken themselves, so they're less likely to break free and hurt someone during their transformations. This concoction is said to taste like "battery acid" by Mason. It is still unknown why exactly wolfsbane is toxic to werewolves.

Witch Hazel

Shown in Disturbing Behavior, it was one of the needed ingredients for a voodoo ritual Gloria was using to torture information out of Stefan . Not much is known about this herb and it's potential in the series. But, in natural herblore, it's known for it's use in divination, so it could have been used for it's ability to form a connection in order to see into Stefan's mind.

Sage

Sage

Sage has a variety of magical uses in the occult world, often considered the Native American herb for cleansing and purification of the self and/or a place. It has a long rooted history in European Witchcraft as well. Sage is a plant of immortality and life, and with its properties as a purification herb, it only makes sense to use this in a mixture to extract information, such as in the Voodoo ritual explained above.

Also, in All My Children, Esther cast a privacy spell on a bundle of sage before burning it. The smoke wafted around the room, and created a soundproof barrier that would prevent any vampires or hybrids from eavesdropping on her conversations with Elena and Finn.

Diviners

First shown along with sage and witch hazel in the episode "Disturbing Behavior", the herb has been traditionally used either mixed in water or burned as an incense to bring about psychic vision. It can be assumed that Gloria used this herb to help her make a connection into Stefan's mind.

Magic Muting Herb

In the episode The Ties That Bind, Bonnie's mother, Abby, used a ground up herb to knock Bonnie unconscious. Abby later informed Bonnie that the herb had muted Bonnie's magic, and since. Abby warned her daughter to not try any spells, it could assumed that trying to do magic under the effect of this herb would be dangerous.