Garlic

Garlic is a harvestable plant in The Sims 3 and The Sims 4: Vampires. Garlic is also a known repellent for vampires.

The Sims 3
Garlic is a rare vine plant that can be harvested and bought from the grocery store.

Effects on vampires
With either The Sims 3: Late Night or The Sims 3: Supernatural installed, if a vampire eats garlic they will become nauseous, if a vampire eats too much garlic they will pass out.

The Sims 4: Vampires
Garlic is a uncommon plant that can be harvested to serve as cooking ingredients or made as decorations. Sims can get garlic seeds by ordering them from planters or on the computer.

Effect on vampires
Garlic is extremely repulsive to vampires who do not have the "Garlic Immunity" power, giving them the "Garlic Induced Irritation" +1 Uncomfortable moodlet. In it's presence vampires cannot feed on Sims or drink plasma at all. When eating it, vampires gain the "Grossed out by Garlic" +2 Uncomfortable moodlet. Vampires also see green pungent smells coming off of garlic where as human Sims see none; vampires still see it even after acquiring immunity.

Uses against vampires
Garlic is very helpful when Sims suffer from vampire invasions, as it will stop incoming vampires from drinking your Sims' plasma.

A Sim with garlic in their inventory will use it when fighting with a vampire and be more likely to win.

Garlic decorations
With Level 5 in the vampire lore skill, Sims can craft garlic decorations that they can place within their homes to ward off vampires. Sims can make Garlic Braids, Garlic Wreaths, and Garlic Garlands, all of which give the "Garlic Induced Irritation" moodlet to all vampires within the same room.

There is a lot in Forgotten Hollow called "Garliclauter Place", where one or more garlic decorations hang in each room.