In Eastern European folklore as filtered through novels and Hollywood, garlic repels vampires. Not werewolves or witches, only vampires. And you don’t even need the bulb-cloves, garlic flowers will do. (See the scene in Dracula (the novel) where the party beheads vampire-Lucy and stuffs her mouth with garlic flowers to make sure she stays dead.)
Why is that? Why garlic? And why does garlic not repel evil supernatural beings other than vampires?
Garlic aggravates the symptoms of porphyria, which is a source of a lot of the vampire myths. So it carried over. One guy with the disease reacted to a garlic pizza and a legend was born.
Or because it repels bloodsucking critters like mosquitoes. Or because vampirism resembles rabies, and rabies victims sometimes fixate on strong smells. Or because Bram Stoker knew how to add details to a story to give it an odor of realism. Sorry 'bout that.
Verismellitude?
Food? Film/literature? Off to Cafe Society. Bon apetite! 
from IMHO
Well, I don’t really know, but I don’t think the flowers smell like the cloves.
BTW, I once read that in the early Thimble Theater strips, Popeye got his strength by eating garlic. At some point that was changed to spinach. Fortunately for the olfactory sensibilities of America’s parents.
Actually, spinach, garlic, and olive [del]oyl[/del] oil makes a great combination.
Please tell me the whole post is a joke and not merely the last sentence. Our Perfect Master among others has thoroughly debunked the idea that porphyria was responsible for any vampire myths.
Cool. I recently read (but have already forgotten where) that Popeye’s spinach (previously garlic?) as a superman pill was a thinly-veiled analogue for cocaine. Sounds fishy to me but I thought I’d throw it out there.
Why not lol? it fits. The aversion to light, the red eyes, the appearance of sickly veins in the person, and the garlic thing?
Loved it. 
Not true. I’ve read all of Thimble Theater from when Popeye was introduced until Segar died. No mention of garlic. In fact, it doesn’t even mention spinach much.
In Popeye’s first Thimble Theater adventure, he got luck (not strength) by rubbing the head of the whiffle hen. The bit about spinach came along sometime later.
There was a Popeye cartoon made in 1954 called Greek Mirthology in which Popeye tries to get his nephews to eat their spinach by telling them a story about Hercules switching from garlic to spinach.
As for spinach being a veiled reference to cocaine - there’s nothing to it, nor to the rumor that it’s a reference to marijuana.
Isn’t garlic an antiseptic and a popular component in folk remedies? That seems like the most obvious source.
The hell it does
That’s more reasonable, to my thinking. Garlic is mentioned in the medical texts of Ancient Greece, Rome, Egypt, India *and *China. It’s long been believed to treat and prevent (or “ward off”) ailments of all sorts, and we know now that it does have some antimicrobial and antiparasitic qualities.
As Leonard Wolf points out, in The Annotated Dracula,
The footnote (#23 to Chapter 10) goes on to explain how garlic was used against witches and illnesses in Transylvania, and has been used as a remedy since Ancient Egypt.
Emily Gerad was the author of The Land Beyond the Forest, an important guide to Transylvania and, as far as I know, the first to draw a strong connection between vampires and Transylvania*. Stoker relied on it heavily in researching the background for his book. again, so far as I know, Stoker was the first to specify garlic as an anti-vampire talisman.** As I’ve pointed out elsewhere, Stoker presented his vampiric “facts” as genuine foklklore, but he really made many of them up himself. There’s nothing pre-Dracula about vampires not reflecting in mirrors, for instance. I suspect this is another of his fakelore inventions, and that Gerard’s mentions of the good luck, anti-witch properties ascribed to garlic in Transylvania is the reason you’re looking for.
as for the vampire-porphyria link, it’s overblown, as Barber points out in his excellent book Vampires, Burial, and Death. Some of the features used to correlate porphyria and vampires aren’t even part of the original vampire mythos, including red eyes, aversion to light (vampires were Creatures of the Night, but in literature they certainly walked around in daylight, at least until sunlight became accepted as the thing that Made Vampires Burn Up, which, despite its appearance in Nosferatu, didn’t really get :“legs” until Curt Siodmak (again! The man has shaped our monster beliefs) revived it for Son of Dracula and House of Frankenstein.
A quick perusal of Leslie Klinger’s New Annotated Dracula doesn’t add anything to this, but I’m probably missing it. This is one masive tome, and I ain’y going to search it now.
*The first asociation of vampires with Transylvania in fiction seems to be in Jules Verne’s Carpathian Castle, which predates Dracula. I suspect he got his information, directly or indirectly, from Gerard.
**He also has them use henbane, which hasn’t been remembered, for some reason. Not to be confused with wolfbane, Kurt Siodmak’s bit of anti-werewof fakelore that did make it into the public consciousness via the Universal movies.
Other bits from folklore: (mostly from “americanfolklore.net”)
Garlic was placed by the ancient Greeks on the piles of stones at cross-roads, as a supper for Hecate – a goddess of the wilderness and childbirth, or for protection from demons. The garlic was supposed to the evil spirits and cause them to lose their way. It became custom for Greek midwives to hang garlic cloves in birthing rooms to keep the evil spirits away.
The herbalist Culpepper linked garlic with the planet Mars, a fiery planet also connected with blood. According to Pliny, garlic and onions were invoked as deities by the Egyptians at the taking of oaths.
European folklore gives garlic the ability to ward off the “evil eye”. Historically, garlic has been used around the world to treat many conditions, including hypertension, infections and snakebites.
Also, the wiffle hen saved his life after being shot multiple times. I don’t remember him being all that invulnerable prior to that episode. Man, Segar could milk a plot point though- I don’t know how many days Popeye, near death, lay in the hold of the ship rubbing the hen’s head. It took a real attention span to read comics in those days 
I was amused by P. N. Elrod’s lampshading of this in the first of her Vampire Files novels, Bloodlist. The first time the protagonist, Jack, meets with someone who knows what he is, the guy has lined up as many of the anti-vampire “defenses” as he could manage on short notice, and shows Jack the crucifix and garlic he’d stashed in his desk.