From the perspective of both folkloric magic and witchcraft, Alchemy Works is probably one of the best sites for your wortcunning needs. It has a wide variety of otherwise tough-to-find herbs used for a variety of purposes in witchcraft.

Botanical.com is also a fantastic resource, including providing a vast body of lore for free on the site.

And I would echo those who suggest cat yronwode's book, and Lucky Mojo in general.

For me, though, the hands-down best source for green magic and witchcraft's wortcunning is the writing of Andrew Chumbley of the Cultus Sabbati, and his Ars Philtron and Viridarium Umbris.

Nice discussion topic Ralakk, I’d like to throw a nice hawthorn thorn into the ring please.

In the UK a lot of witch bottles have been found in old buildings. These are used to bless/protect a place. I have used these in virtually all the homes I have had and have been asked to make them for other people and have taught others to make them too.

In the Museum of Witchcraft in Cornwall (well worth a visit if you are in the UK) they have a few examples of these bottles that have been found in old buildings and donated to the museum. The ones on display have Nails and urine in a bottle, a lambs heart pierced with pins in a glass jar etc. And a common one of those found is something or other pierced with hawthorn thorns.

Hawthorn in the UK has a few common names, Whitethorn, Maywitch and May (May is the month that the May tree blossoms). It is generally considered an unlucky tree and the Irish Gallic name for it means “harm”.

In many folk cultures it is believed that May is a bad/unlucky month for marriages.

The Hawthorn blossom, for many men, has the strong scent of female sexuality and was used by the Turks as an erotic symbol.

In a practical sense it is often planted as a barrier, the thorns can keep out any random trespasser, I have planted some Blackthorn (Sloe) in my garden for that reason (and so I can make sloe gin!!).

Hawthorn is often used in folk spells for purification cleansing and to enhance male potency. Due to the purification use I have made witch bottles with items inside to attract negative influences and added holly to trap them and hawthorn to purify them.

I suppose using the same theory it would be possible to attract luck into the bottle, or to draw harmony into there and then kill it. Purification can be used for both “good” and “bad” reasons. Salt purifies and cleans, but if you put too much of it in the soil it kills it, clean and sterile is not always good, so the same goes for hawthorn.