WessexGirl - the herb you want does have six letters and from what you say it looks like you have the first three letters correct. If you have a Chambers dictionary, then a quick search with your three letters should get you the word, which is an obsolete Scottish version of the 8 letter herb you have in mind (I think!) You should then be able to find the extra letters in a down clue quite easily. These do look as if they are an essential part of the clue, but can be removed and the clue still works.
If you don't have Chambers (or Bradford's Crossword Dictionary) you may well struggle to identify the herb -Googling it does not readily find it. If necessary I can tell you in which down clue to look.
Mullingar - glad you got there. Word Wizard can be very useful - tho' some purists prefer not to use on-line aids. Beware - Listener solving can become addictive! If you are going to persist and don't mind using the net, then have a look at quinapalus.com/matcher.html which provides a number of useful aids, including anagrams, misprints etc. (Real experts would know how to post that as a link!)