Drying foliage/flowers for arrangements

I know that probably none of you do this - me neither until recently but Ive been asked by the local school to do a xmas wreath making class. Obviously I agreed straigh away
OMG - its not even October and Im already having slepless nights about foliage. I
have a hedgerow of amazing rosehips - i searched loads last night but couldn't find anythinh - is there a way to preserve these?

Any ideas on foliage I could gather now that would look good in December would be appreciated.