you need to air dry the petals, roses are good for this, just before the petals are about to fall carefully pick off the flower heads and remove the petal, lay them on a tray, spread them out well and leave to dry away from direct sunlight for as long as it takes really, then pack them into airtight bags. Lavender heads can be used in the same way too.I made some last year for a family wedding, but you do need to have lots of flower heads, I bought some from ebay too, they weren't very expensive, may be worth a look if you don't have enough flower heads yourself................hope it goes well......welsh