http://heathstreethealth.nhs.uk/services/travelling-healthcare/ Phragmites Australis, commonly known as water reed, has been used as a thatching material for thousands of years. A type of grass, it exists in wetlands around the world. Although water reed can grow to heights of over 15 feet, thatchers will usually use stems between around 4 to 8 feet long. Once harvested, the reeds are often tied into bundles approximately 8 inches in diameter for easier handling. Coveted for it’s durability and longevity, it is the obvious choice for new build properties where using the more traditional straw thatch is not essential.
http://c3patriot.com/?author=5 In England, in the past it’s use on thatched roofs was confined to areas where this plant grew naturally, such as Norfolk. However, in recent decades water reed has spread outside these areas to become relatively popular with thatchers around the UK. Internationally, water reed is the predominant thatching material, for example in the Netherlands and Germany, where little else is used.
http://lovegodlovelife.org.uk/page/33 In the areas surrounding Wimborne it is still far more common to see roofs thatched in combed wheat straw. Dorset and it’s neighbouring counties have always had a strong history of arable farming, ensuring a healthy local supply of straw for the master thatcher.