>Thatch is popular in the United Kingdom, Germany, the Netherlands, Denmark, parts of France, Sicily, Belgium and Ireland. There are more than 60,000 thatched roofs in the United Kingdom and over 150,000 in the Netherlands.[11][citation needed] Good quality straw thatch can last for more than 50 years when applied by a skilled thatcher. Traditionally, a new layer of straw was simply applied over the weathered surface, and this "spar coating" tradition has created accumulations of thatch over 7’ (2.1 m) thick on very old buildings. The straw is bundled into "yelms" before it is taken up to the roof and then is attached using staples, known as "spars", made from twisted hazel sticks. Over 250 roofs in Southern England have base coats of thatch that were applied over 500 years ago, providing direct evidence of the types of materials that were used for thatching in the medieval period.[6][page needed] Almost all of these roofs are thatched with wheat, rye, or a "maslin" mixture of both. Medieval wheat grew to almost 6 feet (1.8 m) tall in very poor soils and produced durable straw for the roof and grain for baking bread.[citation needed]
>Technological change in the farming industry significantly affected the popularity of thatching. The availability of good quality thatching straw declined in England after the introduction of the combine harvester in the late 1930s and 1940s, and the release of short-stemmed wheat varieties. Increasing use of nitrogen fertiliser in the 1960s–70s also weakened straw and reduced its longevity. Since the 1980s, however, there has been a big increase in straw quality as specialist growers have returned to growing older, tall-stemmed, "heritage" varieties of wheat such as Squareheads Master (1880), N59 (1959), Rampton Rivet (1937), Victor (1910) and April Bearded (early 1800s) in low input/organic conditions.[12]
>In the UK it is illegal under the Plant Variety and Seeds Act 1964 (with many amendments) for an individual or organisation to give, trade or sell seed of an older variety of wheat (or any other agricultural crop) to a third party for growing purposes, subject to a significant fine.[13] Because of this legislation, thatchers in the UK can no longer obtain top quality thatching straw grown from traditional, tall-stemmed varieties of wheat.