Every spring, tulip farms in the Netherlands paint the landscape with bold colours.

The country is known for its flowers. Two-thirds of the world's cut flowers were grown in the Netherlands in 2005, worth $US4.2 billion, according to the US Department of Agriculture.Red, pink, yellow and purple are favourites among the Dutch and tourists.

The area around Lisse, in west central Netherlands, is now covered in fields of tulips. They are grown primarily for bulbs, but some gardens are of the pick-your-own variety.Keukenhof, a 32-hectare park in Lisse, is probably the most popular tulip garden in the Netherlands, where 7 million tulip bulbs are planted each year. The best time to see the tulips is in April and the beginning of May.

The tulip craze has spread across the world, too. Germany also cultivates tulips for the bulbs. At Degenhardt-Sellmann Spezialkulturen in Schwaneberg, Germany, about 40 hectares of tulips are grown. Turkey, India and China all boast similar festivals at pick-your-own farms.

Despite the obvious beauty, large-scale flower cultivation has a downside, especially in the Netherlands - fertiliser run-off that infiltrates the ground water and oceans. A recent European Union directive attempted to limit the amount of nitrates used in agriculture and, although the amount of fertiliser decreased in the surrounding waters, the Netherlands was unable to meet its goal.