Haarlem with Bleaching Grounds
Linen was the main textile fiber European and UK for household and personal textiles at the period shown in the painting. Thus it was linens that were being sun bleached,not cotton. Indeed all over Europe wherever linen was produced be it at home or in a textile factory it would be whitened by laying rolling long widths of fabric out on grassy fields.
From growing linen to the sun/grass bleaching of it there was and or still is something special about the Holland/ Netherlands. Again though linen was grown all over Europe and the UK some of the finest came from that region. Even when grown elsewhere royal, wealthy and or textile manufacturers sent their linen to the area for the treatment. Ireland was another place famous for it's linen and bleaching of it via sun/grass.
Problem with bleaching fields is they took up lots of land that otherwise could be put into production for farming,livestock, or housing. As the population of European cities and towns grew it became more difficult to find clean/pristine areas to use soley for bleaching fields. The things require land that is not only free of trees/bushes, but obviously not recently used by livestock or horses (you can't or rather wouldnt want freshly washed linen dried over cow pats), and had to be kept free of same whilst the linen was laid out.
Linen also was highly valuable in those days, especially the richly embroidered and fine linens of the wealthy; hence prone to theft. Linen laid about on fields was obviously easy pickings for theft or simply confiscated by armies. In several famous European battles either things were held up whilst the linen was gathered up before the approaching army trampled all over it, and or the same was confiscated as war loot and taken away.
In order to sun bleach linen you need grass, or bush to lay things upon but also the items must be kept wet until the desired level of whitness is reached. In the era before hoses and such one or perhaps a small army of workers would have to go up and down the field with waterng cans at regular intervals to keep the linen moist. Or depending upon the climate/time of the year things simply left out during "light" showers followed by clear weather.
Cotton in Europe:
Cotton had been known in much of Europe since at least the Crusades or even before when it was brought back from Egypt. However given the small amounts imported it was very expensive thus only the very wealthy had any of the stuff. OTHO flax, hemp, and nettle were grown all over the UK/EU with many farming or other families with land setting aside plots or two for the sole purpose of growing the plants. This linen and hemp would be used to make threads and textiles for the family up to and including whatever linens would become part of female's dowry.
For some odd reason it never occured to Europeans then to grow cotton elsewhere and import the fiber back home for processing. This slowly began to change as England, France and the other great European powers aquired colonies in the Caribbean and North America. Things really began to take off when the United States, a new country with vast land and other resources begain growing cotton. As elsewhere in the New World having cheap slave labour made working vast plantations "easy" for their owners,who in turn became quite wealthy as indeed did the countries in question.
Once the Industrial Revolution took hold in the UK and many EU countries it became easy to mass produce tons of inexpensive cotton threads and textiles. This began the slow decline of linen as the preferred textile and all that sun bleaching. For one thing unlike flax, cotton can be chlorine/chemically bleached with more margin for error before you destroy the fibers.
The other thing that killed bleaching fields was the invention of Persil with it's perborate bleach. Now housewives/laundries could simply boil linens white in <30mins rather than a day or longer of laying things about in the sun. Moreover this bleaching could be done regardless of the weather. All they had to worry about was finding ways to get things dry on a less than perfect day.
