Fresh sweet flag plants, incorrectly termed "rushes," were periodically spread on medieval castle floors as a floor covering. These reed-like plants were inexpensive and plentiful and, when mixed with fresh herbs, were a good way to cover dirt while sweetening the air.
Sweet flag is a tall, smooth, fragrant plant that grows well in wetlands and boggy areas. In medieval times, bundles of these plants were gathered up and spread across some castle floors and the dirt floors of many medieval churches and cathedrals. Fragrant, often medicinal herbs were sprinkled among the rushes partly to sweeten aging rushes and partly to discourage bugs and molds. Fresh rushes were sometimes spread on top of the old rushes, and at other times, the entire floor was swept clean of old rushes and debris and scrubbed first. This practice served to disguise dirt and debris while insulating rooms from the cold.
In the late Medieval and early Renaissance periods, loose rushes gave way to woven or stitched rush mats on floors, which provided similar benefits but wore well and were easier to replace. By the time of the English Tudors, floor coverings in castles were mostly purchased rush mats. Carpets were used as well, but these more expensive floor coverings were often layered over rush mats for special occasions and removed for everyday use.