Last in the "ZOMG RUSHES" series. (Or maybe next-to-last; see closing paragraph below.)
I found an 1891 book by one Alfred Burton titled "Rush-bearing: an account of the old custom of strewing rushes; carrying rushes to church; the rush-cart; garlands in churches; morris dancers; the wakes; the rush." (Because why make the reader wait til the table of contents to tell them everything that's inside?)
Much like my research into maypoles, it seems that there is some evidence for rush-strewing before Elizabeth; then a whole lot of it starting in the late 1500s and into the 1600s. There was one reference a whole lot closer to my period of interest than I'd expected to find:
William the Conqueror granted certain lands at Aylesbury to one of his followers on condition of ' Finding straw for the bed of our lord the king, and to straw his chamber, and by paying three eels to our lord the king when he should come to Aylesbury in winter. And also finding for the king, when he should come to Aylesbury in summer, straw for his bed, and, moreover, grass or rushes to strew his chamber, and also paying two green geese; and these services aforesaid he was to perform thrice a year, if the king should happen to come three times to Aylesbury, and not oftener.'
This referenced one "Blount, 'Tenures of Land, 1679." Guess what? That's on the Web, too. It seems to be a sort of curiosity book, listing all the odd and strange things that kings decided their landholders had to provide to them. "Herbam ad juncandam" - yep, that's grass and rushes. Only thing is... the footnote in the 1815 reprint of Blount, on page 12, has this as "Plac. Coron. de 14 Edw. 1" These "Plac. Coron." notes are at the end of many of the reprinted law texts and I'm thinking that it means that the decree was issued in the 14th year of the reign of Edward 1. So... not William the Bastard and 1066 at all.
The next citation Burton brings to bear is from 1207, much later than the Anglo-Saxon period
BUT ANYWAY for later period, he does call out many references to 'strewing the rushes' and 'green rushes' and such, and it becomes hard to imagine that mats are being referred to. By Shakespeare's time, putting down new green rushes was a sign of hospitality for guests, and sarcastic comments indicated some folks would do this for strangers but old friends merited not a single rush. Street-sellers hawked "green rushes, o!" and laws were passed as early as the 1400s controlling where and how punts full of rushes could unload at the London docks. It all seems to make more sense if we are considering loose rushes, easier to harvest (and still green!) and more disposable, than rush mats which would require more work, be more expensive and would hang around. Rushes in the summer are used interchangably with straw in the winter in some citations, further suggesting a loose toss of plant matter.
What of the Duke du Berry's book of days from yesterday? Even if "strewn rushes" in England refers to loose plants, it doesn't preclude straw or rush mats from being used elsewhere, or by particular houses. Especially rich ones. Large mats, like the one shown in the picture, would take significant labor to accomplish. The Sherington site estimated that it would take a week of sewing to make a 12' x 12' mat - on top of the time it took to braid up the rushes.
So do I strew rushes or not? It would seem that the custom isn't documented earlier than 1207 by what I've read so far. I am somewhat curious to see what a rush-covered surface is like to walk on... but harvesting, transporting and then removing the rushes would be a hassle. I'll think on it.