This is an excerpt from my research into high medieval English pastry. For more information and a full bibliography, see “Raising a Coffin” and “Crustardes of Flessh” on the Files page.
One potential source of information on medieval cereal crops is blackened roof thatch from standing medieval buildings. Layers of soot-blackened thatch survive on some medieval English buildings dating from the medieval period (specifically the 14th and 15th centuries) and John Letts (see sources) has examined over 200 samples, all originating from the South of England and most coming from Devon. (Typically roofs in the north of England were thatched with water reed or sedge [Ambrose and Letch].) These samples have preserved not only grain-bearing plants (with both the ears and straw intact), but also crop weeds and other vegetables. These roof samples provide us with a glimpse into complete medieval fields, and allow us to see how crops changed over time. The most significant finding is the diversity of crops within a medieval field:
Most samples contain ‘land race’ mixtures of bread wheat (Triticum aestivum), English rivet wheat (Triticum turgidum) and rye (Secale cereale) which grew to 6ft (1.8m) or more in height – far taller than modern varieties – as well as barley (Hordeam vulgare) and oats (Avena spp). Land races evolve over many centuries when crops are grown in heterogeneous conditions, year after year, from seed saved from the previous year’s crop. The result is that every plant in a land race is slightly different from its neighbour, and medieval cereals were consequently very uneven in straw height, ripening time, grain yield and other agronomic traits. This diversity ensured that a portion of the crop almost always set seed irrespective of the many environmental stresses that can destroy a crop such as drought, waterlogging, frost or crop disease. (Letts)