The flower never brought indoors
In Britain hawthorn blossom was never brought into the house: if it was, illness and death were believed to follow. In the Middle Ages its scent was said to recall the Great Plague; the explanation may be trimethylamine, which the flowers share with decaying tissue. In Ireland, meanwhile, the May bush decorated with ribbons on the first day of May was often a hawthorn.
Source: Woodland Trust, Hawthorn (Woodland Trust; National Museum of Ireland). This is a folk record, not a treatment recommendation.
Flour sprinkled on wounds: yarrow