I remember giving my mother a bunch of hawthorn flowers and being warned to take them out of the house as they were bad luck. I remember taking them out and planting them uselessly in the ground taking it as true because my mother told me.
This was an Irish superstition, it seems since the middle ages. Hawthorn could adorn the outdoors but to bring it into the house would signify death.
The book Under the Hawthorn Tree by Marita Conlon-McKenna, certainly has much to say about death as a book about children trying to escape the workhouse at the time of the Irish Famine. People were dying all round them and their baby sister was buried where they used to play, under the hawthorn tree.
The origin of the link with death associated with the hawthorn, it seems began when it was said that the flowers smelled like the plague. In later years, according to Trees for Life, botanists discovered that the hawthorn flower has the chemical trimethylamine which is also a chemical made by decaying flesh. This was a smell people were used to when copses were kept in the house for days before burial and makes sense of the link made between hawthorn and death.
So although I like the blossom of the hawthorn, it won't be adorning the rooms of my house. Not because of any superstition or bad luck, but because I just don't happen to like the smell of rotting flesh, even from a flower.