Ne'er Cast A Clout 'Til May Be Out.
Meaning don't leave off your winter clothes until June ,as it can still be cold in May. I have always been told that this saying actually refers to the May flower not the month.
This tree is in my neighbours garden and always produces masses of blossom at this time of year. However. I think it is possibly elder blossom, so will have climb over the fence at dead of night to pick some for elderflower cordial ( perhaps not , knowing me I would fall over and not be able to get back, have to wake the neighbours for help, so NOT a good idea)