Today is Midsummer's day, St. John's Day, one of the old quarter days of the year. Quarter days were the days when debts were settled, rents paid, that sort of thing. Christmas Day is counted as one as well as Lady's Day, March 25th, and Michaelmas, September 29th.
There is a tradition around Dundalk, Co.Louth, Ireland of lighting bonfires at the end of June, which I'm guessing might well be related to Midsummer's day, when bonfires were lit then in Ireland.
Traditionally one paid homage to fire, water and plants. So the bonfire bit makes sense. The water bit, might well be all the feicin rain we've been having lately, also good for putting out any bonfires: and the plants, well, they are benefiting from the rain, only too well!