Possible Clues:

• Start of summer or winter
• Longest or shortest day
• Breaking up soils, etc., comes at a turning point in the summer
• Summer or winter starter
• On this day, the long and the short of it is, Spanish sun hits road with frost
• People go to Slane to see it in various soils, etc.
• The longest or shortest day
• Time of longest or shortest day
• The shortest or longest day of the year
• Semi-annual occurrence that begins 28- and 35-Down