### Clue: Miners' group is to register in spring, collecting 17 (13)
### Answer: NUMISMATOLOGY 
 ### Explanation: Definition: collecting 17
A charade of NUM (National Union of Mineworkers, 'miners' group') plus 'is' plus MATOLOGY, an envelope ('in') of 'to' plus LOG ('register') in MAY ('spring', when the darling buds appear)