Another one from Pumpkin Master, it’s not really right English to use ‘gardening’ verb in this way:
Gardening is more the general act of working in a whole garden.
Alternatives:
“I spent weeks tending it!”
“I spent weeks growing it!”
etc.
I think the technical reason is because ‘to garden’ is an intransitive verb but I’m not that hot on the terminologies of grammar, I confess I just got that reason off Wiktionary.