the sustainability aspects of domestic or commercial gardening: the cultivation of plants and fungi, landscaping and garden design.
The sustainability issues around domestic or commercial gardening; the cultivation of plants and fungi; landscaping and garden design.
Sustainability.SE takes gardening questions that are primarily about the sustainability aspects of gardening.
And there's a dedicated Gardening StackExchange where you can ask questions about amateur or professional gardening that are not primarily about the sustainability aspects.
For questions specifically about permaculture please use that tag.
For questions on composting use composting.