I think there are a few drawbacks to this system:
1) Because you don't have water flowing through the soil, you don't get oxygen transport through the soil.
2) Because water comes from only one area, roots will naturally grow to that area, causing asymmetrical root (and tree) growth.
3) Constantly damp underground pottery sounds like an invitation for fungus or root rot.
4) All plants are on one system, so all plants get same amount of water, fertilizer, etc. Dfferent plants have different care needs.
What's wrong with a sprinkling can?
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