I ended up with two, quarter-inch drainage holes in a semi-hydro pot for a number of reasons.
With one hole, a piece of LECA can effectively block it. By adding a second hole - and keeping it fairly close to the first (although I'll admit it's not part of my "QC"), The piece of LECA that blocks one hole keeps another piece from blocking the other. In reality, the blockage is fairly rare.
Add more holes, or make them bigger, and the liquid drains too fast when watering, making it difficult to fill the pot and get decent rewetting/flushing.
Add too many holes and it increases the evaporation sufficiently to defeat some of the wicking.
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