A wicking bed is an agricultural irrigation system used in arid countries where water is scarce, devised by Australian inventor Colin Austin.
[1] Despite being an irrigation system (which can even be fitted with automated refill capability via rainwater tank and float-valve), it remains relatively low-tech.
This particularly benefits vegetables prone to fungal infections, such as cucumber, tomato, and squash varieties Slugs, snails, and other mollusks much prefer a moist surface.
Shrubs, trees, or anything with an invasive root structure may not benefit from being grown in a wicking bed.
Well-constructed beds with a good drain typically get flushed or diluted in heavy rain, which is not usually an issue.
A badly constructed wicking bed may even have organic matter in the reservoir layer below the water line, which can trigger the same thing.