Wicking Pots vs Sub-Irrigated Reservoir Pots

What each one actually does

Wicking. A physical wick bridges the reservoir and the soil. Water climbs the wick by capillary action and moves into the mix where the mix is drier than the wick. The reservoir and the root zone are physically separated, so there is no route for roots to grow down into standing water. The rate is limited by the wick, which is a feature: it is nearly impossible to over-supply a plant this way.

Sub-irrigation. The media sits on a perforated platform, or on a layer of inert granulate, directly above the water. Capillary rise happens through the media itself. This moves considerably more water than a wick, which is why the large edible boxes all use it, and it depends entirely on the mix being open enough to wick.

How to tell which one you bought

Lift the plant out, or look down the fill tube. If you can see a rope, a felt tail or a fabric tab hanging into the water, it is a wick. If you see a perforated plastic platform, an aeration screen or a layer of coarse mineral granulate sitting directly over the reservoir, it is sub-irrigation. Some designs use both - a granulate layer with a wick to start the column - and those behave like sub-irrigation once running.

Which fails, and how you would know

Both fail silently, which is the genuine argument against this whole category and one nobody makes. A wick that has mineralized in hard water or been colonized by fine roots stops moving water while the reservoir stays visibly full. A compacted mix in a sub-irrigated box does the same. In both cases the water-level indicator says everything is fine and the plant is drying out.

The practical defense is to check the soil, not the gauge. Push a finger or a probe into the upper half of the mix once a month. If the reservoir is full and the mix is dry, the transport path has failed - lift the plant, rinse the wick or loosen the mix, and prime it again from the top.

Which to choose

For a houseplant on a shelf, a wick is more forgiving and harder to get wrong. For anything with real water demand - a floor plant, a tomato box - the wick becomes the bottleneck and sub-irrigation is the right mechanism. And if your mix is heavy, or you are inclined to use garden soil, choose the wick, because sub-irrigation simply will not work with it.

Either way, the mechanism matters less than the reservoir size. The published-capacity table is a better basis for a decision than the plumbing, and the full mechanism explainer covers the physics if you want it.