Probably, if it's wet enough. Still probably won't work as well cause they tend to dry out fast

Gravel won't, but concrete might.

I'm sorry; but no. (Well, to an extent.)

A wick has to be able to absorb water. The process that is happening; is that, the wick is tricking the water into believing that the pot is deeper, and there is more soil to be saturated before the water begins to perch.

Rob

I would say the gravel might a bit, but not enough. Concrete...no. Concrete would act similar to the bottom of a pot. I'm not an expert on gro-bags, so take MHO with a grain of salt.

You're getting a diversity of opinions here! :) A wick has to be able to pull water from the potting mix, and gravel just won't do that. That's why placing gravel in the bottom of pots in order to improve drainage is a fallacy (if you don't understand this, read the latest incarnation of tapla's water movement in containers thread). I suggested that concrete might because concrete will, in fact, absorb water. Whether it will or not, though, is beyond my scope of knowledge.

Wicking or Capillary Rise is due to water attracted to particles climbing upward as film of water, along with the cohesive force dragging more water along with it to thicken the film of water. The height will depend on the total holding force against the total weight of the column of water( Gravitational Potential Energy) or the amount of energy to lift a substance a certain vertical distance. The PWT is caused by the same principle. Fabric Pots should wick from any moist substance with a good capillary contact. The Efficiency and Rate depending on the matching of the textures of the materials. I seen Fabric pots wick from free water, sand beds, or other sources that are not too fine textured to resist upward rise in to the fabric.

Addition: Concrete and Cinder Block with wick water to a limited degree. I see spreading capillary circular water patterns on the patio surface under the containers.The Oil Stains on Concrete Driveways is from the absorption of liquids. Water evaporates quickly, so are not noticed. The more circular the drainage pattern, the more capillary forces are dominating than gravitational forces.

Ernie, I don't think concrete absorbs water, rather lack of solid sides of the pot would allow the concrete to wick the water to the side...but I could be mistaken. I'll have to re-read CS-WM&R.

Concrete doesn't act as a wick. Excess water will run out of the pot; and across the concrete the same as it would if the pot were elevated with no contact. once the gravitational pull no longer over powers the waters adhesion to the soil particles, and cohesion to itself inside the pot, the water will cease to drain.

(The water's adhesion to the concrete plus gravity; may slightly increase drainage, but not significantly.)

Rob

EDIT - You could take a large towel, fold it 4-5 times, and place it under the pot. That would act as a wick.