soil Why does soil dry from the outside first?

[dragon49]

I'm sure there is a scientific answer for this:

When I soak my pots, the soil first dries on the outside rims, then it gradually dries further inside, until the center is dry. What causes this pattern?

 

[geeme]

Air circulation. Air freely circulates around the outside, therefore drying the outside first. That's why you can't rely on the appearance of the soil when determining when it's time to water again. Allowing the leaves to droop just a little lets you know the inside is finally getting dry, too.

 

[Scovie]

Same effect as an ice cube melting from the outside in.

 

[Cayennemist]

Ratio of air to surface area. Evaporation occurs when there is a surplus of air, as the pot dries, the air infiltrates the soil evaporating the water.

or something like that lol
DERP my head hurts now.