To water a newly planted tree you should soak the area around the tree really good with a hose until the water starts running off.
When watering the newly planted tree apply 1-1.5 gallons per inch of stem caliper at each watering.
When watering newly planted shrubs, apply a volume of water that is 1/4 - 1/3 of the volume of the container that the shrub was purchased in.
A tree gets water through it's roots from the ground.
As a tree grows so do the roots of the tree and the roots of the tree can extend deep into the ground and even reach ground water sources.
When the rain soaks the ground the tree soaks up some of that water and whatever the tree does not soak up the rest of the water then soaks into the ground.
The tree can then soak up that other water when needed.
Trees absorb water through their roots.
Most of the water a tree uses enters through the underground roots.
Tree roots are covered in tiny hairs with beneficial fungi growing on them that draw water into the roots by osmosis.
The majority of the roots that absorb water are in the top few feet of soil.
In conclusion, trees have placed themselves in the cycle that circulates water from the soil to clouds and back.
They are able to maintain water in the liquid phase up to their total height by maintaining a column of water in small hollow tubes using root pressure, capillary action and the cohesive force of water.
Trees draw water from the ground through the process of capillary action.
The phenomena of rise or fall of liquid in a capillary tube is called capillary action.
Plants have very narrow tubes which travel from the roots to its tallest parts.