I collect and save rainwater for watering plants. Now the question arose
as to when to apply the rainwater. Is it best to apply the rainwater
shortly after the rain itself so as to give each tree a double dose of
water or is it better to wait for a dry spell and to water the trees
with that water.

Question: better to apply all the water at once from a rain or better to
apply smaller amounts in dryer times.

The thing I am concerned about is in a drought period, is it good to
apply water in a small region of a plant where some of the roots get
water but other parts of the tree remain sort of dry. Seems like it is
feeding some roots but other roots still in drought mode.

Archimedes Plutonium,
whole entire Universe is just one big atom where dots
of the electron-dot-cloud are galaxies