Archimedes Plutonium writes:
In past years I have tackled dry spells with just pure watering. But
this year I am changing tactic to that of thinking that a good mulch is
even better than watering.

A wise move.

What I use is roofing tar shingles, those asphalt shingles. It

Not such a wise move. The tar in asphalt contains a cocktail of
carcinogens. Most are volatile, but I reckon there would be enough
residual in the tiles that I wouldn't want it leached into soil around
my fruit trees. Use flat rocks instead of the tiles. Not only do rocks
keep in the moisture, but they keep the soil from cooling down during the
night and this promotes plant growth. A handful of compostible material
under the rocks is advisable.

There was a scientist who achieved notority for his contribution to
greening the desert: each time he'd plant a tree he'd place a rock
alongside it. Quite apart from the beneficial moderation of moisture and
temperature extremes, but he noticed how each rock created a microhabitat
for an earthworm, and it was this earthworm that benefited the soil and
thus the tree. The worm could 'till' many metres up and down in the soil
under the rock without the risk of being cooked or dessicated when near
the surface--but trees that did not offer the protection of a nearby rock
were found to lack this symbiotic earthworm activity.
--
John Savage (my news address is not valid for email)