watering time

Just a quick note: University of California guidelines recommend landscape
irrigation between 2 am and 6 am, for all the reasons mentioned previously,
including best water pressure, less loss to wind and evaporation, and in the
case of sprinklers, less time for fungal organisms to grow before foliage
dries.  An additional note about night watering has to do with the fate of
the water in the soil: since the main cause of water movement in soil is
gravity (down) or evapotranspiration (up), unused water in the evening may
actually move below the zone of most water uptake (top 18") if it isn't
being used by the plant.  Since most plants won't be as active in water
uptake in the evening as they will be in the morning, some of the applied
water may actually be wasted in the case of more shallowly rooted plants.
Now, I know that many mediterranean plants survive drought with very deep
roots, like Quercus lobata to name one prime example, but they also survive
it by having widespread roots with lots of root hairs in those top 18" to
make rapid use of any shallowly available water as well, including those
brief flash rains prevalent in med climates other than California and Chile.
For those of us without shallow water tables, very deep, infrequent watering
of large specimens may be necessary, but in that case, research shows that
time of day has very little to do with it from the plant's perspective, and
usually isn't accomplished by sprinklers.  And any oxygen that might be
carried in a sprinkler drop isn't going to get very far in the soil anyway.
Significant soil aeration isn't accomplished that way.  Over-watering too
often leads to anaerobic conditions and can be accomplished just as easily
with sprinklers as it can be with drip or a hose or a bucket.

If one has to water by hose, then getting up at 2 am isn't feasible, but
certainly 6 am would be.  

Karrie Reid

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