In article , david@abacus-
nurseries.co.uk says...

On 03/06/2014 22:32, Roger Tonkin wrote:
I have an automatic watering system for the greenhouse. It is
fairly basic and allows me to water once or twice a day at two
different times.

Last year I watered for an hour in the evening (7.00pm), this
year I'm doing half an hour am (6.00am) and half an hour in the
evening (6.00pm).

What do others do? Which is best?


I presume it is linked to some form of drip/trickle irrigation system.
I'd have thought that the thing you really want to know isn't how long
to leave it on for but how much water each plant is getting.
If you have individual pipes to each plant/pot then put one into a
bucket and see how much water you get in half an hour.
The problem with this sort of system comes when you grow a range of
plants with different requirements.

As it is watering just tomatoes, and they are in the soil, not
pots or grow bags, I think that it is probably impossible to
over water (famous last words?).

I was interested in the timing because of the possibility of
occasionally not being able to open the greenhouse so that it
might get very hot and dry out the soil. Would a morning
soaking last 24 hrs in that situation, or would an evening
soaking give the plants an opportunity to recover for the next
day?

--
Roger T

700 ft up in Mid-Wales