Posted: 12/02/2014 at 08:45
There's two theories Tracey:
Water in the evening so that you lose less due to evaporation and it soaks down to the roots properly. However, the slugs and snails like the cool, dark damp conditions you create by watering in the evening
Water in the morning to avoid encouraging the marauding molluscs etc, but lose some of the water to evaporation and risk burning leaves if you get drops of water on them followed by strong sunlight (always water the soil not the plant!).