During the summer, plants that are potted in planters, troughs or urns should be watered during the morning between 6am – 10am before the heat of the day sets in. This will ensure any water does not evaporate before your plants and the soil has had chance to drink it. The early evening is also a good time to water your potted plants, as this will also any excess water to evaporate before nightfall.
Another reason to avoid watering potted plants during the heat of the day is to avoid your stone planters from cracking. Splashing cold water onto hot stone can cause cracking, however this is very rare, and stone remains the most durable and long-lasting material for planters as permanent outdoor fixtures.