In winter, very little need be done if suitable containers were used in the first place and the planting done properly. Large, heavy stone troughs, tubs, etc., should not freeze solid except under very extreme conditions. Cheaper, thin concrete and plastic containers can freeze through in certain circumstances and therefore if the plants in them are somewhat choice and if it is at all possible, they should be placed in a cool, light place – perhaps a greenhouse, light shed, or unheated room, until the cold snap is over, or the container wrapped in bubble polythene insulation material. Many very hardy subjects would not be adversely affected by some freezing, especially if the compost is kept on the dry side.
In summer, containers, even thick stone ones, can dry out very rapidly, particularly in sunny spots. Once a soil-less compost dries out it is very difficult to wet it again — the water just runs straight through, so you should always try to keep the containers adequately watered so they do not ever reach this state. Sometimes this means watering a small tub or window box in a hot or windy position two or three times a day, especially when the plants are well grown. Nothing looks worse than a half-dead tub of plants. This is why it is very important that containers placed on flat roofs should be easily accessible without a lot of palaver.
In a short time, the nutrients contained originally in the compost will become exhausted so a weekly liquid food should be given during watering between the months of April and August inclusive.
It certainly pays to instal one of the automatic watering systems now available, which save hours of maintenance time and heavy lifting. A timer can be installed so the watering is done as and when you want it, without your having to worry.