Land plants lose water through their leaves by a process called transpiration. Apart from the problem of a shortage of available water during the winter, photosynthesis in the leaves would also be difficult because there are only a few hours of very weak sunlight. Many plants therefore, overcome these problems by ‘shutting down’ almost completely.
Perennials, plants which continue growing for several years, may lose all their leaves and stems, relying on the food stored in their underground roots to get them through the winter. Annuals are plants which flower in the summer and then die off completely, leaving only their seeds to survive the winter and germinate the following spring. Some plants produce seeds which actually need to be frozen in the winter before they are ready to germinate. This ensures that they do not germinate during a spell of warm autumn weather.