Sunshine produces radiant energy that rises the ambient or air temperature significantly. In temperate and cooler climates, a site in the garden that is sheltered and benefits from the warming effect of full sun, can be used to grow plants from warmer regions that might not otherwise thrive.
Altitude also has an important effect on air temperature. At the same latitude, highland sites are cooler than lowland ones. For every 300 m increase in altitude the temperature drops by 0.5 Celsius degree (1 F). From this reason, high-altitude sites have a shorter growing season, which combined with the cooler temperatures affects the range of plants that can be grown in that area.
The temperature of the soil is important for good, healthy, root growth and affects the rate at which plants are able to absorb water and nutrients from the soil. The successful germination of seeds and development of shoots also depend on suitable soil temperatures.
The speed at which soils warms up and the temperature maintained during the year depend on soil type and the aspect of the site. For example sandy soils will warm up more quickly than clay and well-drained, fertile soils stay warm longer than the ones that are compacted or infertile. Soils from the sites with a natural, gentle incline towards the south warm up quickly in spring because they gain more benefit from the sun than the soils from a level site or north-facing ones. From this reason the south-facing grounds are ideal for early vegetable crops. North-facing slopes stay relatively cool and may be used for growing plants that require cooler conditions.
Plants become dormant to limit their exposure to winter weather, most of them heaving at least a short period of full dormancy. Woody plants start their dormancy by shedding their leaves in autumn to avoid excessive transpiration. Most herbaceous and bulbous plants dye down completely in winter and remain dormant below the ground.
The temperature of the soil and air are the most important factors involved in the onset and braking of dormancy. As a gardener it is possible to exploit this knowledge for your own interest. For example if you grow bulbous plants in pots you can awake them from dormancy and bring them into early flowering by placing them in a warm greenhouse.