Weather: it is the combination of rain, temperature, wind sun, and air humidity that affects your garden at a given time.
Climate: it is the summary of the weather that can affect the garden throughout the year. The climate maps of your area are to be used only as a rough guide. They provide averages for many years rather than telling you the extremes of weather conditions that you will likely like (or suffer) in a given year.
In addition, the general climate of your region will be greatly modified by the factors around the garden (the local climate) and by the factors around each plant (the microclimate).
The general climate provides an approximate guide to the weather that can be expected in your garden. In Great Britain, it varies from almost subtropical (coastal areas in the south-west) to almost sub-arctic (northern Scottish highlands). The general climate is controlled by latitude, altitude, prevailing wind direction, and proximity to the sea.
The effect of latitude is evident to everyone, the southern gardens are warmer than the northern ones. The effect of being close to the sea is equally well known, the western coastal gardens are kept practically frost-free by the Gulf Stream. Less known is the effect of small increases in altitude and the harmful effect of salt plants in coastal areas for 5 miles inland.
The local climate is the modified form of the general climate. It is controlled by:
Slope: A sloping south-facing site begins its growing season about 1 week before a flat plain.
Opening: nearby trees and bushes cast shade and reduce solar energy, but also reduce the harmful effect of strong winds.
The proximity of buildings – city gardens are influenced in many ways by the proximity of walls, houses, etc. The walls cast shadows and reduce solar energy, they can also cast rain shadows and therefore reduce rainfall. The walls influence the temperature, the heat is released at night and the south-facing walls can form a solar trap.
Soil Type: Frosts are more likely to occur on sandy soils than heavy ones.
Water proximity: a large nearby lake can have a refreshing effect on hot summer days.
Microclimate: it is the modified form of the local climate in the immediate vicinity of a plant. Large variations can occur from one part of a garden to another. The walls and hedges nearby or the cantilevered plants will obviously involve less light and less rainfall compared to an open garden, the effect of this rain shadow can be to reduce the water supply to only 25% of the rainfall in the garden open.
As far as credit is concerned, the effect of the walls and neighboring plants is to reduce the risk of frost on clear and peaceful nights and to reduce the harmful effect of the wind. The general climate cannot obviously be changed. The local climate is generally impossible to change, but often they can be changed by introducing cloches or windbreaks.