South Africa does not have widely recognised horticultural zones as does the United States of America. These zones are provided as a guide and exceptions do occur, e.g. isolated frost pockets in Zone 1 and frost free areas in Zones 4 and 5 do occur.
Description of zones
Zone 1: Coastal summer rainfall. Frost free: Mean monthly minimum temperature for coldest month: 5°C to 10°C
Characterized by dry, frost-free winters, this area is influenced by the warm Indian Ocean. It includes the coastal towns of KwaZulu-Natal and the Eastern Cape, as far as Port Elizabeth. The southern part is subject to winter rainfall and has cooler conditions. The coastal city of Port Elizabeth and adjacent regions are also subject to strong winds which should be taken into account when selecting plant material.
Zone 2: Coastal winter rainfall. Frost free: Mean monthly minimum temperature for coldest month: 0°C to 10°C
This region is virtually frost free, and when frost occurs it is very light and of short duration. Many subtropical plants grow well here. Close to the coast wind is stronger, especially the prevailing summer southeasterly winds. The soils are generally poor and mainly derived from the Table Mountain group (Cape Supergroup), which also limits the choice of plants in this zone.
Zone 3: Winter rainfall Karoo. Light Frost: Mean monthly minimum temperature for coldest month: -5°C to 5°C
This region is subject to light frost but in the northern and coastal regions of Namaqualand frost is absent or very light. As the name implies, this region is subject to winter rainfall, however, summer rainfall is also experienced in the eastern parts. The soils are generally rich in minerals and many subtropical plants grow well here provided that they are watered sufficiently and planted in areas where frost is light.
Zone 4: Summer rainfall Karoo /Highveld: Frost: Mean monthly minimum temperature for coldest month: <-5°C to 5°C
Situated on the "great escarpment", frost in winter is severe which drastically limits plant choice out of doors. Nevertheless there is a wide choice of frost-resistant plants which can be used very effectively. Rainfall is mainly in summer with dry winters but in the north-western area the rainfall is very low which should also be taken into account when selecting plant material.
Zone 5: Bushveld Summer rainfall. Frost: Mean monthly minimum temperature for coldest month: -5°C to 0°C
This region is characterized by its dry, mild winters, however frost may be a problem in certain areas, especially the higher lying regions. The eastern part receives a fair amount of raifall but toward the north and west it becomes drier. The soils are variable, but generally rich and the choice of plants for this region is great.
To find out more about hardiness or horticultural zones and how South Africa compares to USA and other zones, visit this link.