What are hardiness zones and how do they affect how you plan your gardening? Not many gardeners have come across this term before, and as such they might not be fully appreciating or utilizing this important knowledge that could really affect the growth and survival of their plants.
Geographic areas across the world are defined by something called hardiness, a factor which affects plant growth as well as the survivability of plants. Developed by the United States Department of Agriculture, hardiness zones act as a guide for anyone planning a garden bed or a crop of vegetables, to ensure that they are planting the right plants in the right places.
The hardiness zone is determined by the climate of a particular region and it is represented by a map and scale. The scale will indicate where the plant is able to thrive while withstanding the lowest minimum temperature.
Across the world, this guide has been adapted to other countries, and as such, even South Africa has a list of hardiness zones although ours are not as in depth as the US version.
Why do plant hardiness zones matter?
You might ask this question while looking out onto your beautiful garden. After all, if your plants are growing and your garden is lush, should you really care about your hardiness zone?
Having some basic knowledge about which zone you fall under can help you to improve the garden and it will also come in handy with any future garden plans.
All hardiness zones, as mentioned, are categorised according to the climate. So all zones that have a similar climate, no matter where the zone is in the world, will be placed in the same category. The categories on the scale run from 1 to 13, from cold to warm temperatures. The regions are broken down further into subcategories which are defined as either A or B.
It sounds really complicated, but when you have the map in front of you, a map that is colour coded, you can quickly pick out your zone and from there you can start planning.
The hardiness zones matter, even more so to farmers, because they will help to determine which plants to grow, when the right time is to plant them, which plants will do better in one area as opposed to another, and which plants will need a little more care.
Knowing what you can plant is important
The importance of knowing what you can plant in your zone, as it is applied to South Africa, goes well beyond ensuring that the plants you have don’t end up underperforming or dying.
When you know what you can plant, you will be saving yourself both time and money.
When planting shrubs and flowers, you will of course want to get the best out of them. But when you are planting vegetables, the importance of your hardiness zone goes beyond the beauty of the average garden.
If you live in a cold area, your usual vegetable seeds will do best when planted in the spring and summer months, but in the hotter areas of South Africa, planting and growing new plants, and vegetables in particular, in the spring and summer seasons, could potentially prevent the plants from growing optimally. Knowing your hardiness location can prevent disappointment.
Planning your garden according to South Africa’s hardiness zones
When you understand hardiness and you know your area (we’ll get to South Africa’s hardiness zones in a minute), you can plan your garden better.
This means you will have the information that will help you pay more attention to the garden layout, the time of year you plant new plants from your garden centre or start the process of growing seedlings, and if you live in an area where extreme temperatures are the norm, you can plan a way to protect your plants.
South Africa’s interior regions suffer from winter frost and summer highs that can sometimes result in heat waves of 40 degrees Celsius or more. Naturally, you might expect that in South Africa, we need plants that are weather hardy, but it’s a bit more complicated than that since South Africa has one of the most diverse climates and geographical zones on the planet.
Descriptions of South Africa’s Zones
South Africa has 5 main hardiness zones, but each with a corner or two that varies from the hardiness norms.
Zone 1: Coastal Summer Rainfall: Kwa-Zulu Natal to Port Elizabeth
The warm Indian Ocean directly influences the weather along this part of South Africa’s coastline, and as such this zone has no frost in the winter months. The southern region of this zone has winter rain and can be a lot cooler than the climate further north. The areas around Port Elizabeth are also subject to extremely windy conditions which can affect the plants.
Zone 2: Coastal Winter Rainfall: Southern Western Cape
South Africa’s notoriously windy area, where winter temperatures can occasionally drop below freezing, resulting in light frost, is actually a fantastic place to grow subtropical plants although the selection of plants that will grow well here is limited by the poor soil.
Zone 3: Winter rainfall Karoo: Worcester, Namaqualand, Karoo and Western Coastline
Although the winters can bring along light frosts, in the north of this zone and the coastal regions frost is incredibly rare. This zone has the majority of its rainfall in the winter months as a result of the constant cold fronts that batter the land and mountains, but to the east of the zone, rain mostly falls during the summer. The soil in zone 3 is highly rich in minerals and it is well suited to sub-tropical plants.
Zone 4: Summer rainfall: Karoo, Interior and Highveld
This zone is known for its winter frosts and summer heat. The amount of frost that this area is subject to can very much limit the selection of plants that can be grown here but luckily there are numerous frost resistant plants to choose from. The winter months in this zone are very dry but the summers bring lots of rain.
Zone 5: Bushveld Summer rainfall: Lowveld, Limpopo Valley, North West and the Interior of Kwa-Zulu Natal
This zone is characterised by dry but incredibly mild winters, with some frost in low lying areas and high rainfall in the summer months, although the extreme north and western regions can have limited rain. The soil here varies quite greatly but for the most part it is rich and filled with nutrients, making it perfect for all sorts of plants.
Images source: http://pza.sanbi.org/horticultural-zones