A wide variety of cultivars is available, but only a few are used to produce high-quality white or red wines.
Climate and soil are largely responsible for determining whether grapes can be cultivated successfully in a certain region. The climatic conditions also determine the type of grapes that can be produced in a region.
Because of its moderate winters and relatively warm, dry summers most of the winter rainfall areas in the Western Cape of South Africa (SA) are suitable for farming wine grapes.
Climatic conditions are favourable for the optimal ripening of grapes and the production of high-quality grapes for wine making. Wines produced in the Lower Orange River regions of SA’s Northern Cape are generally not the same high quality as those produced in the Western Cape. This is because of the high night-time temperatures in summer in these Lower Orange River regions.
Growing wine grapes in the summer rainfall areas is not recommended, as rain during the ripening stage will cause the berries to crack and rot.
When establishing wine grapes the following should be taken into account:
- Select an area having a relatively cold winter – this is needed for vine shoots to ripen; they need a period of dormancy to ensure good budding and fruiting in spring.
- Choose a site having fairly long days and sufficient sunlight to ripen the grapes. Sunlight is needed for good colouring of red cultivar berries.
- Avoid areas where humidity is high, or where there is a lot of fog. Such conditions are conducive to the development of fungal diseases. Excessive irrigation in low-lying areas, in addition to high humidity conditions, increases the risk.
- Avoid areas having strong winds during the growing season.
- Constant strong winds during this season will deplete the soil of water, which will affect the vines negatively.
- Gale-force winds will damage shoots and bunches of fruit. If there are strong winds when the fruit is in blossom, berry set will not be good.
- Don’t plant cultivars susceptible to sun scorch in very warm areas.
- Light intensity and sufficient ambient light during bloom and thereafter is essential to ensure good colouring for red grapes and for bud fertility.
- Avoid areas where heavy frost may occur during the budding stage (spring: late August until the end of September) or even later in the growing season. At this stage, frost can severely damage the vines.
- The terroir (climate, soil, slope, etc.) is critical for producing high-quality wine grapes and wine, and will also determine which cultivars should be planted.
- Premium cultivars such as cabernet sauvignon, chardonnay, merlot, sauvignon blanc, shiraz and viognier are recommended for cooler areas.
- High-yielding cultivars such as chenin blanc, colombar, and ruby cabernet are normally recommended for warmer regions.
- Cool southerly and westerly slopes are most suitable for establishing premium cultivars such as chardonnay, sauvignon blanc and viognier and for producing high-quality wines.
- Northern and eastern slopes are warmer than southerly and westerly ones and therefore more suitable for planting red cultivars.
- Early-maturing varieties should be planted on warmer northern slopes.
- Don’t plant vines on their own root; use certified grafted vines obtained from a nursery registered with the Vine Improvement Association.
Choose a graft combination that is most suitable for the specific soil type and soil conditions (phylloxera, nematodes, drought, wet, saline, resistance, etc) in which the vines will be planted.
For example: Richter 99 rootstock can be planted in deep fertile soils with a good water-holding capacity, while Ramsey rootstock can be planted in deep sandy soils and 101-14 Mgt rootstock in shallow soils and for earlier ripening of grapes. Rootstocks can also be used to influence vine vigour and the time of ripening.
Although grapevines have been cultivated on nearly all types of soil, vines don’t grow well in very shallow soil and soil that has a low nutrient content.
It is, therefore, necessary to establish vines on good, fertile soil with sufficient nutrients. The soil should:
- Be at least 1 m deep, or deeper
- Be well-aerated
- Have sufficient drainage
- Not be saline
- Ideally have a pH of 5.0 to 6.5 (KCl)
- Have good water-holding capacity
- Not compact easily during cultivation or contain restricted layers such as rocks.
- Not have a high clay content or shallow water table.
Sandy soils with good drainage and soils that are low in nutrients are normally warmer and therefore recommended for establishing early-ripening cultivars.
Soil volume and correct soil preparation will ensure a good root system and vegetative growth. Both the top and bottom soil should contain sufficient nutrients and organic material (humus).
PREVENT FROST DAMAGE
Take these precautions to reduce the danger of frost damage:
- Choose high-lying areas that will ensure the free off-flow of cold air.
- Plant short season cultivars.
- Use a high trellis system (for example a slanting or gable system.)
- Avoid excessive growth by applying a conservative nitrogen fertilising programme and good irrigation practices.
- Make sure soil isn’t humid and doesn’t have weeds during danger periods.
- An alarm system together with overhead irrigation can be used.
- This article was written by Danie van Schalkwyk from the SA Agricultural Research Council Infruitec-Nietvoorbij and first appeared in Farming SA.