Vines have a limp, creeping growth habit with very good vigour and adapt well to different climatic conditions. Leaves are large, dull green and longitudinal with a downy underside and five moderately defined lobes. Bunches are medium/large and long with a cylindrical shape. They are sometimes winged and normally loose. Berries are medium small, noticeably oval with a blue-black thin but fairly tough skin which is thickly coated with bloom when fully ripe. The flesh is succulent with a distinctive and pleasant taste. Grapes ripen late mid-season, approximately mid-February to end March, with an average residual sugar content of 23 – 26° Balling and an average acid concentration of 5 – 7 g/ℓ.
There are a number of Shiraz clones available and selection is usually based on the specific terroir and style of wine.
Normally medium to low vigour rootstocks are used because of the strong vigour of Shiraz.
Soil, location and aspect
The main objective with Shiraz production is to establish a vineyard displaying homogenous, moderate vigour and growth. The following aspects should be considered for the production of good quality Shiraz wines:
- Cool conditions that induce slow ripening
- Proper sunlight, but not necessarily directly onto the bunches
- Relatively cool slopes with sufficient soil moisture
- Middle and higher rocky slopes facing east to north
- Rows planted in a north/south direction in cool conditions
- Rows planted in an east/west direction in warm conditions
Vine Training Systems for Shiraz
Vertical trellis with moveable wires
This is the most common type of trellising for Shiraz. The grape variety’s creeping growth habit necessitates a trellis system that supports shoots more than other cultivars.
Single Stake Trellising
This system comprises the training of each vine to a single post. It is used especially on steeper slopes with the purpose of maximizing the amount of light penetration into the canopy. The yield per hectare is optimized as the vines are planted more densely.
It facilitates the tying up of shoots required to support the vine.
This is the ideal method for cultivating Shiraz in dry land soils with lower potential because of the creeping growth habit. With the vines planted more densely the yield per hectare is maximized. More balance is created in the vine which is essential for producing quality wine.
Although this is a cheaper method of cultivating Shiraz, vines take longer to reach full production.
Irrigation and Fertilisation
Shiraz is known to be a vigorous grower and this can easily get out of hand should conditions for growth be stimulated. Fertilisation should therefore also be approached with caution and applied conservatively. It is recommended that vines are rather moderately stressed right from the very onset of the growth period instead of only during the bunch development stages and ripening period.
Pruning and Canopy Management
Shoots should ideally be positioned upright with enough leaves in the canopy to protect bunches from direct sunlight but also to allow enough diffused light through for colour and aroma development. However pruning and canopy management should be applied according to production outcome in mind. The main focus should be on balance between vegetative and reproductive growth.