Winter has come
We have been blessed with an unusually cold winter this year, and the majestic Stellenbosch mountains have been capped with snow for quite a few days now. Above average rainfall (298 mm in the winter months) has filled up our dam and saturated the vineyard’s soils. The vines are sleeping and not a leaf is visible. Like skeletons of their summer growth, they lie and wait for the warmer temperatures of spring to bud and start their process of rebirth.
It’s a less manic time of the year in the vineyard, but there are still crucial tasks at hand.
Winter task 1: Cover crops
Sowing a cover crop keeps weeds at bay, fixes nitrogen into the soil so less fertiliser is needed, creates diversity for beneficial insects and soil organisms, and aids drainage, avoiding soil compaction.
Winter weed control ensures that the inter-rows are free of weeds when the vines bud; thus, the vines have no competition, can grow strongly and are able to ripen the fruit optimally.
Winter task 2: Pruning
Winter is also the time when we prune and train the vines.
There are several considerations when we prune; each is intertwined to cover vine health, harvest factors and budbreak relative to spring frost and cold fronts. These are the main considerations:
1. The 3-year period
One thing about grapes that differs from most other fruit is that the grape clusters for the current year’s fruit were formed in the canes in late spring of the previous year. So when we prune, we have to keep in mind not just this year, but what occurred last year and what we want to see next year.
2. Vine health
In order to determine the health of a vine, we look at its dormant state. If it shows healthy growth and sturdy canes then we consider that vine to be in good shape. If it is weak and stunted, we need to prune more aggressively to remove wood and allow the vine to concentrate energy on a more limited scale.
3. Ratio between fruit yield and leaf area
Based on the demonstrated health of the vine, we prune to achieve the desired ratio of fruit yield for the expected leaf area. Adjustments to the total yield are best made at pruning time. The grower can extrapolate yield based on:
- The expected weight of a normal cluster, with two clusters deriving from each shoot
- The number of buds selected to create those shoots on each vine
- The number of vines per acre.
4. Balance and timing
One size does not fit all: a weak vine will be pruned differently than a healthy vine. And this ties in with harvest considerations.
Besides the expected yield at harvest, another concern is harvest timing – there is a real time continuum here. Pruning influences the emergence of new growth, or budbreak. The timing of budbreak influences flowering and set, which influences timing of colouring (or veraison), which is connected to the timing of ripeness and harvest. Note that there are many other things influencing this timeline, including grape variety, clone, rootstock and, not least of all, the weather.
But, if we prune 7 ha of Pinotage in the same geographic area, all in one week, we’d expect much of it to be ready to pick at the same time. In cases like these, we often try to spread pruning out over the month to help extend the harvest time ever so slightly. This helps with fermentation space management in the cellar.
5. Vine longevity
To ensure that our vines live as long as possible, we follow best practices to avoid the spread of any viruses or pathogens that can shorten the life span of the vineyard.
- We control virus-spreading vectors like mealybug by creating conditions for their natural predators to thrive; this is known as biological control. Infected vines are removed, root and all, to avoid further spreading.
- Young vines are pruned first and shears then sterilied to ensure that there is no spreading of harmful pathogens from old infected blocks.
- We also spray the vines with a natural biological fungus (Trichoderma). This outcompetes other harmful funguses that cause rot in the vine, slowly killing them off. Special pruning practices are also applied to ensure that these bad funguses aren’t given a chance to take hold and cause any rot or dieback.