The resilience of yields in old vines: Part two of five of a serialized report on old vines in South Africa

By Petri de Beer

Given the historically young age distribution of South African vineyards and past experiences regarding their longevity, little attention has been paid to vines exceeding the 20-year mark. Prior to the launch of the old vine project, much of what was known about the cultivation and management of older vines was based on anecdotal evidence shared among producers.

Through years of observation and practical experience, it has been widely acknowledged that vineyard productivity undergoes a significant decline after approximately 15 years. By the twentieth year, the yield often reaches an unsustainable level, rendering the vines economically unviable. Beyond this point, the progressive onset of disease and physiological deterioration accelerates the decline, ultimately leading to severe vine degeneration. As a result, the vineyard is left in a state of disrepair, commonly referred to as a decrepit "haasbek" vineyard.

An analysis of empirical data on vineyards older than twenty years challenges the widely held assumption that vine yield declines linearly with age. In Stellenbosch, a sample of 460 vineyards was identified, while in Breedekloof, 297 vineyards were confirmed to be over twenty years old in the sample taken. Due to the diverse composition of cultivars and the evolving nature of vineyard plantings, only a select number of cultivars had a sufficient number of older vineyards to enable a comprehensive analysis on those cultivars although all cultivars showed the same results as was seen by the results of all 460 and 297 vineyards analyzed where no correlation between the vines age and its yields were found.

When accounting for cultivar variations, Chenin Blanc (62 vineyards) and Sauvignon Blanc (88 vineyards) in Stellenbosch, and Chenin Blanc (56 vineyards) and Colombar (53 vineyards) in Breedekloof were selected, vine age only showed a 10% to 26% respectively correlation of the observed variation in yield. These results confirm that this phenomenon is not cultivar specific. Moreover, the assumption that high-yielding cultivars experience premature decline due to their heavy yields is unfounded. Proper vineyard management plays a crucial role, as mismanagement can definitely lead to an early decline of vineyards.

This conclusion is supported by research conducted by Vegas et al. (2022) on Zinfandel vineyards in California, which found no negative impact of vine age on yield. In fact, under water stress conditions, older vines exhibited higher yields, likely due to their larger and better-developed root networks, which improve water and nutrient uptake.

Also similar findings were observed by Grigg (2017) on Shiraz vineyards in Australia. When controlling for variables such as cultivar type and disease presence, the research demonstrated that healthy, well-managed older vines perform equally well, or even better, than younger vines. It is theorized that one of the key advantages of older vines lies in their larger permanent wood structures, which act as nutrient reservoirs, facilitating strong vegetative growth and supporting the ripening of larger grape yields.

Collectively, these insights underscore the critical role of vineyard management and disease control in sustaining productivity across different vine ages. Instead of an inevitable decline, older vines, if properly maintained, can continue to yield optimally, leveraging their well-developed physiological characteristics to maintain high productivity over time.

Regarding the economic sustainability of South African vines older than 20 years, data from 2024 VINPRO production plan benchmarking study indicates that 53.7% of vineyards in Stellenbosch and 64% in Breedekloof were able to break even or better. This suggests that many older vines can still and are being farmed profitably. Notably, this profitability is not solely due to increased grape prices but also to maintaining yields. This is emphasized by the results from Breedekloof, one of South Africa's main irrigated vine areas focusing heavily on production and the bulk wine market, manages to sustain profitability of many older vineyards through the maintenance of good yields, without the premium value associated with old vines in the bottled wine market, where Stellenbosch plays a significantly larger role.

The significance of this data is further reinforced through its visual representation, as illustrated in (Graph 1), which provides a clear depiction of the relationship between vine age and yield in Stellenbosch Sauvignon Blanc.

However, it is essential to acknowledge the potential for survival bias when interpreting these results. While older vines can remain profitable under strict management criteria, it would be misleading to assume that all old vines inherently maintain high yields. As emphasized throughout this series, vineyard success is highly dependent on management practices. A poorly managed vineyard, regardless of age, will always yield suboptimal results. In many cases, vineyards with inherent deficiencies fail long before reaching the 20-year threshold.

Moreover, vines do not miraculously improve upon reaching 20 or 35 years of age. A young vine that produces good yields of quality fruit will produce an old vine that produces good yields of good quality fruit. Instead vine longevity and productivity are contingent upon proper cultivation, disease management, and environmental conditions. These findings highlight the need to reassess traditional assumptions regarding older vineyards and prioritize evidence-based management strategies to optimize their long-term viability.