Autumn in Napa Valley is a glorious time. It is beautiful to watch the vines as they begin to lose their leaves and enter their winter dormancy as we hope for the rains to come replenish the soil moisture and return the lovely green grasses to the hillsides.
After all of the hard work throughout the year, the Napa Valley grapegrowers are able to take a moment in the fall to reflect on the 2015 vintage. During this time, it is important to think both about the successes and the challenges of the year, to understand how the season will ultimately affect the wines produced, as each wine is a reflection of an individual site and unique vintage. It is also a great time to plan for the coming year.
The reality is that, although the 2015 harvest is over, there is still plenty of work to be done in the vineyard in preparation for the winter. Fortunately, many vineyard workers in Napa are employed year-round and are prepared to take on these important vineyard tasks prior to the start of winter pruning.
An early harvest, like 2015, allows growers more time to give the vines nourishment and replenishment before dormancy, which promotes building deeper and more complex root systems and enhancing the uptake of nutrients for storage over the winter. Meanwhile, the grapevines are still at work preparing for rest, by storing carbohydrates and mineral nutrients needed during the dormant period to aid in fueling new growth for the next season.
In this way, the period post-harvest is a critical time for the vines to get water and fertilization to ensure a timely spring growth. Luckily, this year we have already received some well-timed rains that have aided in limiting the amount of irrigation water used and helped to incorporate compost into our soils.
Compost additions are not only important for delivering nutrients that aid in the growth of the vines, but also positively contribute to the health of the soil. By adding compost, we are increasing the organic matter of the soil, thus improving the soil structure and its ability to retain water — all of which will lessen soil erosion.
Staying ahead of El Nino
Growers are also taking time this year to prepare for what climatologists and weather analysts are forecasting to be an El Nino winter, which may bring some much-needed rains to Napa Valley, but can also present challenges to preventing erosion and maintaining soil stability. Winterizing vineyards is an important, multifaceted process that includes seeding cover crop, spreading straw and stabilizing hillsides, and cleaning drainage systems and drop-inlets. It requires significant forethought on the part of growers.
First, there are many types of cover crops planted. Perennial crops such as grasses are important to include in the winterization process to help mitigate soil erosion. In areas that are more prone to water runoff and soil erosion, such as sloped or hillside vineyards, grass cover crops will not need to be replanted yearly, but can be made more permanent.
In the case of recently tilled soil, or in areas where cover crop cannot be seeded, it is beneficial to spread straw to create a barrier between the disturbed soil and early rain. To help prevent or direct the flow of water and to stop soil runoff from reaching our drainage system and eventually our waterways, many growers also put out straw wattles, sometimes referred to as “straw worms,” which consist simply of straw compressed in cylindrical netting.
Finally vineyard drains, ditches and drop-inlets are being cleaned out to prevent water backups and flooding of vineyards due to rains.
Even as grapegrowers are taking steps toward winter preparedness and erosion prevention, water conservation and the drought are still at the forefront of everyone’s minds. In fact, the two issues go hand-in-hand. The work being done now sets the stage for healthy soils, high in nutrients and organic matter, which in turn helps improve water infiltration and retention during the wet months; it also improves overall vine health, while reducing the amount of water needed during the dry season.
So, let’s hope for a wet winter and a healthy start to the 2016 vintage!