Rain water is the purest water than can be applied to the vines. Irrigation water is typically of low quality and high salinity, adding salts to the root zone. This free, clean water helps the vineyards that rely on drip irrigation to cut back on water usage, and provides much-needed water to the vineyards that dry farm.
Arid climates like California tend to have soils with high salinity and, much like human beings drinking seawater, vines can become dehydrated from salty soil. When salt levels get too high in vines, it can cause ‘leaf burn’ or browning. Rainfall benefits the vineyard by pushing the salt through the soil, allowing the vines to take up more water and absorb more nutrients.
A wet winter can also help condition the vines and assist in a more traditional cycle of grape growth. When a season of warmer weather arrives in the vineyard after a wet winter, it can help the vine transition naturally to growth and bud break. A warm, dry winter runs the risk of early bud break, and if it is followed by a cool, wet spring there is a risk that frost will damage the crop.
Winter rains are great for the soil and vines, but there is the risk of runoff and erosion if the rain falls at a high rate per hour, which can remove the top soil around the vines where cover crops aren’t grown. Alternatively, if the rain stays stagnant and drenches the soil too much, it can ‘drown’ vines that are not on well-drained soil. Rainfall can also cause soil compaction, which can have an adverse effect on vineyard production by reducing oxygen levels in the soil and making root growth more difficult.
That said, rain during winter has more potential to be beneficial than other times in the year. Prolonged damp conditions can lead to mold, mildew, and other diseases in any season, however there are additional concerns during the spring and fall.
Grapes are formed from flowers, and heavy rain can reduce crop sizes by knocking the blooms off of the plant in the spring. Grapes also need sunlight in order to ripen, and rain and a thick blanket of fog can delay harvest if the vines aren’t able to effectively photosynthesize. When rain falls on mature, fruit-bearing vines, the fruit takes up water, which can dilute flavor and throw off the sugar/acid balance, and if there is too much rain, the grapes may start to swell and split, which can cause spoilage and the increase the danger of mold and mildew.
Our vineyard is on a drip irrigation system and is monitored through in-soil sensors that measure the exact deficit of each vine so that no water is given unless necessary, and this rainfall allows us to extend the time between watering.
Like so many arid climates, our soils also contain a decent amount of salinity, and this rain has washed away the build-up, allowing the vines to drink more deeply and gain the nutrients they will need for the spring.
While the soil is sandy silt and we will need to water again before too long, the fast-draining soil mitigates the risk of flooding. We also have well-established cover crops, which slow the velocity of run-off and reduce erosion. They also help reduce the soil compaction caused by the rains, as the roots help keep the soils relatively soft and loose. (Keep an eye out for a future blog post to hear about the many benefits of Hilliard Bruce’s cover crop program!).
If we don’t get 1 inch of rain per month in the winter, then we will supplement by applying 1 inch of irrigation water via the sprinkler system. Sprinklers in the winter are better than drip because it covers the entire rooting zone rather than just that found directly under the emitters.
Irrigation management is very important in viticulture, and this just scratches the surface. What would you like to hear more about? Leave a comment or send us an email – we love learning, talking, and sharing information about our sustainable programs!
See you next month as we explore another aspect of our SIP Certified vineyard and LEED Silver winery!