A challenging year demands precision
It is July 17th, and harvest is already underway. 2026 is the earliest vintage in nearly half a century, and that’s presented some unique challenges. As a viticulture consultant specializing in irrigation, I wanted to go under the hood and talk about how we managed this growing season. Specifically, I wanted to illuminate what technologies we used and how we used them to get us here…to harvest…in July.
Get ready for it…soil moisture
We talk a lot about soil moisture and for good reason. Soil moisture probes let you know how much water is in your soil, where the water is, where roots are active, and how irrigations behave in your soil. If there was one piece of equipment that was imperative this year, soil moisture probes are it. The reason being that this year, in addition to being early, was relatively wet. Even here in the Central Coast we got a solid amount of rainfall with much of it falling in late winter/early spring. Rainfall makes a lot more nutrients available for the vines compared to drip irrigation since rain wets a much larger surface area and, hence, soil volume. The fact that a warm February had budbreak popping off early meant that vines were able to tap into this ample moisture and the nutrients in solution. Canopies started out looking great!
…until they didn’t. Plummeting temperatures in April and May shut put the brakes on shoot growth throughout much of the state. Short shoots? Uneven growth? Stunted tendrils? …During bloom?? I guess I should water, right?
If you had a probe (or were using the one you have but usually ignore), you would see that you were most likely at field capacity and your stunted growth was instead owed to average temps that barely climbed above 60° Fahrenheit (keep in mind that growth essentially stops below 50° (10°C).
Behind door number two: plant stress sensors
Phenolic development is heavily influenced by water stress in lag phase and veraison, when your tannins and anthocyanins are forming. For example, we aim for water potentials around -13 to -15 for Cabernet as a pressure bomb measurement during these periods. For Pinot noir, it’s more like -11 to -13 bars. In a normal year, we have all summer to build stress, hitting maximum stress levels around late July/August. We’re a month early this year. Vines were sliding into lag phase while the profile was still full from all this spring rainfall, compounded by excessive irrigation from panicking growers. Depending on soil type, a lot of vineyards didn’t dry out enough to reach even moderate stress levels.
That brings me to plant stress measurements, which is what I really care about after all. There are a number of ways to quantify how stressed your vines are. The most ubiquitous is the pressure bomb that measures leaf water potential i.e. how much tension is in the xylem. Pressure bombs are clunky and only give you as many measurements as you care to take during the hottest part of the day. A few years ago, we switched to using Florapulse microtensiometers, which track water potential every 15 minutes. I can’t explain enough what a game changer these sensors have been and I’m still astounded at how few growers have adopted them, especially for a crop like winegrapes. Knowing how stressed vines are, and historically, how stressed they get at different soil moisture levels, help track exactly how far I can push vines.
And you can push vines too far! Although I find very few growers who actually do. Yellowing basal leaves are a tell-tale sign of a vine that needs water. It would be better to know you’re running out of water before vines start abscising their photosynthetic machinery (and your vines’ built-in shade cloth!). Depending on soil, variety, and rootstock you may not be able to resurrect vines that have already made the physiological decision to close up shop for the season. Soils with poor percolation for instance are notorious for crashing. Vines in these soils have nice deep roots that are extracting moisture from the bottom of the profile. When that runs out, you suddenly find you can’t get water past 16”. The vine needs to have active roots up top to take over when the deeper roots run dry. If you’re waiting for vines to crap out before you turn on the water, you’re going to hit a big speed bump.
In sum
As an irrigation specialist, these tools allowed me to be aggressive…very aggressive…especially in places where I know phenolic development is top priority for the winemaker. Every drop of irrigation water that wasn’t needed set us back a week from our target stress levels and this year, a couple weeks is all we had to build a whole season’s worth of stress.
You can spend a ton of money on technology right now if you want, but soil moisture probes and plant stress monitors are relatively inexpensive. Maybe you have some probes installed and you just don’t know how to use them. Here at Advanced Viticulture, we make technology work for you so you can make the best decisions.
Looking to get more from your vineyard technology?
Advanced Viticulture works with growers throughout California to interpret soil moisture, plant stress, weather, and irrigation data. Through our AVterra platform, we also integrate sensors into one dashboard and deliver practical irrigation guidance.
