Spring and early summer in the vineyards is when the wine is truly made. Springtime for a viticulturist is like fighting a war, or like surfing a huge wave, depending on whether you’re a man-against-nature type or you tend to eat mushrooms and marvel at its magnificence. Either way there is no question that it is the most intense time in the vineyards. Mother Nature deals her hand in the spring, and how the cards are played translates directly into the finished wine. There is always a battle for time and resources in the vineyards, so during the early canopy growth period the viticulturist has to constantly evaluate the vines and form a strategy, prioritize, and then execute—and then, of course, change everything the next day when the weather shifts. Spring and early summer is the most stressful time of the year in the vineyards—it’s a relief when the vines settle into their mid-summer routine. By the time harvest rolls around, there isn’t much to do but pick the grapes—long hours, but straightforward. Just one task, don’t screw it up. During the spring there are a million things going on at once.
The Rhythm of the Season
Before getting into the details of the spring practices I want to describe the seasonal context. Bruce Cakebread once described the inexorable march of summer days as the “drumbeat of the vintage.” The season thumps along at its steady rate, and we have to somehow sync the vine phenology to that drumbeat (“phenology” is the term used to describe the seasonal progression of the plant—budbreak, bloom, veraison, etc. are phenological stages). Wine quality is dependent on keeping up with the drumbeat. What you do is less important than when you do it. As the old saying goes, “the difference between a good farmer and a bad farmer is two weeks.”
A major part of viticulture has to do with syncing phenology to the season. It starts with selecting varieties and rootstocks for a certain site. Are we on the Sonoma Coast or in Calistoga? North-facing or South-facing aspect? Pinot noir will get ripe too quickly in Calistoga, whereas Cabernet sauvignon might never get ripe in Freestone. This is obvious, but the same thinking drills down to many little decisions, such as timing of pruning, cover crop regime, irrigation, trellis style, canopy size, irrigation, and timing and style of leaf removal. These all have subtle effects on phenology.
While walking a vineyard together, Warren Winiarski once told me, “the vines keep getting bigger until the summer solstice, and then they start getting smaller.” That simple little observation—something he had learned from Andre Tchelistcheff—is absolutely the case, and it describes the crux of the seasonal rhythm. The summer solstice is usually June 21st, and that date should mark the end of canopy growth. It also loosely coincides with hardening of the seeds, which is where berry growth stops and ripening starts. Continued growth of the vines after that date will severely impact wine quality—less color, less concentration, green characters, less ripeness. On the other hand, vines that stop growing too much in advance of the solstice are typically excessively stressed, and can show in the wine as hard tannins, lack of high-tone aromas, bitterness, and a general lack of “generosity.”
Part of the job of the viticulturist in the spring is to guide the vines so that they grow normally and on schedule and then slow down and stop around the summer solstice. This means that one has to watch the shoot tips all spring, constantly assessing whether they are growing too fast or too slow. If they are growing too fast, shoot-thinning can be delayed, soil cultivation can be delayed or forgone, weed control can be delayed (not forgone—meadow mice can attack the trunks if weed cover remains around them throughout the season), and any irrigation water or fertilizer can be withheld. If the vines are growing too slowly they can be shoot-thinned early to remove competition, watered, or fertilized; or the soil can be cultivated, and fertilizers and growth enhancers like seaweed can be included in powdery mildew sprays.
However, Mother Nature dictates the vintage: while we have quite a bit of control over vine growth, we don’t have much control over bloom date (other than choosing the variety and rootstock) and bloom is the most critical moment of the entire season. The shoots can be long or short, but bloom is going to happen when it is going to happen. Not only is it fraught with risk—rain, heat, cold weather—but the timing of bloom pretty well defines the timing of harvest. Most vineyards have a consistent number of days from bloom to harvest, and so the timing of bloom dictates the timing of harvest. A late bloom means a late harvest, and all of the fall rains, slow ripening, and lack of a post-harvest vacation that comes with that gloomy scenario. So in addition to trying to protect the bloom with sprays (organic or conventional), tipping the shoots if fruit set is an issue, and pulling tissue samples to send to the lab for nutrient analysis (to guide fertilization), the bloom date is always carefully recorded to predict harvest dates and compare seasons. Once the bloom date has exposed itself, we get back to managing whatever we can to keep the vines in good shape given the hand we were just dealt.
Annual activity timeline...with year round gopher trapping
After the vines wake up and budbreak occurs, which is typically in March or April, the first spring pass through the vineyard is for shoot-thinning, or suckering. This is a slow and laborious pass. It is our chance to correct any pruning errors, to follow up on the pruners’ strategy, and to again shape the vines, so it is a skilled operation. The basic principle is to leave one shoot growing from each bud retained at pruning time, and rip off and/or rub out everything else. With cane-pruned vines, this is also the time to select well-placed suckers in the head of the vine to serve as canes for the following year. The vines start out looking like bristle brushes, and at the end of the process they have nicely spaced shoots.
Shoot-thinning is such a slow process that it takes several weeks or up to a month to complete the entire vineyard(s). If it is done early then the retained shoots grow more vigorously. If done late then the shoots to be retained are held back. For this reason the weakest areas in the vineyard are always done first, and the strongest areas are done last. Timing of suckering is a key viticultural tool. Too early and you have to go back again and clean off the regrowth—but it is sometimes worth it if the vines are very weak and need that much of a boost.
Shoot-thinning affects the quality and quantity of the fruit set. For instance, two shoots often grow out of the same bud on a vine. If the vine is spur-pruned, extra shoots on each two-bud spur are removed, because only the two main shoots will give good fruit. With cane-pruning, if there is space on the cane and the crop looks low, you can leave the “double” shoot to get a bit more fruit, or to get more shading on the fruit. Since bloom hasn’t yet occurred during the shoot-thinning stage, we don’t know exactly what our fruit set will be, but we can already see the flower buds, so we can do counts and get an idea of what we have going into the season.
After shoot-thinning but before bloom, the shoots are guided into position on wires in trellis systems. If done correctly, the shoot tendrils will attach to the wires, and remain in place even during extremely windy conditions. This is an activity where timing is everything. It is imperative that the shoots are positioned straight up and down, and do not overlap each other. Floppy, piled-up shoots are a major cause of green flavors, poor acidity (high potassium in wine), poor color and poor ripening, as well as a pathway for disease problems. The green flavors, poor color, and poor ripening are due to blocked light; the poor acidity results from deep shade, causing shaded leaves to turn yellow and senesce, exporting their potassium to the fruit; and disease occurs because it is physically impossible to get sprays inside zones of such densely packed leaves.
Leaf or Lateral Removal
After the shoots are thinned and positioned, the next step is leaf or lateral removal. To define the terms, “leaves” are the main leaves on the shoot (one per node), and “laterals” are the mini-shoots that arise from the axillary buds at the base of the leaves. In California, where sunburn is a concern, we have moved to removing laterals to thin the canopy out a bit, but leaving the leaves for protection from the sun. In places like Oregon, where the sun is less intense and disease pressure is high, both leaves and laterals are removed.
Typically, leaf or lateral removal immediately follows fruit set (fruit set marks the end of bloom, when the berries that were fertilized stick on to the rachis, and the rest fall off). A few people do leaf removal before or during bloom to try to maximize light from day one. This is thought to decrease fruit set, perhaps from a wounding response, or possibly reduced carbohydrate nutrition due to the reduced leaf area adjacent to the flower—it’s not really known if or why bloom-time leaf removal reduces set. It’s done in places like Germany where they have tight clusters and very high disease pressure, so they want to reduce set and get a more open cluster. For the rest of us, though, since we don’t want to endanger bloom, we wait for the fruit to set and then remove leaves or laterals. Like shoot-thinning, this is a slow activity, so it can’t all be done at once; unlike shoot-thinning, the vigorous vineyards are done first, because they need the light and air movement around the clusters, and the weaker vineyards are done last, if at all.
Which leaves or laterals to remove is determined by the row orientation. The basic concept is that morning light is good, and afternoon light is bad. Hot afternoon sun on the fruit is to be avoided. Even if sunburn isn’t evident, the baking sun will leave reduced levels of anthocyanins and aromas in the fruit. Morning light, on the other hand, will stimulate the production of anthocyanins and aromas. So on East/West running rows, we thin out the North side, and on North/South running rows we thin out the East side.
On Northeast/Southwest running rows—the best row orientation in a warm climate as it balances the heat load on both sides of the canopy—it gets trickier. In this case, if the vines are balanced, you can do nothing; if vigorous, you can thin the leaves or laterals in the interior of the canopy, leaving a protective shell of leaf cover on both sides. I tend to leave the fruit zone alone, and thin laterals only a few inches up above the clusters, letting diffused light trickle down from above. Leaf and lateral removal is very particular to the individual viticulturist, much more so than the other canopy management activities. Most viticulturists have their trademark leaf removal method, and it’s a major point of contention between them. Driving by a vineyard you can often tell who farms it by looking at the leaf removal.
When the vines have an obvious cool side, the fruit can be quite exposed. If there is no obvious cool side then one has to be more careful. Either way, though, the upper portion of the canopy has to be addressed as well. In this case, the goal is not to adjust the light on the fruit, but to alter the entire canopy. If we have dense shade even after good shoot positioning we need to pluck out strong laterals until specks of light can be seen coming through from the other side. Richard Smart, who is a bit crude, describes a perfect canopy as one where “there are enough gaps in the canopy that you can peak through and watch a person undressing, but there are enough leaves that they can’t see you standing there watching them.” He’s a great viticulturist, but a bit creepy. Good image though.
Tipping, Topping, and Hedging
The most visual steps in spring canopy management are tipping, topping, and hedging. These activities are variations on the basic concept of cutting back the length of the shoots. Tipping is just cutting off the shoot tips, topping means cutting the shoots back quite a bit, and hedging refers to cutting back the sides. The perfect boxed-in hedgerow of vines is the result of topping and hedging. It is more than a visual postcard shot, though: there are viticultural reasons for the practice.
Tipping at bloom can be slightly effective in attaining a better fruit set (more berries per cluster). This is a big issue in varieties like Malbec or Merlot that tend to shatter at bloom. Removing the shoot tips diverts energy to the flowers. Also, in all varieties, tipping only the strong shoots but leaving the shorter weak shoots improves shoot-to-shoot uniformity by temporarily stunting the strong shoots, allowing the shorter shoots to catch up a bit.
Topping is typically done after bloom, when the shoots are starting to slow down. The goal with topping is to alter the leaf area-to-fruit ratio. Reducing the leaf area slows down sugar accumulation, reduces water usage, and limits carbohydrate storage for the following season, reducing vine vigor. These effects can be positive or negative, depending on the goals. Topping at a consistent height aids vine-to-vine uniformity as well, since both strong and weak vines are restricted to the same amount of leaf area.
Topping at 14 leaf nodes is fairly common in the Napa Valley, but considered excessive in parts of Europe, such as Burgundy, where 10 leaf nodes is more common. When production of tonnage is the goal, such as in Modesto or Fresno, 24 leaf nodes are common. A newer strategy for California is to top at 16 leaf nodes to provide the leaf area needed to fuel veraison, then to top again after down to 12 leaf nodes after veraison to reduce the rate of sugar accumulation. If the weather turns cool at veraison and we want more sugar accumulation, the vines can be left at 16 nodes.
Hedging the sides of the vines is tricky for the tractor driver—the knives of the hedger whirl dangerously close to the trellis stakes and wires—but it can skim off the outside layer of laterals on vigorous vines, improving the canopy microclimate and reducing leaf area that would otherwise be used by the vine to grow roots to be even stronger the following year.
Vines prior to hedging
Vines after hedging
Fruit-Thinning (Green Harvesting)
The two principal times for fruit-thinning, also known as green harvesting, are in the spring and at veraison. The purpose of spring fruit-thinning is to balance the crop load with the vigor of the vine by removing fruit from weak shoots and third clusters, and to eliminate clumping. This is the last of the main spring activities.
Before doing much thinning its important to figure out how much fruit is on the vines. An easy way to fail as a viticulturist is to surprise everyone by showing up on the crushpad with way more or way less fruit than the winemaker expected. The crop estimate is one of the core bullet points on the viticulturist’s job description. The winemaker needs to know how much fruit will be coming in so that they can plan for cooperage, and the owner is concerned with cash flow.
Shortly after bloom we count the clusters on a number of vines to get an idea of what we’re dealing with in each vineyard. The number of clusters per shoot varies quite a bit from year to year, depending on the weather the year before. This is because the grape cluster primordia—kind of like the embryonic form—actually form in the bud as it is developing on the newly growing shoot in the spring. To be clear, these are the clusters for the following year. Over the course of the summer those canes harden, they are pruned in the winter, and finally those buds push up in the following spring. If the weather was good the previous summer there will be two or even three large clusters on that shoot. If the weather was cold and rainy there will only be one or two smaller clusters.
The most common time to thin fruit is at seed-hardening (also called lag phase). This marks the time that the cells in the berries have stopped dividing, but haven’t yet started to expand prior to veraison in the course of their final ripening push. Thinning when the berries are still growing (before seed-hardening) causes the vines to compensate for the crop loss and make the berries bigger. If the vines are weak they should get thinned earlier to propel berry growth, but if the vines are strong then the berries can really blow up if thinned too early.
Thinning too late after seed-hardening can be a waste, since the effect of thinning fruit diminishes quickly as the season progresses, to the point that close to harvest 75% of the fruit needs to be thinned to get an increase in brix similar to thinning 25% of the fruit at seed-hardening.
Since seed-hardening is a predictable stage in the berry development, it is the next opportunity to guesstimate the crop size after bloom. We cut off 20 or 30 clusters and weigh them. The rule of thumb is that the berry size will double between seed-hardening and harvest. So we take our cluster weight and multiply by two. We already have the cluster count per vine from bloom-time, so figuring out tons per acre is pretty easy. This helps guides the severity of thinning. If the crop estimate is too low then we thin less, and if a bumper crop is expected then we thin hard. The goal is to achieve a normal-sized crop.
A vine prior to thinning
The vine after thinning
No matter how well we execute the pruning, shoot-thinning, shoot-positioning, and tipping, there are always a percentage of the shoots which don’t develop properly, and the fruit from these shoots is inferior. Typically these shoots are placed in two categories: if less than 18 inches in length all clusters are removed, and if less than 24 inches in length only one cluster is retained on the shoot.
One of the viticultural principles that most people agree on is that a shoot should have a maximum of two clusters. There is occasionally a third cluster on a vine, and that cluster typically doesn’t ripen properly. The varieties can really differ on their predisposition for excessive numbers of clusters: Petit verdot can produce up to five clusters on a shoot, whereas Merlot rarely produces a third cluster. Either way, removing any third clusters is a standard practice.
This is also the time to thin out clumps of fruit. No matter how good the job of winter pruning, there are always shoots that are too close together, causing the fruit to get bunched up. It is critical that each cluster has room to hang separately from the adjacent clusters. If fruit is clumped together, the clusters on the interior of the clump will remain pink and watery and be more susceptible to powdery mildew or bunch rot. The clumps need to be separated and thinned out before the berries swell and soften. If the clumps aren’t thinned in time, the fruit will get tangled together as it grows and be impossible to separate.
And that’s it. We’ll go over all of the spring tractor jobs, like spraying, mowing, discing, spading, weed control, and how they influence wine quality and character, at another time.
Steve Matthiasson makes classically balanced wines under the Matthiasson label, and consults on vineyard practices for a number of wineries, including Araujo, Spottswoode, Stag’s Leap Wine Cellars, Chappellet, Hall, David Arthur, Long Meadow Ranch, Limerick Lane, Duckhorn, and others.
Augie, I approach soil type as it affects vine vigor, water availability, nutrient balance, etc., so in that sense, soil type is the basis of decisions, but mainly in how it now it affects vine growth and development--soil type affect on wine flavor independent of vine growth is part of terroir, but not really a viticultural parameter, unless it is something that can be managed, like high potassium effect on wine pH, in which case we might add lime or gypsum. To answer your other question, favorite soil types are alluvial fans--also called benchland--deep, well drained, lots of nutrients but lower in vigor, make wine with good balance of structure and aromatics.
Also, what is your favorite/most challenging vineyard/vintage to work with?
Great Article. Having just read the soil for sommeliers article, I would be tempted to ask how much soil type plays into your viticulture regime, or if more or less the focus is vine vigor, and that may depend on soil type, but the soil type isn't the basis of the decisions???
Thank you Steve!
This is a fantastic, and wonderfully clear explanation of these vineyard practices. I have attended the vineyard management classes at UC Davis extension, and read books, but this was so clear, practical and enjoyable.