Summer in the Vineyard Sets the Stage for Harvest

Sonoma County, California / Getty

For some people, summer means warm temperatures, long days and carefree vibes. For vignerons, summer is hard work. After they prune and prepare the vineyards through the winter and spring, winemakers must shepherd grapes to the finish line. They pull leaves and drop fruit, monitor for diseases and pests, and protect against weather hazards.

Life of the Vine

Summer sets the stage for harvest. The vines go through the critical stages of fruit set, veraison and ripening. Harvest for some earlier-ripening varieties in hotter regions now starts in the summer, too.

As spring ebbs into summer, flowers develop a seed and grape berry. This phase, fruit set, establishes the amount of crop the vineyards will yield, and the amount of wine they will produce.

The vine’s berries are small, hard and green. High in organic acid, they have little sugar. Summer’s heat triggers the grapes to ripen, much like cherries and blueberries. As a grape’s glucose and fructose increase, acids levels drop.

Summer in the vineyard verasion
Veraison is when a grape accumulates color / Getty

“For me, summer is the time when I can see the finish line,” says Dana Grande, grower relations manager at Jordan Winery. “Vine growth is slowing down, most management tasks are completed and we are awaiting veraison for our final thinning pass.”

Veraison is when a grape accumulates color, much like how a pale strawberry turns bright red. White and gray grapes like Pinot Gris turn yellow, gold and even pink, while red varieties become maroon, purple and black.

In white varieties, the color changes as chlorophyll is replaced with carotenoids. In red grapes, the pigment comes from anthocyanins.

During this time, tannins and other phenolics increase until the grapes have reached the optimal picking window. This window represents the winemaker’s ideal balance of sugar and physiological or phenolic ripeness. The grapes have the exact flavor, color, potential alcohol, structure and texture sought.

Spring in the Vineyard Brings Hope and Rebirth

Vineyard Management

In warmer years and regions, tasks like preventative mildew spraying, fertilization and shoot thinning and positioning occur in the spring.

“In summertime, the living is a bit easier,” says Grande. “Springtime is so busy. We need to be everywhere doing everything and the minute we begin, we are falling behind.”

As summer hits, the pace at Jordan slows. “It is nice to take a breath and focus just on managing the vine’s balance,” says Grande. “Mostly, the vines have achieved their maximum shoot length, and it’s our job to maintain those shoots and leaves.”

Canopy management is the complex process of balancing sunlight, shade and air circulation around fruit clusters. Leaves shade fruit and protect them from heat and sunburn. However, vigorous leafy growth can create too much shade and stifle air flow. This can foster mildew, mold and other diseases like black rot from fungus.

Leaf removal and positioning shoots offers balance for optimal ripening and airflow. Vineyard managers strive for “not too little, not too much,” says Grande.

Summer in the vineyard pruning
Summer sets the stage for harvest / Getty

Summer Hazards

Heat, drought, rain and humidity can affect the ripening process and vineyard work.

Excess heat halts photosynthesis. When temperatures soar above 95°F, vines shut down in a bid for survival. Climate change has increased the frequency of heatwaves, and average temperatures in some regions continue to climb.

“In recent years, we have had periods of very high temperatures compared to the averages of the last 20 years,” says Rui Flores, agriculture manager at Herdade do Esporão in Alentejo, Portugal. “Since 2014, we have witnessed the six hottest years on record.”

“With temperatures rising, grape variety cycles are reduced and achieving balanced ripening is more difficult,” says Flores.

The Unexpected Vitality of Winter in the Vineyard

Heat also limits vineyard work. Teams shift their hours to the early mornings or cut down until it’s safe to resume.

Soils can dry due to heat or lack of rainfall. This can help the vine as it reduces vigor. In severe cases, the vine’s roots produce a hormone called abscisic acid (ABA), which prompts the plant’s stomata to close and conserve water.

Why does that matter? Transpiration is the process of how water moves through a plant. On growing plants, water evaporates continuously from the surface of leaf cells, called stomata. The vine’s roots replace lost water through uptake in moist soils.

When roots experience dry soils, the stomata closes to save water. The intake of carbon dioxide for photosynthesis stops, which halts ripening.

Summer in the vineyard grapes
Heat, drought, rain and humidity can affect ripening / Getty

In Sonoma, California, limited winter rain prompted some of Jordan’s winemakers to tweak their vineyard practices and address irrigation, Grande says.

“This year, we will be growing smaller vines, which may have less capacity to carry an average crop load,” she says. “Through frequent monitoring of the vine’s overall health and growth, we will maximize irrigation efficiency and apply water only when needed. Specifically, we want to alleviate stress with a small amount of irrigation prior to any heatwaves.”

Climate change is transforming regions that were traditionally cooler and wetter.

Dry conditions increase the threat of fire, too. Properties that survive such fires may have fruit tainted with smoke.

Too much rain and humidity can also cause problems and increase threat of disease.

“In a northern vineyard like ours, the challenges are to avoid mildew and botrytis, which are more prevalent in humid environments,” says Pierre-Jean Sauvion, winemaker at Château du Cléray. He’s also head of the communications committee at InterLoire, a trade group for Loire Valley wines in France.

Climate change is transforming regions that were traditionally cooler and wetter.

“We face more and more periods of drought in summer,” says Sauvion. “After the stress of frost in spring comes the stress of pests, drought and the risks of [grape] sunburns. Everything must be done to keep an optimal foliage for photosynthesis.”

But not all seasonal changes are marked as losses.

“While a dry summer can block the ripening of grapes, in the Loire Valley, especially for our reds, this is rather good news,” says Sauvion. “It gives us earlier vintages. The longer and sunnier days improve the ripening of our Cabernet Franc. We are reaching optimum technical and aromatic maturity.”

Hot air balloons Napa
Hot air balloons over Napa Valley / Getty

Summer is also the season of pests. Birds devour vineyards of sweet berries before winemakers can harvest them. Nets, though tedious and expensive, can stop the starlings, mockingbirds and finches that destroy crops.

Regardless of the challenges, winemakers adore summer.

“The vineyard is gorgeous, the days are long, and it’s the perfect time to welcome our friends to the Loire Valley,” says Sauvion.

Published on June 18, 2021
Topics: Wineries