Phenological Stages — Bud Break, Flowering, Fruit Set, Véraison, Harvest

Phenological stages are the steps in the grapevine's growth through the season, from the dormant winter bud to ripe fruit and, after harvest, leaf fall. The modified Eichhorn and Lorenz (E-L) system (Coombe, 1995) numbers these stages, so a grower can define the timing of a vine growth stage more accurately. Its major stages, in order, are budburst, flowering, setting (fruit set), véraison and harvest.

• Budburst, E-L 4: green tip, with the first leaf tissue visible
• Flowering, E-L 23: 17 to 20 leaves separated and 50% of caps off
• Setting, E-L 27: young berries enlarging (more than 2 mm in diameter), with the bunch at right angles to the stem
• Véraison, E-L 35: berries begin to colour and enlarge; just before it, at E-L 34, berries begin to soften and sugar starts increasing
• Harvest, E-L 38: berries harvest-ripe
• When stages are recorded in field trials, the date noted is when 50% of the tagged buds or shoots reach each stage

For much of the winter, buds are in a state of enforced dormancy, and once there they only need sufficiently high temperatures in order to burst. Buds reach this state in most temperate locations by early winter, so it is possible for them to burst prematurely in unseasonal warm weather. Higher temperatures in the latter part of winter advance the time of budburst. Flowering, also known as bloom, occurs once the flower parts are mature, and the mean daily temperature at the start of flowering can vary from 16°C to 20°C in Australian regions.

• The order of budburst of different varieties tends to be maintained: Chardonnay bursts relatively early and Cabernet Sauvignon relatively late
• Early bursting varieties tend to flower early; early flowering varieties include Chardonnay, Pinot Noir, Pinot Gris, Malbec and Touriga, while Carignan, Crouchen and Muscadelle are late season varieties
• At less than 15°C few flowers open, at 17°C they open normally, and at 20 to 25°C opening is rapid
• Better release of pollen occurs in dry weather; both rain and strong winds reduce pollen density
• Cool seasons delay flowering relative to warm seasons

Fruit set is the transformation of flowers into berries, following pollination and fertilization. Weather is one of the most influential and least controllable factors affecting it: temperatures below 59°F can delay cap fall and reduce the success of fertilization by slowing down the growth of pollen tubes. Low rates of fruit set do not necessarily mean low yields. Vines can offset low fruit set to a certain degree through increased berry size, an adaptive mechanism known as yield component compensation, and poor fruit set becomes a problem when it leads to a significant reduction in yield.

• Coulure is the excessive shedding of flowers and young berries, leaving relatively few berries; it is a symptom of poor fruit set
• Millerandage is an excessively high proportion of seedless berries and live green ovaries relative to seeded berries, and is also a symptom of poor fruit set
• Millerandage is often called hens and chicks: the normal, seeded berries are the hens, and the smaller berries with underdeveloped seeds are the chicks
• Millerandage can result from a combination of factors, including nutrient imbalances, early-season water stress and poor weather conditions around bloom
• Once flowering has started, low temperatures delay flower opening, which is often associated with retention of caps and poor fruit set

Berry development is described in phases. Phase 2, also known as the lag phase because the berry grows only slowly, lasts between 7 and 40 days, depending on both variety and temperature. Towards the end of this phase the berry starts to soften and to colour, and this is known as véraison. Véraison marks the beginning of Phase 3, the period of rapid cell expansion and sugar accumulation, and the stage at which berries mature and are harvested. Harvest is E-L stage 38, when berries are harvest-ripe. There are a number of ways to define ripeness, and the definition used depends on the wine style intended.

• Anthocyanins begin to accumulate in the skins of red varieties about two weeks before the colour is visible
• Sugar accumulation is generally more rapid in the weeks following véraison
• During ripening, malic acid in the berry is drawn upon and broken down to provide energy; the amount of tartaric acid per berry remains constant, but its concentration decreases as the berry increases in volume
• In the Willamette Valley, véraison occurs in about mid-August
• The ways to define ripeness include juice or pulp maturity, skin maturity, phenolic maturity, aromatic maturity and seed maturity; indicative juice targets are given as sugar (Baumé) and acidity (g/L)

There is an ever-present danger of low temperature injury to bursting buds and young shoots, and after bud break in spring, grapevine shoots are sensitive to frost damage. Around flowering, low temperatures delay flower opening, which is often associated with retention of caps and poor fruit set.

• After the early April 2021 frosts, the national wine union CNIV said 80% of French wine regions were affected, from Bordeaux and Burgundy to the Rhône and the Loire
• The Languedoc wine body CIVL said there were fears that between 30% and 50% of the potential Languedoc harvest may have been lost to the sub-zero temperatures
• Agreste, the statistics arm of France's agriculture ministry, forecast that French production in 2021 would fall by between 24% and 30% on the previous year; the ministry report said frost destroyed around 30% of first buds in Champagne, mostly Chardonnay
• Many winemakers lit candles and controlled fires next to rows of vines to help protect the emerging 2021 crop
• During temperature inversions, wind machines can be very effective at mixing the air and reducing the risk of frost damage

Growers can shift some stages a little. Spring pruning of spurs can delay bud burst and flowering compared to mid-winter pruning, and late winter pruning can slightly delay the phenology, but it can be detrimental if performed after shoots have 6 to 7 leaves unfolded. Leaving long canes when pruning delays bud break on the more basal part of the canes. Water stress can shorten the interval from bud burst to flowering, and from flowering to véraison.

• Timely shoot thinning helps to open the canopy, improving sunlight penetration and airflow; leaf removal during bloom can reduce fruit set
• The AWRI notes that since the early 1980s, harvest has advanced by about 8 days per decade in southern Australia, Europe and California, among other places
• In open-top chamber research in the Barossa Valley, with temperature raised 2°C above ambient over the whole season, higher temperature lowered titratable acidity and raised pH in some varieties, such as Chardonnay and Cabernet Franc, but had no effect at all on Shiraz

Primary sources: https://www.awri.com.au/wp-content/uploads/1_phenology_bud_dormancy_and_budburst.pdf, https://www.awri.com.au/wp-content/uploads/3_phenology_flowering_and_pollination.pdf, https://www.awri.com.au/wp-content/uploads/4_phenology_berry_development_1_and_2.pdf, https://www.awri.com.au/wp-content/uploads/5_phenology_berry_development_ripening_3.pdf, https://www.awri.com.au/wp-content/uploads/6_phenology_defining_berry_ripeness.pdf, https://www.awri.com.au/wp-content/uploads/grapegrowth.pdf, https://www.awri.com.au/wp-content/uploads/2014/09/on-farm-trials-manual-3-3.pdf, https://www.awri.com.au/wp-content/uploads/2014/11/exteme-temperature.pdf, https://www.awri.com.au/wp-content/uploads/2018/04/s1612.pdf, https://wine.wsu.edu/viticulture-enology-extension-news-spring-2025/, https://extension.oregonstate.edu/sites/extd8/files/catalog/auto/EC1639.pdf. Secondary sources: https://www.decanter.com/wine-news/fears-of-frost-damage-in-french-vineyards-456120/, https://www.decanter.com/wine-news/french-wine-harvest-2021-smallest-for-decades-463221/. Last verified 2026-11-02