MSU Extension Grapes

Canopy management is a critical component of successful viticulture, especially in cool climate regions such as northwest Michigan. Among the various practices involved in canopy management, shoot hedging, or "topping," plays a key role in optimizing the photosynthesis of grapevines in supporting fruit ripening. While traditional approaches often recommend delaying hedging until later in the growing season, recent research by Michigan State University (MSU) in collaboration with industry partners suggest early hedging can provide significant advantages in cool climate vineyards where the growing season is short and ripening windows are limited.

In the past, canopy hedging was often postponed until the shoot tips had grown well above the top wire and had even begun to bend back into the canopy. At that stage, hedging involved removing a large portion of the canopy. Research by the Department of Horticulture at MSU showed that such extensive removal negatively impacted photosynthesis and reduced carbohydrate allocation to the fruit. Instead, the new approach is to hedge earlier when the growing shoot tips are just reaching the top wire. This minimal removal of vegetative growth provides two key benefits:

1. It preserves a greater portion of the photosynthetically active leaf area.
2. It stimulates the development of lateral shoots, which later become an important source of carbohydrates during fruit ripening, starting at veraison.

This has been demonstrated in trials held at Lemon Creek Winery and Brys Estate by Michigan State University Extension specialist and professor Paolo Sabbatini and his team. The treatment resulted in an increase of up to 2 degrees Brix at harvest. In many cool-climate vineyards trained to vertical shoot positioning systems, shoot growth continues vigorously well past the top wire. If left unmanaged, these shoots can shade the fruiting zone, reduce airflow and suppress the productivity of interior canopy leaves. A common recommendation is to hedge once shoots begin to bend or fall over the top wire. However, this approach can result in the removal of the youngest and most photosynthetically active leaves, the exact leaves needed during the critical ripening period.

Leaf age is a key determinant of photosynthetic efficiency. Basal leaves, located near the fruit zone, may be 120 to 150 days old by late summer. These older leaves often exhibit reduced photosynthetic activity due to age, disease pressure or self-shading. In contrast, shoot tips contain leaves that are just a few days to a few weeks old. These young leaves are highly efficient at producing carbohydrates, especially important as the vine shifts its energy toward ripening clusters.

When hedging is delayed until these shoot tips are fully developed and bending over, growers risk removing the very leaves that could have supported ripening. In contrast, early hedging, performed when shoots are approximately 10 to 15 inches above the top wire, can promote a more balanced canopy and initiate lateral growth early enough for those new leaves to mature and contribute during the peak ripening window. These lateral leaves often reach full maturity at a time when the original primary leaves are aging and declining in efficiency.

The result is a canopy with a higher proportion of mid-aged leaves (approximately 30–50 days old) during late summer, an ideal age range for maximum photosynthetic contribution. By maintaining a younger and more efficient canopy, early hedged vines were better able to improve sugar loading during fruit maturation.

Additionally, early hedging reduces the risk of excessive shading in the fruit zone, improving light penetration and airflow. These conditions are critical for disease management, particularly in humid climates where powdery mildew and botrytis can thrive in dense canopies. Early removal of shoot tips also limits carbohydrate competition from excessively vigorous apical growth, redirecting vine energy toward fruit development and ripening.

It’s important to note that hedging too early, before the completion of the fruit set, may lead to excessive lateral growth in vigorous cultivars (e.g., Cabernet Franc, Marquette), overly fertilized or planted with vigorous rootstock in rich soil and at low planting density, leading to a dense canopy. However, when timed correctly, shortly after fruit set and as shoots extend modestly beyond the top wire, early hedging provides a strategic balance. It initiates timely lateral growth while preserving the most productive parts of the canopy.

Early hedging should be considered a standard practice in cool climate viticulture. By hedging when shoots are just 5 to 10 inches above the top wire, growers can maintain a younger, more efficient canopy, support consistent ripening, and improve overall canopy health and fruit quality. This practice is especially critical in regions like northwest Michigan, where the window for ripening is narrow and efficient canopy function during late summer can make the difference between marginal and optimal fruit maturity.