NEWS / FEATURES

Fruit by the Foot

Spacing and other factors affect tons per acre

VineSpeak

Jessica Cortell received an M.S. degree in horticulture and a Ph.D in food science and technology from OSU. She owns Vitis Terra Vineyard Services and teaches at the Northwest Viticulture Center in Salem.

Oregon has tons of grapes this year — literally and metaphorically. For those not in the industry, winegrapes are generally tracked and sold as tons of fruit; and as you know, a ton equals 2,000 pounds. When referring to the fruit in the vineyard, the discussion often revolves around “tons per acre.” Winemakers frequently request a specific cropping level using this measurement as a guide. 

Back in the day of 10-foot row spacing, maybe the preference for 2 tons per acre made sense, but should we be applying the same metrics to 5-, 6- or 7-foot row spacing? Let’s play around with some numbers and assumptions.

First assumption is that the fruiting wire is filled with productive shoots in all vine densities so that row spacing is the main factor affecting yield potential on an acre basis. Second, we will assume a similar shoot density of one every 4 inches. Let’s assume a cluster density of 1.5 clusters per shoot and an average cluster weight of .22 pounds (average weight of a Pinot Noir cluster) and a price of $3,000 per ton of fruit. These assumptions lead to a cluster weight of about 1 pound per foot.

As seen in the vine density worksheet, all have the same amount of fruit, around 1 pound per foot, but the yield potential on a per-acre basis is significantly different going from 2.16 tons per acre to 4.31 tons per acre. These numbers clearly show where the preference for 2 tons per acre originated in Oregon. It was based on many of the early vineyards with wide row widths from 10 to 12 feet. In terms of crop load, maybe it made sense for those early plantings for cool-climate grapegrowing, but perhaps we need to use the metric of pounds per foot instead of tons per acre in many of the new high-density plantings.

Winemakers should be mindful of these metrics as they determine crop loads for vineyards with different row widths. A vineyard with 6-foot row spacing should, theoretically, be able to be cropped at 3.5 tons per acre. While this is a good guide, a grower also must consider the vineyard site and what it can ripen in a given vintage. Lack of available water due to shallow soil or lack of irrigation can impact what the vine has the capacity to ripen. A vineyard with high drought stress might have a canopy challenged to ripen the fruit. 

The one pound of fruit per foot seems to be a sound guideline for Pinot Noir in the Willamette Valley. Some high-end brands will crop their reserve blocks sometimes as low as .5 pound per foot. This, of course, raises the yield-versus-quality question. The decision whether to crop higher or lower will be a reflection of the site and winemaker’s wine style. The vintage, whether hotter or cooler than normal, can also influence how many tons per acre a winegrower wants to take a gamble on ripening.

This year, many vineyards are hanging a good crop load since fruitset was favorable and warm conditions have prevailed to give growers confidence in ripening the crop.

With harvest in full swing, many flatbeds and trailers are moving up and down the valley as winemakers get the crop into wineries. Be mindful of the extra traffic, as many tons of grapes will be on the road through the middle of October.

 

Assumptions:
1. Vine shoots are spaced 4 feet apart.
2. Average grape cluster weighs 100 grams (0.22 pounds).
3. There are 1.5 clusters per shoot.
4. The price is set at $3,000 per ton of fruit.
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