In the vineyard

Pruning in Ontario: why growers leave extra buds

Pruning decides next year's crop. In most regions it is a balance between yield and quality; in Ontario there is a third term in the equation, because some proportion of the buds a grower leaves in March will already be dead.

Cane and spur, and what they mean

Winter pruning removes most of the previous season's growth. What is kept determines where next year's shoots — and therefore next year's fruit — will come from, because grapevines fruit on shoots growing from buds laid down the summer before.

In cane pruning, one or two long canes of eight to fifteen buds are retained from last year's wood and tied along the fruiting wire, and everything else is removed. In spur pruning, a permanent horizontal arm called a cordon is kept, and short spurs of two or three buds are left along it. Cane pruning takes more skill and more time but gives the grower a fresh choice of wood each year; spur pruning is faster, more easily mechanised, and locks in a structure that stays for years.

Both are used here. The choice follows variety, training system and the grower's labour situation, and it interacts directly with winter: a permanent cordon is a larger piece of irreplaceable wood to lose in a bad year, while cane pruning renews the fruiting wood annually from whatever survived.

The Ontario adaptation: prune late, prune twice

The textbook advice is to prune in the dormant season, and in a mild climate the timing within that window matters little. Here it matters a great deal, and the common practice is to delay.

A grower who prunes in December has committed to a bud count before knowing what January will do. A grower who waits can assess bud survival first — by cutting buds open and looking at whether the primary bud tissue is green or brown — and set the count accordingly. Many prune in two passes: a rough pass that removes the bulk of the wood without making the final decision, then a second pass once the winter has declared itself. It costs an extra trip through the vineyard and it is worth it.

Counting buds against a loss you expect

The arithmetic is straightforward once the survival rate is known. If a block would normally carry thirty buds a vine and assessment shows a third of the primaries dead, the grower leaves more buds than usual so that the surviving ones still produce a full crop. Leave too few and the vintage is short; leave too many in a year with little damage and the vine overcrops, ripening is delayed, and in Ontario delayed ripening is not a small problem — it is the difference between clearing the appellation Brix minimum and not. The harvest page covers those thresholds.

Grapevines also carry secondary and tertiary buds inside each compound bud, which push if the primary is killed. They are a genuine safety net and a partial one: secondary shoots are usually less fruitful, and a crop carried on them is smaller and later.

Where the information comes from

Bud assessment is a vineyard task, but the regional picture is published. Brock's VineAlert programme samples bud hardiness by variety and sub-appellation through each dormant season, which tells a grower what to expect before they start cutting — and whether this was a year to leave extra wood. The winter protection page covers the other defences, and the climate page the temperatures behind them.

What else pruning decides

Beyond bud numbers, pruning sets the shape of the vine for the season: how much canopy will develop, how exposed the fruit will be, how much air will move through the cluster zone. That last point connects directly to disease pressure, because an open canopy dries faster after rain and a dense one does not, and in a humid Ontario summer drying time is the difference between a clean crop and a rotten one.

It also has to serve the following winter. Vines that will be hilled up or buried need their structure kept low and flexible enough to work with, which is a constraint a grower in a warmer region never has to think about. The vine year page places pruning in the sequence of the season.