Wine · Terminology

Budburst

The moment in spring when the vine's buds swell and open — and the frost clock starts.

Budburst — budbreak, débourrement — is the point in spring when the buds laid down last summer swell, split their protective scales and push out the first green shoots. It ends dormancy and starts the growing season.

The trigger is soil temperature, generally around 10 °C, so budburst comes earlier in warm regions and on well-drained, stony or sandy soils that heat quickly. From that moment the vine is vulnerable: a young shoot is killed outright by frost.

In practice

  • Early-budding varieties — Chardonnay, Grenache, Merlot — are the most frost-exposed. Late-budding ones — Cabernet Sauvignon, Mourvèdre, Riesling — dodge more of it.
  • Growers delay budburst by pruning late, or accept the risk and defend the vineyard with wind machines, sprinklers, heaters and helicopters.
  • Slope and air drainage matter enormously: cold air pools in hollows, so frost hits the bottom of a slope first.
  • Uneven budburst means uneven ripening months later.

Where you'll meet it

Frost defence, ranked by cost

Method How it works Notes
Site selection Slopes and air drainage keep cold air moving Free, and decided once
Late pruning Delays budburst by days to weeks Cheap, limited protection
Wind machines Mix warmer air down onto the vines Only works with an inversion layer
Sprinklers (aspersion) Latent heat of freezing water protects the bud Needs a lot of water, and the spray must not stop
Candles / bougies Direct heat, and mixing Labour-intensive, photogenic, expensive
Helicopters Same principle as wind machines Very expensive, sometimes worth it

The exam angle

Frost questions want the mechanism as well as the method: aspersion works because water releases heat as it freezes, wind machines work only when a temperature inversion puts warmer air overhead. Explain the physics and the mark follows.

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