History of Our Vineyard - Budding and Flowering
Budburst is fundamentally the awakening of the plant after the dormancy that happens during winter and occurs based on the nutrients accumulated by the plant in the previous year.
The dormant buds swell and begin to push back the protective scales of the "eyes". A sort of fuzz appears and the first leaves emerge. The first buds to hatch are those at the end of the shoot (climbing effect of the species), delaying or inhibiting the hatching of the proximal buds. Growers in continental climates take advantage of this phenomenon to defend themselves from frost by pruning late
Although cellular activity rebirth starts at 5ºC, budbreak, or vegetative growth, needs a higher temperature that is between 8ºC and 12ºC. This value depends on the grape variety, the latitude, and the vigour of the vine, but will always be around the so-called 'vegetative zero', which is around 10ºC.
The budbreak rhythm or speed depends on the rigour of winter temperatures and fundamentally on the atmospheric heating rhythm. It may be slow if the atmospheric warming is progressive; or fast, if there is a prolonged warming after a winter. The strong sensitivity of the first green organs to frost, even if moderate, makes budbreak one of the most critical periods in the vegetative cycle of the vine. In places where the continental influence is felt (in particular, throughout the interior of the country, with special incidence in the northern half), one may opt for late budbreak varieties.
In the Northern Hemisphere, budbreak happens between March and April; in the Southern Hemisphere, between September and October.