I covered details in a few of these stages in previous posts (Please see Flowering and Fruit set, and Ripening.), but as I approach my exam in just a few days, I realize it may be helpful to have a consolidated list that covers each stage of a vine’s growth cycle to put those other posts into a broader perspective. Hence, the impetus for this post.
1. Dormancy (Nov.—March in N. Hemisphere; May—Sept. in S. Hemisphere)
Defined as the time between autumn leaf-fall and spring budburst.
A vine needs:
- Air temperature at or below 50°F—at this temperature it is too cold to grow, so the vine will remain dormant.
- Stored carbohydrates (found in roots, trunks, and branches) that were accumulated from the previous growing season.
Dormancy will fail if:
- Temperatures are too cold. Winter freeze is a real threat in some regions. At or below 5°F will damage vines; at or below -13°F will kill vines.
- Temperatures that are too mild will impede the vine’s ability to stay asleep (dormant).
2. Budburst (March—April in N. Hemisphere; Sept.—Oct. in S. Hemisphere)
Defined as marking the end of dormancy. Buds swell and open, and green shoots start to emerge. Timing of budburst is dependent on air and soil temperature, grape variety, as well as viticultural practices.
A vine needs:
- Average air and soil temperatures at or above 50°F.
- CLIMATE FACT: In regions that have stark contrasts in seasons (hot summers, cold winters, etc.) that happen quite quickly (as in continental climates), budburst has a higher chance of being uniform throughout the season. In regions with less defined season and where temperature changes gradually over time (as in maritime climates), budburst will be more staggered. This is, of course dependent on variety, as some varieties are innately early or late budders.
- SOIL FACT: Higher soil temperatures around the roots will promote early budburst. Dry, free-draining soils hold more warmth than sticky water-holding soils—a consideration for those planting in cooler climates and looking to improve the rate of ripening.
Budburst will fail if:
- It experiences frost. If there are unusually mild climates during winter dormancy, this can actually promote early budburst. No bueno if, following that early budburst, there are excessively cold, frosty conditions. Frost will damage buds.
- FARMING FACT: Winter pruning late during the winter dormancy phase can delay budburst and is a good technique for growers in areas where spring frost is a known hazard.
3. Shoot and Leaf Growth (March—July in N. Hemisphere; Sept.—Jan. in S. Hemisphere)
Defined as the time when shoots continue to grow and leaves as well as inflorescences begin to form.
What a vine needs:
- Those stored carbohydrates in the trunk, roots, and branches, accumulated from the previous growing season, are still being utilized for energy during the early part of the phase.
- As leaves form, they will begin to conduct photosynthesis and use that for its energy source. Thus, the vine also requires adequate amount of sunlight.
- Nutrients, namely Nitrogen, Potassium, and Phosphorus, are required at this time. It’s taken in from the soil via the roots, so soil health and trunk health are important during this phase.
Shoot and Leaf Growth will fail if:
- There are low stores of carbohydrate levels. This can happen if there was excessive leaf removal, water stress, mildew infections, or an extremely high crop load the previous vintage.
- It experiences too much water stress. Water stress can limit nutrient uptake, impede photosynthesis, and thus stunt shoot and leaf development.
4. Flowering and Fruit Set (May—June in N. Hemisphere; Nov.—Dec. in S. Hemisphere)
Flowering is defined as the opening of the individual flowers within an inflorescence. Fruit set is defined as the transition from flower to grape.
What a vine needs:
- Warm conditions—temperatures at or above 63°F—are required for flowering. Fruit set requires even warmer temperatures—between 79 and 90°F.
- Sunlight, warmth, water, and nutrients to aid in the development of compound buds (buds that will flower next vintage).
Flowering and fruit set will fail if:
- There are excessively cold, rainy, and/or windy conditions. If this occurs during pollination, there is an increase risk of millerandage (the formation of a grape bunch with several seedless grapes).
- There is excessively hot, dry, windy conditions that lead to water stress. Besides needing all those nutrients goodies for bud fruitfulness for the following season, excessive heat, dryness, and drought can lead to coulure (a condition in which fruit set has failed for a high number of flowers). NOTE: Excessive cold and cloudy conditions can also cause coulure and it’s noted that some of the more vigorous varieties (Cab Sauv, Grenache, Malbec, Merlot) are more susceptible.
6. Grape Development (June—Oct. in N. Hemisphere; Dec.—April in S. Hemisphere)
Defined as the period in which grapes accumulate sugar, acids, tannins, anthocyanins, and aroma precursors and compounds. It is broken into three phases: 1. Grape berry formation 2. Veraison 3. Ripening 4. Extra Ripening. I’ve talked about these phases in previous posts. For detailed explanations, please see Flowering and Fruit set and Ripening.
What a vine needs:
- Mild water stress during grape berry formation. This will speed up the formation process, which will in turn result in smaller grapes. That means lower overall yields, but more concentrated ration of skin to pulp.
Grape development will fail if:
- Too much water and nitrogen during grape berry formation. This will lead to excessive growth of green material, diverting resources away from the grape, delaying ripening. This may also cause the vine to enter what is called a “vegetative cycle,” where the diverted resources also effect bud fruitfulness for the following season.
- Cold weather and/or constant cloud overage during ripening. This will slow down photosynthesis and, thus sugar accumulation.
- Excessively hot and/or dry conditions. Extreme water stress will slow or stop photosynthesis and, thus, affect sugar accumulation.
- The level of sugar. This will directly correlate to the amount of alcohol in dry wines and affect the amount of sweetness in sweet wines.
- Aroma and flavor profiles. As grapes ripen, aromas and flavors evolve from under-ripe and herbaceous, to fresh fruit, to riper fruits, and finally jammy, cooked, or even dried fruits.
- Tannin ripeness. Skin tannins start out bitter and astringent and slowly soften during the ripening process.
How’d I do? Did I forget anything? Anything you want to add?
Thanks again for studying with me!
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