Very vigorous grapevines tend to produce extremely long shoots during the first years. However, such strong growth comes at the cost of the fruit - often the flower buds fail to develop (Image 01), dry up before flowering (Image 02) and end up dropping off. By pinching back the shoot tips before flowering (Image 03), the sap flow is "dammed up," resulting in better flower development and pollination. However, even after flowering, some susceptible varieties - especially after wet and cold weather - can suffer the dreaded "coulure" or "shatter," whereby fruit will fail to set and fall off or "drizzle down" (Image 05).
However, pinching back shoot tips does have its problems: once you start to pinch back or trim shoot tips on a very vigorous vine, you will be required to carry out Summer Pruning once or several times.
- Image 02: Stunted inflorescence on a young, too vigorous shoot.
- Image 04: During the actual flowering period it is essential to leave the vine alone. Wet and cold weather during this time will cause severe "shatter" in some susceptible varieties (esp. susceptible to wind), and grapes will not set properly, a damage which will be irreparable for that year.
- Image 03: Pinching back shoot tips before the flowering period can promote flower development.
- Image 05: It is quite normal for flowers to drop off during and shortly after the flowering period, about 80% of all fertilised flowers are shed. For varieties with very large berries such as "Theresa", it is particularly important that only a small number of berries develop, because too many berries will cause them to press against each other.