Capfall

The first year that we had flowering in our vineyard, I took many pictures of the process. I was so intrigued! Pictures are one thing but what is actually going on is quite remarkable.¹

• 3 to 4 days before bloom, the petals (calyptra) is easily detached from the flower
• Petals turn a pale yellow green
• The disks (discus) begins to swell
• On the morning of bloom, the rising temperature and the drying air desiccate the upper, less supplied part of the petals sticking together at their tips
• The tension developed between the outer, dry and inner, turgid cell layers first detaches one of the petals
• At 20- to 30-second intervals, the next petals separate
• The abscission (natural detachment portion) is helped by the swollen discs (lower and upper discs or nectaries)
• The filaments elongate, the petals separate from the base of the flower, to lift upward, thereby releasing the stamens
• Capfall, or the shedding of the calyptra has been achieved!

Reference:
1. M. Carmo Vasconcelos, Marc Greven, Chris S. Winefield, Mike C.T. Trought, and Victoria Raw1, The Flowering Process of Vitis vinifera: A Review, Am. J. Enol. Vitic. 60:4 (2009).