Flowering/Fruit Set

Grapevine flowers are born in a cluster (or bunch).  The main axis of the cluster is called the rachis. When spring temperatures rise to 68F the flowers typically begin to bloom.  The time between budbreak and bloom is usually six to nine weeks, depending on the temperature.  Individual flowers of California table grapes are small, greenish and usually perfect – which means they have both male (stamens) and female parts (carpels).  The calyptra (or corolla) is a covering tissue for stamens and carpels and it is made of three to nine greenish petals firmly united at the tip.

When conditions are favorable, the flowers typically bloom for eight to ten days.

To the casual observer the opening of a grape flower may seem to be very different from that of most other flowers: the calyptra becomes detached at the base instead of separating at the tip. It is shed entirely, as a cap.  Immediately after blooming, the pollen sacs open and release pollen and pollination occurs.

Fertilization occurs 2-3 days after pollination.  The fruit set stage follows flowering almost immediately, when the fertilized flower begins to develop a seed and grape berry to protect the seed.  Most California table grape varieties are seedless – soon after fertilization the seed stops developing, resulting in seedless berries.  Grape berries pass through several growth stages from the time they are set until they are fully ripe.


Flowering Cluster Detail

Flowering Clusters

Stems and Carlpels

Opening of Grape Flowers

Opening of Grape Flowers

Vineyard Appearance During Flowering

Fruit Set

Fruit Set

Early Basal Leaf Removal