Veraison is the critical shift in the grapevine’s physiology from vegetative to reproductive growth, as the vine begins to dedicate its resources to maturing the fruit. This critical point is when all the “quality” goes into the fruit – sugars accumulate, acids change form, color develops, etc.
This season can be summarized as a late start, with a cooler beginning and then an extended hot spell. Some think that the hotter temperatures will help the fruit ripen, but the opposite is true. When temperatures soar, vines literally shut down (or “go into stasis”) to preserve energy. If the metabolism of the plant isn’t revving because the vine is partially shut down, then the fruit isn’t ripening. In addition, when the vine shuts down the leaves turn away from the sun, and the fruit is more exposed to sunburn.
Plant hormones and nutrient status play critical roles in veraison. Plant hormones trigger the shift in what nutrients the plant accumulates, what it translocates and where in the plant it delivers them. If the plant hormones are not fully “flipping the switch” for veraison, then resources that should have gone into maturing the fruit don’t get there, or they get there late in reduced quantities. Soil microbes produce plant growth regulators that the plant uses to make the transition into veraison more efficiently, lessening delays in building fruit maturity and quality.
Root exudation changes during veraison, as the vine prompts specific soil microbes to get them to provide specific nutrients and to produce the complex organic molecule building blocks the plant uses to develop color, flavor and aroma characteristics in the fruit.
MetaGrow ST, a soil microbial inoculant, is a quick and inexpensive way to restore soil microbiological functions for the vine and stimulate veraison. A good program to get the soil microbes functioning to support grape maturation and quality is to apply 4-5 gallons of MetaGrow ST/acre just before, during or shortly after veraison. Apply 2 gallons per acre every two weeks thereafter until after your post-harvest irrigation.
