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As spring unfolds its vibrant colors across the various landscapes that Napa Valley has, a magical transformation is taking place in some of the vineyards. Our fertile soils of the Rutherford Dust Vineyards on the valley floor are signaling the start of the next phase of the winegrowing season.
Bloom (also known as flowering) and fruit set is another important phase in the grape growing season right after bud push or bud break. At Neal Vineyards, we have finished our cluster counts, and now bloom will determine the number of berries in each grape cluster. Currently, our white varieties in Rutherford are in pollination. Melon is leading the way with Fiano, Albariño and Vermentino following. Once bloom is completed and “berry set” or “fruit set” is prominent grape growers can calculate fruit loads and begin to plan for harvest. Berry set is the completion of bloom or pollination.
Flowering generally occurs about a month to six weeks after bud break. This varies year to year depending on mother nature’s temperatures during this period. Cooler weather will lengthen the time and heat will reduce. The flower clusters are called inflorescence and emit a lovely fragrance that envelops the entire vineyard in sweet aromas. Honeybees do visit the vineyard but not for grape pollination they are out working the cover crops. Bees are not essential to the grape pollination process since cultivated grapevines are hermaphroditic, possessing both female ovaries and male stamens or self-pollinating.
During bloom, the delicate grape flowers are very vulnerable to damage from heavy winds, rains (and I even saw hail at this time of the year in the past) or an unexpected late frost. The last big loss by heavy rain during bloom was in 2015, however, not as big as 2011 in Napa Valley where it cut the crop in half with a poor berry set. Like other times of the year Mother Nature has its pros and cons with farming, which is one of our biggest risk factors. Vineyard managers can do everything they can to ensure an even and abundant fruit set occurs such as correct pruning and ensuring storage of carbohydrates from the previous year.
Currently, Howell Mountain is experiencing low temperatures in the early mornings. There are two common frost protection methods done in Napa Valley. Wind machines, which are used to pull warmer air downward and circulate it with the cooler air on the vineyard floor. The other, adding water through sprinkler systems. This was developed in the late 1960’s. Sprinklers must be turn on long well before freezing like 35 but it depends on dew point. The added water will freeze around the buds or shoots as temps drop to freezing or below. Sprinklers must also defrost the ice buildup when temperatures rise usually after sun rise. Sprinklers can be turned off after all ice is melted.
This spring Howell Mountain has seen a low of 27 degrees. This was successful by either method due to the dew point being high right after a week of rainfall. Hopefully, we will be getting past the frost threat of this season soon as it makes for a long day for farmers.
Other areas causing poor flowering can be low carbohydrates. The natural storage of carbohydrates from the prior year is very important. Another can be water stress due to drought(s) and can contribute to inflorescence necrosis. This is where part of the entire flower cluster is damaged which we would call a “poor set” referring to berry set. As you can imagine, losing part or entire flower clusters can be detrimental loss. But both are related mostly to mother nature, a farmer can add to the loss if farming practices are correct.
Loss of the flowers within the inflorescence is called flower necrosis or poor berry set will result in grape clusters that have varied of number of berries on the cluster. Delaying of bloom due to cool weather that elongates the time of bloom and this could a phase called hens and chicks. Hens and chicks describe both big and small berries growing in a single grape cluster. A little lost where pollination was interrupted during bloom isn’t always such a bad outcome and can contribute to better cluster ripening as it allows air can flow and more sun light between the berries.
High nitrogen levels in the vineyard soil can also affect the fruit set. Typically, this would be caused by farming with a heavy fertilizer program the year before. It is all about keeping vine balance with the current soils and knowing where the soils change within the row and area of the block. Rainfall totals for the season, the use of cover crops, balance pruning levels and in most cases, what a grower does the prior year affects the fruit and fruit set the following year. Planting nitrogen-rich cover crops in a vineyard that is deficient will help balance the levels and can promote a better fruit set than in those vineyards where nothing is done. Best practice is to monitor the nitrogen and other nutrients levels through petiole samples during bloom from the previous year. This allows a farmer to make intelligent decisions about farming practices with fertilizer types to add during the growing season and or the type of cover crops for the fall.
“We use certified organic materials when it comes to our compost and our fertilizer programs. Our compost is generated from our winery garden and livestock materials.” – Mark Neal, Neal Vineyards
About 10-14 days after full bloom the fruit set should be well established, and the pollinated flowers have disappeared or fallen. If they do not fall off that means the stuck to the forming berry which will cause other issues. What will be visual will be very small green berries that will eventually grow into individual grapes. At this time vineyard managers can begin to do crop estimates based percentage of an estimate of berry set for the block by looking at several clusters. While significant weather events can still affect the season, fruit set is the first indicator of how abundant (or not) harvest may be.
During the entire growing phase, vineyard managers make numerous decisions impacting the grapes: how to trellis or prune the vines, how to protect them from frost, hail, or heat, as well as from intruders in the vineyard (bugs, birds and the likes), care for the soils for the future vintages and ripen the grapes of this vintage. Mother Nature calls the shots, and we must learn to pivot and adapt to care for the grapes. After all, great wine is made in the vineyards.