Know your vines #5: The value of understanding fruit set

Know your vines #5: The value of understanding fruit set 2000 1333 Sectormentor

In our Know your Vines blog series we will share practical tips on which metrics to monitor in your vineyard. This is the fifth instalment, stay tuned for more as the coming seasons unfold!

“If you can’t measure it, you can’t improve it.”

The value of knowing % Fruit Set

After the buds have burst, flowering is over (or almost over)…the caps are off and the grapes are beginning to form – we are well and truly into another season and the countdown to harvest has begun, yet again! In this post, we wanted to tell you a bit about % fruit set and why this a useful metric. If you did an inflorescence count prior to flowering then it’s very easy to determine what % of your inflorescences have “set” fruit.

Photo: Vines just finished flowering – fruit set just starting…


Fruit set is vital in the phenological progression of the vine, as it is the moment that the fruit actually comes into being -it’s the first indicator of how abundant (or not) the harvest might be. Knowing the % fruit set helps you to know if the vine is out of balance or if something went wrong at this point and you need to do things differently in future years.

Of course, a key factor that affects fruit set is outside of our control – the weather! High winds and heavy rain (or worse, frost), can really damage flowers’ ability to turn into fruit. But poor management decisions, as well as reduced vine health, can also impact fruit set – so this is an indicator to learn how to learn from!

“We monitor fruit set to make sure we are managing the vineyard as effectively as possible. You have to be very careful during flowering, especially with any sprays, it can be very delicate and you can cause poor fruit set. So we always check % fruit set to learn and improve our management in following years.” – Joel Jorgensen

Poor fruit set in vines can be due to carbohydrate supply, water supply and mineral imbalance. Here is a nice description of how and why from a US vineyard outreach officer:

‘Deficiencies of any of the essential mineral nutrients (e.g Zinc, Boron) can affect fruit set detrimentally.  Unbalanced C:N status of the vine can also result in poor flower development and fruit set. Overly vigorous (lower C:N ratio) or weak vines (higher C:N ratio) with insufficient or in-efficient leaf area (e.g. due to herbicide damage, insect feeding, disease attack)  tend to have reduced fruit set and loose clusters.’ (Reference)

Different varieties can also be more or less likely to set all their fruit, so starting to understand different varietal and block behaviours with fruit set helps to build up a picture of those vines over time and optimise vineyard management based on the expected fruit set. This also means you can pay special attention to any areas of the vineyard that are particularly susceptible at flowering:

“Flower set is dependent on the weather but some varieties are more prone to poor fruit set in certain conditions. When we count inflorescences, we assume 100% fruit set. In August when we count bunches post flowering we then update the yield prediction. And also determine the % fruit set so we can manage the blocks accordingly going foward.” – Will Davenport, Davenport Vineyards.

How to calculate fruit set?

Go out and do an inflorescence count as the flowers come into bloom. Then sometime after flowering is all finished, and the caps have blown off, go out and count the number of bunches. ‘No. of bunches’ divided by the ‘No. of inflorescences’ will give you the % fruit set. Using Sectormentor makes this easy:

Monitoring with Sectormentor:
Sectormentor makes it easy to record flower / inflorescence counts and bunch counts at the touch of a button on your phone out in the vineyard. All the information you record is then available as soon as you get back to the office. You can easily see the % fruit set for each block, and this is recorded year on year, so you can start to build up a picture of each block and how the fruit sets for that specific clone, variety, location. This is about really knowing your vines!


Check out 10 key metrics to monitor in your vineyard and find out how our app Sectormentor helps you record data & manage your vines to build ecology, profitability and beauty for your vineyard.