Dissertation on Multi-Year Thinning
by Rasmus Madsen
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Multi-Year Thinning Experiment
In our previous dissertation on thinning, we explored how the timing and intensity of thinning affect coffee tree physiology and coffee quality. Our findings revealed that the optimal benefits—balancing both quality and production—are achieved when thinning is performed at the onset of the seed maturation period (BBCH 75). At this stage, the green cherries are approximately 50% of their final size. This dissertation delves deeper into the multi-year effects of thinning. Specifically, we conducted annual thinning on Caturra coffee trees at the seed maturation stage from 2022 to 2025, consistently aiming for a Leaf Area Index (LAI) of 15.
From the tables, we clearly see the opposing reaction between reproductive and vegetative development. When the trees are too loaded with fruits (> 6 kg pr. tree), the yield in the following year is compromised due to suppressed vegetative growth and hence flower development. Conclusively, thinned is effective in mitigating biannual bearing.
An important observation is the cumulative yield is greater over a 4-year period when thinning is performed with this LAI of 15. The cumulative yield of thinned trees is 21,1 kg fruit pr. tree for versus 19,1 kg pr. tree for non-thinned trees. For a commercial coffee plantation with 4,000 trees per hectare, this would result in a yield increase of 8,000 kg of fruit per hectare. This is about 1,300 kg of green coffee, which is a significant increase. Therefore, we can also conclude that thinning increase yields over a 4-year period for the variety Caturra.
As proven in our earlier trials on thinning, the yield per tree is also clearly correlated with coffee quality – mentioned as cupping score in the tables. Therefore, we can confidently conclude that balancing yields will give a more stable high quality, which is of great importance for green coffee buyers that rely on stable quality.
Implementing the technique of thinning requires additional labor, but the financial returns from increased yields and improved coffee quality can more than offset these costs. Beyond the increase in yield, thinning enhances coffee quality, as evidenced by higher and more stable cupping scores. High-quality coffee commands premium prices in specialty markets, where buyers prioritize consistent quality. This added value can substantially increase the overall profitability of the harvest, particularly for high-yielding varieties. When the additional revenue from both increased yields and improved quality is considered, it often outweighs the labor costs associated with thinning.
Perspectives for Implementation
Thinning, or general crop load management, is not necessarily applicable for all coffee varieties. Low-yielding varieties naturally produce fewer cherries, so the competition for resources like nutrients, water, and energy is already reduced compared to high-yielding varieties. Thinning, which further reduces the crop load, may not result in significant quality improvements relative to the already limited yield. For this reason, we are focusing this technique towards high-yielding varieties.
Determining how much fruit to remove can be difficult. For this reason, we are working with the work-methodology called Leaf Area Index (LAI) as mentioned earlier. This index states are relationship between the leaf area and fruits mass (sources and sinks). We are typically working towards, depending on the variety, a LAI of 12-17. We start by measuring 10 representative trees for their leaf area and fruit mass to determine their LAI and the need for removal. To learn more about how to do this, reach out to info@pomacoffee.com.
In terms of labor, thinning can be done by manual labor, which is the most precise measure. However, labor shortages or high labor costs can make thinning economically challenging, especially in regions with limited agricultural workforce availability. With the current situation in most coffee producing countries, with high labor cost and shortages, we have to look for optimising practices. Therefore, we have developed a spraying combination of foliar nutrition that will burn off a certain amount of flowers, if thinning is to be done in the early stages, or a natural hormone product that will induce a temporary tree stress making the trees drop around 20% of the fruits on the trees, depending on the variety and yield, during the seed ripening stage. If you want to learn more about thinning in practice, please reach out to info@pomacoffee.com.
