Shade preference in Coffea arabica varies among genetic groups, with significant differences observed between both traditional lineages and modern hybrids. Typica-derived varieties (i.e. Gesha) exhibit a strong preference for shaded environments. In contrast, Bourbon-derived varieties (i.e. Caturra), while still preferring shaded environments, demonstrate a higher capacity to withstand increased light exposure, often performing better in systems with moderate shade levels. Modern hybrids, particularly those incorporating C. canephora genetics (e.g., Catimor and Sarchimor), tolerate full-sun cultivation even better. While most C. arabica benefit from some level of shade, the degree of preference varies based on genetic background.
Figure 1 – Gesha, a Typica-derived variety, produces the best quality and yields in very shaded conditions.
Figure 2 – Caturra, a Bourbon-derived variety, produces the best quality and yields in moderately shaded conditions.
So, coffee trees require adequate sunlight to produce photosynthates via photosynthesis, sustaining their vitality and productivity. However, excessive sunlight and heat can stress the trees, rendering them unproductive due to their shade-requirements. Therefore, it’s essential to strike a balance between sunlight and shade to promote both productivity and quality across different varieties, each with unique requirements. This can be difficult to manage with shade trees as they change over time and do not offer uniform shade across a field. This underlines the importance of flexibility in the production system to manage shade effectively. For this reason, we are utilizing the shading properties of kaolin clay formulated with an adjuvant, which can be utilized in different concentrations and sprayed directly on the leaves to simulate various levels of shade. This method allows us to provide different varieties with optimal shade conditions to thrive, even under zero natural shade conditions, to fit their variety specific requirements.
The kaolin clay creates a thin film that covers the leaves, which reflects parts of the sunlight – also excessive infrared and ultraviolet radiation. This reflection lowers the leaf temperature significantly (by up to 3.5℃), reducing the sun- and heat stress experienced by the plants in clear warm spells. The reduced stress promotes stomatal activity, increasing photosynthesis and hence yield and quality.
Simultaneously, the lower leaf temperatures also mean a longer ripening period. Our in-field trials have shown alterations to the ripening period by 2-4 weeks. This extension allows for better biochemical fulfillment of the seeds and fruit, ultimately leading to a higher density and greater cup quality. It also helps lower water loss through transpiration. This is particularly beneficial in dry or arid conditions, as it allows the trees to conserve water for essential plant processes and avoid drought stress.
In Practice
Kaolin clay must be sprayed directly onto trees to cover the leaves, fruits, and branches. This can be done using either a backpack sprayer or a vehicle-mounted sprayer. The concentration of the spray mixture for established trees can range from 10–30 kg of kaolin clay mixed with 200 liters of water per hectare (5–15% concentration), depending on the desired level of shade. The adjuvant in the product ensures that the kaolin clay adheres to the trees, even after heavy rainfall. As a result, only three applications are typically needed for full-season coverage.
A key advantage of this product is that it is chemically inert, meaning it can be safely mixed with foliar nutrients, fungicides, and insecticides without causing toxicity issues. However, we always recommend preparing a small test mixture beforehand to ensure compatibility before applying it in the field.
One important factor to consider is precipitation in the spray tank. Kaolin clay tends to settle at the bottom of the tank during spraying, making agitation essential. This can be achieved in several ways—such as adding agitation magnets to the tank, pausing periodically to shake the tank, or preparing smaller batches of the mixture at a time. If the clay remains well suspended, you will see an even white coating on the trees. If not, the trees sprayed first will appear whiter than those sprayed later. Additionally, keep in mind that it takes about 15 minutes for the trees to dry before the white coating becomes clearly visible.
Young Plants
Newly planted trees have a shallow root system and a small leaf area, making them highly vulnerable to abiotic stresses. As a result, coffee trees typically take a long time to reach full production and establish themselves, often leading to significant losses both in terms of productivity and trees along the way. However, the use of kaolin clay gives these young trees a much better start by optimizing photosynthesis, water-use efficiency, and reducing sun and heat stress. The results are lesser replanting, earlier production and better quality.
Figure 3 – A young coffee plant 2-months after the application of the kaolin clay. The older dark leaves were treated, and the brighter young leaves have emerged since the application, showing a very fast growth rate.
Concluding remarks
As global temperatures rise and weather patterns become more unpredictable, the ability to flexibly control shade levels may become a key strategy for maintaining both yield and quality in coffee farming. In conclusion, kaolin clay offers a highly effective, flexible, and sustainable solution for managing light exposure in coffee farming. While proper handling and application techniques are essential, its benefits in enhancing growth, quality, and resilience make it a valuable and sustainable tool for the future of coffee production.
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