August 11, 2021

Why do coffee plants flower & what does it mean for producers?

The blooming of white, fragrant flowers on coffee plants is the first step of a year-long journey. When their crops flower, farmers can start to determine potential productivity for that season, as the flowering nodes will subsequently develop into coffee fruits. Effectively, the more nodes and flowers that grow, the more cherries a farmer can harvest.

Blooming seasons across the globe vary due to climate, but the timely occurrence of rainfall is a key stage in the seasonal life cycle of the coffee plant. However, thanks to increasing temperatures, unpredictable droughts, and erratic rainfall patterns, predicting the flowering season is becoming more of a challenge for producers.

To learn more about the connection between flowering and coffee productivity, I spoke with two coffee researchers based in Brazil. Read on to find out what they said.

You may also like our article on how grafting arabica to robusta can improve coffee yields

coffee blossoms

Coffee flower blooming explained

Coffee trees start to flower an average of three to four years after planting, with the flowering phase lasting for approximately two to three months. Each flowering bud can develop up to four flowers, which grow in clusters along the axis (stem) of the leaves; when they bloom, they have a rich jasmine-like scent.

Understandably, the flowering phase is vastly different from species to species. For instance, while arabica plants can self-pollinate, robusta plants rely on cross-pollination in order to grow. Robusta flowers also tend to be bigger and grow in larger quantities (around eight to 20 per axis, compared to two to 12 for arabica).

For flowers to grow, the plants first need heavy rain. A couple of weeks after the first rains of the season, the buds along the trees will start to flower. In most cases, workers will leave the farms at this point, as flowering is a very delicate process and the plants should remain undisturbed for optimum growth.

About four weeks later, the scent of the flowers reaches its strongest in the “peak” of the flowering season. This is often considered something to celebrate among farming regions, as it only lasts for around three days before the flowers begin to fall to the ground. It is also a sign that the cherries are starting to develop. 

Some couples in coffee-producing communities even plan weddings at this time to capture the scarce beauty and rich aroma of the fields of white flowers.

After the flowers fall to the ground, they leave behind a small round nub known as a “carpel”, which then grows into a cherry over the next few months.

Sérgio Parreiras Pereira is a scientific researcher and Doctor of Agronomy at the Instituto Agronômico De Campinas (IAC). He says that the carpels expand until they reach maximum size. This is when the ripening process begins.

Coffee fruit is produced in the new tissue formed in these carpels, so the flowers themselves can actually be harvested without affecting the growth of the fruit. In some cases, farmers have even used coffee flowers to diversify their incomes, as they can be used to produce tea and other beverages, such as kombucha

bee on coffee blossoms

Why is uniform blooming important?

“Uniform blossoms mean a uniform ripening will take place,” Sérgio explains. “This results in higher-quality cherries.” 

However, in order for uniform blooming to occur, rainfall must be consistent and predictable. At present, rainfall patterns in coffee-growing countries are becoming more erratic, largely because of climate change. 

Higher temperatures allow the Earth’s atmosphere to retain more moisture, which leads to heavier rainfall, but this rainfall isn’t evenly dispersed across the planet.

With more erratic rainfall, irregular blossoming patterns may occur. Flowers from the same trees or branches can be pollinated at different times, leading to varying levels of maturation. Consistently heavy rainfall or storm weather can even damage the plant.

Consistency on the same plant is important. If producers have ripe and unripe – or healthy and damaged – fruits on the same branch, they would need to harvest them at different times. The producer would have no option but to pick the cherries by hand, a process that requires more time and labour.

However, in some regions, hand picking coffee cherries has become synonymous with a focus on quality, as it has the potential to guarantee better consistency.

José Donizeti Alves is a professor of agronomic engineering and plant and molecular physiology of coffee at the Federal University of Lavras (UFLA). He tells me that unfortunately, erratic rainfall patterns and temperature fluctuation will continue to happen in the future because of climate change, and will likely only become more damaging.

Just like rainfall, temperature is an essential factor for coffee plant growth. Scientists agree that mild temperatures between 19 and 24º C (68 to 75.2ºF) are perfect for initiating the flowering process, no matter the location of a coffee farm.

But with average global temperatures steadily increasing, the flowering phase may become less uniform and more difficult to predict. This makes harvests harder (and subsequently more expensive) to organise.

When temperatures become too hot for farmers to grow coffee, they often respond by “climbing” to higher altitudes with lower temperature ranges, but this also comes with its own set of issues. Higher altitudes typically mean steeper and more rugged terrain, which means there is less space to grow coffee and that it becomes more difficult to harvest it.

coffee farm irrigation

Irrigation & flowering

Natural rainfall in adequate quantities is the “preferred form of moisture” for coffee plants, according to Sérgio. Not only does it initiate the flowering process, it also allows the plant’s roots to absorb nutrients and minerals from the soil.

However, to ensure that coffee plants are suitably watered and nourished through the harvest season, no matter how consistent the rainfall is, many farmers have instead chosen to use irrigation.

Traditional irrigation methods

The “standard” water systems used to irrigate coffee usually use one of three methods: 

  • Surface/”flood” irrigation: Where water is distributed across the surface of the soil using gravity (flowing from the top to the bottom of the farm, for instance)
  • Localised irrigation: Applying water only to the soil directly surrounding each plant
  • Sprinkler irrigation: Irrigating crops using rows of powered sprinklers that are placed above or among the crops 

Controlled water stress

In recent years, coffee producers have started to experiment with a newer irrigation method, known as “controlled water stress”.

The process involves restricting the irrigation of the plants to create more uniform flowering. The method has grown in popularity over the last decade.

By suspending irrigation for a long time (up to two months), farmers can control flowering when it resumes. In turn, this means that cherries develop in a more uniform manner, therefore increasing the consistency and quality of harvestable coffee.

According to research conducted by Embrapa, this irrigation process is effective when carried out properly, and can support producers to get the most consistent results from their trees.

Studies published by the institution show that coffee trees subjected to controlled water stress not only flowered and developed fruit in a more uniform manner, “but also presented themselves in better conditions for the next harvest”. The productivity index for some surveyed farms increased by as much as 15%.

bee on coffee blossoms

Best practices for uniform farming

Ultimately, both José and Sérgio tell me that guaranteeing an even blooming phase is possible, even through unpredictable rainfall and extreme temperature fluctuations.

However, it’s also important for producers to realise that when the plants do receive water (by irrigation or rainfall) earlier in the season than they should, it can increase the likelihood of certain diseases.

José tells me: “Climatic circumstances must be favourable for fungi (such as coffee leaf rust) to attack plants. If rain arrives before scheduled, it has a higher chance of triggering them.”

However, he says that fungicides can be used to prevent these diseases, and certain climatic factors can even be used to help to fight them off – including farm temperature.

José says that among the international coffee science community, extreme care with macro and micronutrition, the control of pests, diseases, and weeds, and bioregulator use are currently recommended best practices for productive, uniform flowering. 

“[These] are normally compromised by drought and heat,” he says. “They can then inhibit the synthesis of growth inhibitors in the post-stress period.”

For more information on how to mitigate unpredictable rainfall patterns and how to use irrigation methods effectively, Sérgio recommends seeking advice from official agronomy projects and relevant coffee research organisations in your country.

coffee tree in bloom

Although the harvest itself might be the most profitable step for farmers, the blooming of coffee plants’ white, jasmine-scented flowers is an important milestone in the cycle of coffee production.

With the consequences of climate change already forcing farmers to develop more advanced methods of irrigation, an understanding of the relationship between uniform blooming and farm productivity is vital for coffee producers.

Enjoyed this? Then read our article on a Brazilian roastery’s coffee flower kombucha.

Photo credits: Ibiporá Farm, Renata Silva

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