| Lynsey Harley

Coffee flowering

Generally, coffee trees in the northern hemisphere will flower mostly in the northern hemisphere spring, while trees in the southern hemisphere will do so in the southern springtime. Trees on the equator can have two flowering peak periods per year.

The coffee tree is a living being, and when it is exposed to any kind of stress that threatens its existence, its immediate reaction is to reproduce to preserve its genes.

In countries with a well-established long dry season, e.g. Brazil, the long multimonth winter dry spell will ‘water-stress’ the coffee trees. Once the rains return, the coffee trees flower extremely strongly.

Almost all of the available productive nodes will fill up with flowers in full rosettas. This is why countries like Brazil only have one strong crop peak per year. In countries where the dry season is not pronounced or extensive, the flowering can occur in rounds. Every time there is a dry period, the following showers only trigger flowering in part of the available space, and the remaining space can be filled with flowers triggered some weeks or months later. Because one tree can be presenting cherries at different stages of maturity, this necessitates hand-picking, to select only the ripe cherries.

Although the return of the rains after a long dry spell will trigger flowering, it is the ‘back-up’ rains that follow the flowering that are probably most important in guaranteeing a large crop for farmers. If flowers are triggered, but a long dry period follows, these flowers will be aborted, and those productive nodes cannot be used again. The tree, and the farmers, must wait until new productive nodes are grown. In contrast, if there are constant rains in a country, as well as negatively affecting photosynthesis and the spread of disease, it can cause havoc with the flowering function of the coffee tree, as there is no dry spell to build up water stress.

Around ten days after rains break a dry spell, the coffee tree should flower. Robusta depends on cross pollination which happens after the flower opens. Arabica on the other hand self-pollinates, mostly before the flower opens. After a month, pinhead cherries are seen. It then takes another seven months for the coffee cherry to grow and ripen, changing from green to deep red (sometimes yellow). The ripe cherries can now be harvested, and then processed to remove the pulp, mucilage and parchment to reveal the one or two seeds, i.e. raw coffee beans, within.

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