The following information was adapted from the FAO – Food and Agriculture Organization of the United Nations. Most of the content and all of the graphics can be found on their website
During the first few years a coffee tree makes many branches. In this growing phase it uses the majority of the nourishment it pulls in to make wood. When it is ready for first harvest that nourishment begins to direct a small amount towards yielding berries but most nutrients are used to continue to fuel the growing of branches. If the branches continue to outpace the growing of berries the tree will not develop in a way to maximize yield. Also, the Robusta trees in Hainan can grow up to 12 meters tall. Since very few farmers are larger than 1.75 meters tall you can imagine how hard it would be for 5’8” farmer to harvest from a 40’ high tree. Pruning is not easy but it is necessary.
Robusta trees have several main stems that grow from the trunk. In order to prune the tree to maximize growth you need to spread the main stems so that several may grow. The most common way to do this is to bend the first stem down and tie it to a stake. That will enable a couple more shoots to grow out of the trunk.
Since the wood of a branch has berries for only one harvest year you will want to cut off the bent stem after it sprouts its first year of cherries. A new stem will grow in its place. For the stems that will subsequently grow you will want to cut down the branches after the next two years of harvest. The fruit will only grow on the tips of the branches so by cutting these back you are directing more nutrients to the cherries and less to the wood. After those first two phases of pruning you will allow the stems to grow for the next three to five years. It is recommended that you only cut one stem per year (for example, if you have three stems you cut one at year three, the next, at year four, and the following at year 5). You will continue this cycle until the tree reaches about 18 years old. At that age the production begins to diminish and you will eventually need to replace.
The reason the cherries only grow on the tip of the branches is because each part of the branch can only bear fruit one harvest year. The next year, that part of the branch bears no fruit. The berries grow on the new wood of the branch which has grown during the year. A branch will yield fruit for several years but it is always a different part of the branch that bears fruit.
Since the tree’s natural proclivity is to produce wood it will sometimes produce a branch that grows upward out of a main stem. This is called a sucker. You will want to cut away the suckers because they suck away nutrients but never bear fruit.
If a tree is not yielding many berries on a particular main stem you will want to cut it back. If severe loss of yield is happening you will want to leave only one main stem on the tree and cut off all the others. If the tree is healthy new stems will grow in place of the ones you cut off. As soon as those begin to grow you can then off the remaining old stem and that one will regrow as well.