It has grown in the wild there for ages and the natives there have taken kratom for thousands of years by simply picking and chewing on the kratom leaves. It has only recently become popular all of the world due to it's euphoric, pain relieving and sedative properties.
Some even call this the "new age herbal gold rush" due to the amount of attention it has gained in the recent years.
Many of the locals there actually make a living from cultivating their kratom crops, there of plantations all over. The farmers pick the leaves by hand and then wash and dry them by hanging them up.
Hand Picking Out of Harvest
Here's a short video that shows one of the kratom farms in Asia.