Hmm... This question can mean at least three different things. In what geographic areas of the world do tea plants grow? Or it might reference the climatic conditions they require to grow. A more site-specific interpretation might ask what kinds of landscapes (hilly vs. flat) support these plants.
The different interpretations speak to the combination of factors that make each tea unique. It's never only its processing, or the soil, or where it grows, or the kind of plant, etc.
Let’s tackle the basics of each of the questions since they are interrelated. And the concepts from this page will be repeated throughout this website.
Tea plants can grow throughout a wide swath of the world, in a belt extending from about 42° North to 33° South. But the plants flourish, and most commercial tea production takes place, between 35° North in Japan to 8° South in Java—all tropical and subtropical regions.
The China bush is the hardier of the two main varieties of tea plants and thrives in the cooler parts of this range while the Assam bush does best in the warmer and more humid areas. Generally speaking, temperatures become cooler the further a site is from the equator. Not only does the distance from the sun decrease, but the length of the days also changes with latitude as does the presence of distinct seasons. All of these impact optimal growing conditions for tea.
Today the majority of tea is produced in China, India, Sri Lanka, Kenya, Indonesia, and Japan. Production in the continental United States is limited to a small pockets.
You would be correct to note that much of the U.S. lies within the potential latitude range for tea cultivation, yet it's not a large tea producer.
That brings climate factors into the picture. Regardless of whether it’s the China bush or Assam bush all tea plants need plenty of rainfall (at least 100" (254 cm.) annually), require well-drained soil, prefer a climate without extended periods of freezing weather in the winter, and don't tolerate drought well. Consider that even reputedly rainy Seattle receives only about 40" (102 cm.) of precipitation annually.
Growers rely on ample precipitation to develop the plants' foliage that ultimately is plucked for tea. Conversely they also require dry periods to harvest the leaves. On the whole, the plants thrive in a range between 70–90% humidity.
In terms of temperatures, tea plants are more tolerant of high temperatures than they are of cold. While they might be able to withstand frost, they typically don't produce well with any substantial period below the freezing point.
While Camellia sinensis can grow in many soils, it grows best in those that are rich, light, loose, and sandy. Young volcanic soil is ideal. Acidic soils are preferable, those with a pH between 4.4–5.5 are best (definition of pH). Soil type is one of the primary factors that contributes to a particular tea’s distinctive character.
Other factors that also influence tea cultivation are the presence of hills, mountain ranges, major bodies of water, and major weather phenomenon.
Hills can provide protection to a tea garden in an otherwise unfavorable environment—either protecting tea plants from harsh winds or giving them a favorable sun exposure. If you have a home garden, you may have taken advantage of this on a smaller scale by siting a tender plant on the south side of a building or sheltered from the prevailing winds.
Temperature decreases as elevation/altitude increases. So a mountain site that might otherwise be too warm has the potential to be suitable for tea. Moisture is important in tea cultivation as noted above, and tea gardens in mountainous locations can benefit from the fog that regularly settles in the valleys. Too high though, and the clouds might block out too much of the sunlight that plants need.
Oceans and other major bodies of water have a moderating effect on the local climate. This means that temperatures get neither as hot in the summer nor as cold in the winter as nearby inland locations. So places at higher latitudes near an ocean might be able to grow tea while an inland location at the same latitude could not.
Finally, the major weather phenomenon affecting tea cultivation is the monsoon. The monsoons bring rains that provide the moisture needed for lush tea plant growth, but they are also associated with the necessary dry periods when the tea leaves can be harvested and during which the plants can rest.
Tea gardens can be found on both hilly and flat terrain. As we hopscotch across the world, we'll see how sites vary among and even within individual countries.