What the plant needs
Tea grows where it is warm, wet and humid, and where the wet is spread through the year rather than delivered in one burst. Total rainfall matters less than distribution: a region with generous annual rainfall concentrated into three months has a long dry period during which the plant stops, and the plant experiences that as drought regardless of the annual figure. Humidity matters independently, because a hot dry wind takes water out of a leaf faster than roots can replace it even in moist soil. Those requirements — warm, evenly wet, humid, acid, free-draining, frost-limited — describe a fairly narrow band of the world. Within that band there is more variation than the description suggests. Assam is hot, low and drenched by monsoon; the Sri Lankan high country is cool, misty and wet on a different schedule; Kenya sits on the equator at altitude with two rainy seasons; Shizuoka has a genuine winter. The plant tolerates all of them, and what it does in each is different enough that the resulting teas share little beyond the species.
Growth stops below a threshold
Shoot growth slows as temperature falls and effectively stops somewhere in the low teens Celsius, with the exact point depending on the plant. Above that, growth rate rises with temperature up to a point and then falls away again as heat becomes a stress. This is why the same cultivar produces a shoot in a week in an Assam summer and takes a month at altitude in early spring, and why regional harvest calendars are so different that they barely look like the same crop. Heat stress at the other end is a real limit rather than a theoretical one. Above a certain point the plant closes down to conserve water, shoot growth slows even with moisture available, and prolonged high temperatures with low humidity cause scorching on exposed foliage. This is one of the mechanisms behind interest in shade in hot origins, and one of the reasons the same cultivar behaves differently in a hot year and a mild one.
Dormancy, and why it concentrates quality
In regions with a real cold season the plant shuts down for months. During that period it is not building shoots, and reserves accumulate in root and stem. When temperatures rise, the first growth of the year draws on those reserves, and the shoots that result are the ones that Chinese, Japanese, Darjeeling and Korean producers price highest — pre-Qingming greens, shincha, first flush, ujeon. The mechanism is straightforward: a long accumulation period feeding a small amount of new growth. It also explains why those teas are limited in quantity in a way that no amount of demand can change. The dormant period does other work as well. It is when pruning is done, because a plant that is not growing can afford to lose its frame; it suppresses pest and disease populations that cannot overwinter; and it gives an estate a predictable annual window for maintenance, replanting and repair. A region without a winter has none of those, and has to fit all of it around continuous production.
The flush structure of a seasonal region
Where there is dormancy, the year has a shape. Darjeeling’s first flush is the light, green, brisk spring picking; its second flush after the early monsoon rains is the fuller muscatel style; the monsoon flush is high-volume and low-value; and the autumn flush gives a rounder, softer tea before the plant shuts down again. Assam’s own two-flush structure is similar in outline and completely different in character. These are not marketing categories layered onto a continuous crop — they are genuinely different material, produced under different conditions, months apart. China’s calendar is organised on the same principle with different landmarks, keyed to the solar terms: tea picked before Qingming, then before Guyu, then later. Those are dates rather than qualities, and their significance is that they mark how far into the spring flush the picking happened. Japan’s ichibancha, nibancha and sanbancha do the same job by numbering the flushes outright.
Year-round production near the equator
In Kenya, in much of Sri Lanka’s low country, in Malawi and in Indonesia, there is no dormancy to speak of and plucking runs all year. That is an enormous commercial advantage — a factory can run continuously, cash flow is steady, and there is no seasonal labour peak — and it comes with the corresponding limitation, which is that no picking is special. Equatorial origins still have seasonal variation, driven by rain rather than by cold, and Kenyan tea does have recognised better periods. What they do not have is a spring, and the entire vocabulary of first flush and pre-festival picking does not apply. The advantage is larger than it first appears because it compounds. Continuous production means a factory’s capital is working all year rather than for a few months, which lowers unit cost; it means a permanent rather than seasonal workforce, which changes the labour relationship entirely; and it means supply that a large buyer can contract against reliably. Those are the conditions a commodity market is built on.
What this means for a buyer
It tells you which claims are meaningful for which origin. A harvest date is highly informative for a Chinese green tea or a Darjeeling and nearly meaningless for a Kenyan CTC. Freshness matters intensely for a seasonal spring tea and much less for a year-round black tea blended across months. And a region’s climate largely determines what it can sell into: a region without dormancy is structurally pushed towards volume markets, which is a constraint that no amount of quality ambition on the ground can fully escape. It also tells you what to worry about. For a seasonal origin, the risk is a single bad fortnight — a late frost, a drought at bud break, hail during the flush — removing the most valuable crop of the year. For a year-round origin, the risk is a shift in the rainfall pattern that affects the whole twelve months. Those call for different responses, and conflating them is why generalised statements about climate and tea tend to be unhelpful.