Why height slows the leaf
Tea grows more slowly as it gets colder, and temperature drops roughly 0.6°C for every 100 m of ascent.
A garden at 1,000 m in the same county as one at 300 m will pick later in the spring and flush fewer times across the season.
Slower growth gives the leaf more time to build amino acids, and it keeps the catechins that make a green tea bitter from running ahead of them.
Cloud is the other half. High gardens spend more of the morning in mist, which cuts direct sun and shifts the leaf towards the same softer balance.
This is the mechanism behind the whole idea of mountain tea, and it is real.
What is not real is the assumption that height automatically produces a better cup.
A slow leaf is simply a leaf with more time, and time is the only thing elevation genuinely buys.
Everything else credited to it, from soil to mist to some notion of mountain energy, is either secondary or invented.
Growers know this, which is why the ones on good high plots talk about their picking standard rather than their altitude.
What changes in the cup
The practical difference is usually sweetness against bite.
High-grown green tea tends to hold a rounder, thicker mouthfeel and to stand up to hotter water without turning harsh.
Low-grown same-cultivar leaf from the same county is often more aromatic and more astringent, and it punishes over-steeping faster.
Neither is wrong. They suit different water and different habits.
The catch is that the difference is smaller than the price gap suggests.
A well-made low garden and a careless high one are easy to tell apart, and the garden height is not what separates them.
Plucking standard separates them, and so does how quickly the leaf reached a pan after being picked.
Leaf that sat warm in a basket for hours has already begun to change, and no elevation recovers it.
Firing matters just as much, since a pan that is too cool leaves the leaf grassy no matter where it grew.
Ask a seller about those two steps rather than about the mountain, because those are the answers that actually predict the cup.
Where the high gardens are
In China the genuinely high green tea gardens are in the south and west rather than in the famous east.
Emei in Sichuan runs its tea up past 1,200 m, and Zhuyeqing（竹叶青）is picked from those slopes.
Parts of Guizhou, including the hills around Duyun, sit high and wet and produce soft leaf that rarely carries a famous name.
Lushan（庐山）in Jiangxi grows its cloud tea between roughly 800 m and 1,000 m.
By contrast most of the famous eastern regions are low. Longjing（龙井）hills sit around 100 m to 300 m, and Biluochun（碧螺春）is grown almost at lake level.
Those teas are famous for craft and for history, not for height, and pretending otherwise is how the term gets abused.
Height also costs the grower, because steep plots cannot be mechanised and everything on them moves by hand.
Frost is the other risk, and a late one on a high plot can remove a whole first flush in a single night.
Lower gardens lose less to weather and pick more often, which is most of why they supply the bulk of the market.
When height is not the answer
A high-grown label is one of the easiest things in tea to put on a bag and one of the hardest to check.
There is no agreed altitude at which a garden becomes high grown, so the word means whatever the seller wants.
If the listing gives a number, treat it as a claim worth one question: which mountain.
If it gives no number, assume the tea is ordinary.
Height also does nothing about freshness, which matters more than elevation for a green tea by a wide margin.
Last spring’s mountain leaf kept badly will lose to this spring’s valley leaf kept well, every time and usually by a distance.
Buy high-grown leaf if you like the softer profile and you trust the seller. Do not buy it as insurance against bad tea.
The word to watch is alpine, which has no agreed meaning in Chinese tea and turns up mostly on export listings aimed at buyers who will not ask.