The effect
Altitude matters in dark tea, but it matters for a reason most buyers do not expect.
The effect is not on how the tea tastes young, it is on whether it has anything to age into.
Yunnan’s pu-erh districts sit mostly between 1,200 and 1,800 m, and that band is not an accident.
Leaf grown there is dense and slow grown, and it carries the material that fermentation works on.
Low grown leaf from the same province is thinner, and it ages into something flat and disappointing.
Most of the famous mountain names sit in the upper part of that band, which is part of why they cost more.
Anhua in Hunan is much lower, and its tea is not meant to be aged in the same way at all.
Liubao in Guangxi is lower again, and the basket it is stored in contributes more than the garden does.
So the effect is strong for one technology and weak for the other two.
Where it is strong, it is a statement about potential rather than about immediate flavour.
A young high grown raw cake is often harsh, and the height is invisible until the tea has settled.
That delay is what makes altitude so easy to sell and so hard to check.
Why it happens
Slow growth is the core mechanism, and it works through what the leaf stores.
Cool mountain air stretches the growing season, and the leaf builds soluble material rather than bulk.
Fermentation needs that material, since wo dui（渥堆）and decades of ageing both consume the leaf.
Thin leaf has nothing to give, and no amount of processing manufactures it afterwards.
Day night swing preserves what the bush made, which is the same mechanism as in other categories.
Cloud cover softens the light and slows growth further, and the two effects reinforce each other.
Old gardens on thin rocky soil add a further constraint, and the bushes there grow slowly for decades.
Tree age and elevation are tangled together in Yunnan, and it is hard to separate their contributions.
Drainage on steep slopes keeps the roots healthy, which matters over a century more than over a season.
Microbial load is the local part, since each region carries its own population of organisms.
That is why moving the method elsewhere does not reproduce the result.
Slow growth, old roots and a local microbial population all point the same way.
Limits of the rule
The first limit is that altitude is a proxy, and the trade sells it as if it were a cause.
A famous mountain name is partly a height claim and partly a supply claim, and the two are not separable.
Tree age confounds it, since old trees on high ground are doing at least two things at once.
Processing overrides it, and a badly run wo dui ruins high grown leaf as easily as low grown leaf.
Storage overrides it more, and a decade in a damp room will spoil anything from any altitude.
Fake mountain names are the biggest limit of all, and they are common at every price level.
Bingdao and Yiwu sell far more tea than those areas produce, and most of it was grown somewhere else.
A printed altitude on a pu-erh cake carries no verification, and there is no register to check it against.
Blending is standard, so even an honest figure would describe an average rather than a garden.
Elevation stops helping near the top, where cold and thin soil produce a weak rather than a dense leaf.
Above roughly 2,000 m the material for long ageing is simply not there.
What can be checked is the maker, the storage and the price, and all three matter more.
Practical takeaway
Use altitude as background information and buy on maker and storage instead.
Learn the three technologies before you worry about any garden, since they separate the category more sharply.
Then learn factory tea before garden tea, because the price gap between them is smaller than the risk gap.
Only then is it worth asking how high a garden sits, and only from a seller who will name it.
Brew 5 grams in a 100 ml vessel at about 95 °C, after rinsing compressed leaf once.
Steep the first real infusion for 30 seconds and extend the time as the cake opens.
Judge a young raw cake on whether its bitterness turns sweet, which is the sign of material in the leaf.
A tea that stays flat and astringent came from thin leaf, whatever height is printed on the wrapper.
Run each sample to the 6th infusion, since dark tea reveals itself late in the session.
For Anhua and Liubao, skip altitude altogether and learn the bloom and the basket instead.
Check that a fu brick smells clean and earthy, and that a Liubao smells woody rather than musty.
Height sets the ceiling on what a dark tea can become, and storage decides whether it gets there.