Tea is more fragile than coffee but more forgiving than people think. Store it badly and a fine green tea will be flat in three months. Store it reasonably and most teas keep their character for a year or more. Some, notably aged pu-erh, actively improve with time. The differences come down to a few simple factors.
What ages tea badly
Air, light, heat, moisture, and strong smells. Oxygen oxidises the aromatic compounds. Light accelerates it, especially direct sun. Heat speeds the chemical changes that make tea stale. Moisture causes mould or fermentation. Strong smells (kitchen spices, perfume) are absorbed straight into the leaves.
The original packaging tea comes in is rarely a good long-term solution. Decant into something better as soon as you open it.
Good storage
An opaque container with an airtight lid in a cool dry cupboard. Tin canisters with rubber seals work well. Glass jars work too if kept in a dark cupboard but become a problem if left on a shelf in the light.
For everyday teas, a normal-sized container is fine. For special teas you will use over many months, smaller containers help — open the small one frequently, leave the bulk sealed and untouched. Each opening adds a little oxygen exposure.
Which teas keep best
Black tea and roasted oolong: most resilient. A year or more without noticeable decline if stored well.
Light oolong and white tea: moderate. Six months to a year of peak quality.
Green tea and yellow tea: fragile. Three to six months. Some Japanese green teas (gyokuro, sencha) noticeably degrade in weeks if stored badly. Buying small amounts often is better than stocking up.
Pu-erh: opposite. Sheng pu-erh is often aged for decades and the value goes up. Shou pu-erh is more stable and changes less. Both want some air circulation, the opposite of every other tea.
The fridge question
Some Japanese green teas benefit from refrigeration, particularly through summer heat — but only in airtight bags inside containers, and only opened after warming to room temperature to avoid condensation. For most teas this is unnecessary fuss. A cool dark cupboard is enough.