The four rules
Four rules cover almost everything: keep it cool, keep it dry, keep it dark, and keep it sealed. They apply to every tea, and they apply to oolong with one addition, which is separation by roast level.
Cool means below about 25 °C and steady. Dry means the tea itself stays dry, which is a question of packaging rather than of the room. Dark means out of light, and sealed means airtight rather than merely closed.
The addition is that oolong is not one material. A light, unroasted oolong behaves like a green tea and fades in months. A charcoal-roasted oolong behaves like a red tea and can sit for years without losing much.
So the first decision is not where to put the tea but which tea you have. Everything else follows from that, and the same cupboard will serve both cases as long as you do not mix them in one tin.
One number is worth carrying around: leaf above roughly 6 percent moisture can grow mould. Below that, with a seal in place, almost nothing will happen to a roasted oolong for 2 years.
Why each rule exists
Heat speeds up every chemical change in leaf, and oolong has more of those changes still available than green tea does. A roasted oolong held warm keeps slowly oxidising and slowly losing its roast character.
Moisture is the rule people break without noticing, because it arrives through the air rather than through a spill. Leaf takes up water from humid air, and once the leaf is above roughly 6 percent moisture, mould becomes possible.
Light breaks down the pigments and the aroma compounds near the surface, which is why a glass jar on a sunny shelf is the worst container in the house. It looks good and it costs you the tea.
Air is the fourth, and it does two things. Oxygen keeps the slow chemistry running, and any odour in the air will end up in the leaf. Oolong is less absorbent than green tea but it is not sealed against smell.
The rate matters more than the direction. A tea at 25 °C in a sealed tin changes slowly, while the same tea at 30 °C in a warm kitchen changes noticeably inside a single summer.
Apply it to Oolong tea
For a light oolong, treat it like green tea. Keep it sealed, keep it cool, and drink it within about 6 months of the roast or the packing date. A vacuum-sealed foil pouch in a cool cupboard does the job well.
For a roasted oolong, the goal changes. You want the roast to settle rather than to stay sharp, and that takes weeks rather than days. A sealed tin at room temperature is the right home, and it will improve for the first 3 months.
For an aged oolong, you want slow change rather than no change. Keep it sealed and dark, keep it away from strong smells, and accept that the tea will move a little every year. That movement is the point.
Separation matters because roast travels. A roasted oolong in the same tin as a light one will give the light one a roasted edge within a month, and there is no way to undo that.
A useful rule for quantity: 100 g of light oolong is about a month of daily drinking for one person, while a 100 g tin of roasted oolong can safely sit for a year without being touched.
Make it a habit
The habit that works is a rule about quantities rather than about containers. Buy oolong in amounts you will finish inside the window that suits that tea, and the storage problem largely solves itself.
Keep one tin per roast level, and label it with the month you opened it. A note on the lid costs nothing and tells you more about what happened to a tea than any amount of memory.
Re-check the seal when you refill. Zip locks wear out, tin lids warp, and a container that held a seal two years ago may not hold one now. This is the most common slow failure in a home setup.
Finally, taste the tea before you blame the storage. If a roasted oolong tastes flat after a month in a sealed tin, the tea was probably flat when it arrived, and no container would have saved it.
Put the oldest tea at the front of the shelf and work through it first. Rotation is the only storage habit that costs nothing, and it prevents the situation where you find a forgotten tin 2 years later.