The short answer is eight to twelve weeks. Ours are formulated to reach the top of that range.
The longer answer is that the spread between eight and twelve weeks is almost entirely down to things you control — and most people are unknowingly running their diffuser at the fast end.
What Actually Determines How Long It Lasts
How many reeds you use
This is the single biggest factor, and the one almost nobody adjusts. Every reed is a wick. Eight reeds draw oil roughly twice as fast as four.
Our diffusers come with eight reeds because that gives maximum fragrance throw in a large or open-plan room. But in a bedroom or a bathroom, eight reeds is often more fragrance than the space needs — you get a stronger scent for a shorter time, when you would probably have preferred the opposite.
If your diffuser is in a small room, start with four. You will likely find the scent level is perfectly good and the bottle lasts noticeably longer.
Heat
Fragrance oil evaporates faster when it is warm. A diffuser on a windowsill in direct sunlight, on a shelf above a radiator, or near a kitchen hob will run down considerably faster than one on a cool console table — and the fragrance itself can degrade, so the last few weeks smell weaker and less true.
This is the most common mistake we see. It is also the easiest to fix.
Airflow
Airflow is genuinely double-edged. Moving air is what carries fragrance through a room, so a diffuser in a sheltered corner will underperform no matter how many reeds are in it. But a diffuser sitting directly in a draught — beside a frequently opened front door, under an air vent — will evaporate quickly and throw most of its fragrance somewhere you are not.
What you want is gentle, natural air movement. Near a doorway rather than in the doorway.
Room size
A diffuser in a large open-plan space is doing more work than the same diffuser in a cloakroom. It will not necessarily empty faster — evaporation rate is driven mostly by reeds, heat and airflow — but you are more likely to add reeds to compensate, which does.
How to Make Yours Last Longer
- Use fewer reeds than you think you need. Start with four, live with it for a few days, add more only if you genuinely want more scent.
- Keep it out of direct sunlight and away from heat. Radiators, hobs, sunny windowsills and the top of a television all shorten a diffuser's life.
- Flip the reeds once a week, not daily. Flipping refreshes the scent, but every flip pushes saturated oil to the top where it evaporates faster. Weekly is the balance point.
- Do not top it up with anything. Adding water or oil of any kind changes the viscosity the formulation depends on and usually stops the reeds drawing properly.
My Diffuser Has Stopped Smelling of Anything
Before you assume it is finished, check the bottle. If there is still oil in it, one of three things is happening.
The reeds are saturated and clogged. Reeds gradually block with dust and thickened oil. Flipping them usually restores the throw immediately — try this first.
You have gone nose-blind to it. This is by far the most common explanation and it is not a fault. Your olfactory system stops registering a constant background scent within days. Leave the house for a few hours and walk back in; if you notice it on entry, the diffuser is working exactly as it should. Everyone visiting your home can still smell it.
It is genuinely spent. Once the oil is gone, it is gone — the reeds cannot draw what is not there.
When It Is Finished
Keep the bottle. Our vessels are 7cm round glass and are designed to be reused — refills are available across the range, so you replace the oil and reeds rather than the whole thing. It costs less and it is a great deal less wasteful. Get in touch and we will sort one out.
How Ours Are Built
Every William Alexander reed diffuser is hand poured in small batches in our Leicestershire studio, using a carefully balanced base designed to keep the fragrance throwing consistently from the first day to the last rather than peaking in week one and fading. Each comes with eight natural fibre reeds and arrives in a signature gift box, and UK delivery is free on every order.
More practical answers are on our FAQ page, or you can browse the full reed diffuser range.
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