Why Does My Wick Mushroom, and Is It a Problem?

A mushroom is a small ball of carbon that grows on the wick tip as the candle burns. Lone Star Candle Supply says it builds when the wick is feeding more fuel than the flame can fully burn. A little is common. A big one that bends over, drops into the wax or comes with soot is a sign to trim the wick and, if it keeps happening, size down. Test in your own jar with your own wick and wax, and never leave a burning candle unattended.

What should I do when I see one?

1. Put the flame out. The National Candle Association (NCA) suggests a snuffer or a gentle breath. It warns against water, which can make hot wax splatter.
2. Let the candle cool completely. Do not trim a wick that is lit or hot.
3. Trim the wick to 1/4 inch (6 mm). The NCA and CandleScience both say to do this before every burn.
4. Light it again and watch. If the mushroom comes back large, or the flame is tall or sooty, stop and test the next wick size down.

Why does a wick mushroom?

The suppliers I read list the same few causes.

• The wick itself. CandleScience says most mushrooming is simply a result of the wick's construction, and that it is normal with CD and ECO wicks. See our guide on CD, ECO, HTP and LX wicks.
• A wick that is too big. CandleScience says an over-wicked candle produces excess carbon that causes the mushrooming you see on the end of the wick.
• Too much fragrance or dye. Lone Star lists a heavy fragrance and dye load as a cause. CandleScience's soy guide says the same, and advises using less fragrance or dye.
• An untrimmed wick. CandleScience says mushrooming is much more dramatic if the wick is not trimmed to 1/4 inch (6 mm).
• A long burn. The NCA says burning too long builds carbon until the wick mushrooms. Lone Star lists a candle left to burn too long as a cause too.

Is a mushroom dangerous?

I did not find a source that calls a small mushroom dangerous. I did find two warnings about a big one. CandleScience says large mushrooming that tips the wick into the wax or drops carbon into the melt pool is a reason to wick down. The NCA says a mushroomed wick becomes unstable and can produce a dangerously large flame. So a big mushroom is a reason to put the candle out, not to watch it grow. The NCA also says to never leave a burning candle unattended.

How do I tell a normal mushroom from one that needs a smaller wick?

Look at the whole candle, not just the tip. CandleScience says a properly wicked candle has a melt pool that reaches the container's edge and is about 1/2 inch (13 mm) deep at the 2 hour mark, and an over-wicked one is deeper than that. Its soy troubleshooting guide says to size down one wick size in the same series if the pool gets deeper than 1/2 inch within 30 minutes, with excess smoke or soot. The two pages use different time marks, so I would not pick one number for every jar. Judge a wick with the burn test you already use, and read our guide on wicks that are too big for the other signs.

Worked example: scoring mushrooms across a wick series

Three test candles share one jar, one wax and one fragrance load. Only the wick size changes: smaller, middle, larger. Stay with the candles, burn each for 2 hours, let it cool, and score the mushroom before trimming. The 0 to 3 scale is made up for this example: 0 none, 1 small, 2 large, 3 large and dropping carbon into the wax. Scores are examples.

The larger wick scored 3 on three burns running, so it is out. The middle wick sits at 2 and is worth a second look at its flame and jar heat. The smaller wick stays at 1, but check that its melt pool still reaches the edge. If the smaller wick's melt pool stops short of the edge, read the guide on wicks that are too small. Do not change the fragrance load in the same round, or you will not know which change did it.

What should I tell customers?

Put it on the care card: trim the wick to 1/4 inch before every burn, and do not burn longer than four hours at a time. The NCA's general advice is no more than four hours, then at least two hours to cool before relighting, and it says to follow the maker's instructions first. For your own tests, CandleScience's burn test page asks for at least five hours of cooling between burns, so the two numbers are for different jobs.

Common mistakes

• Trimming a hot or lit wick.
• Changing the wick and the fragrance load in the same test.
• Blaming the wick when the load is far above what the wax can hold.
• Letting a test run just to see how large the flame gets.
• Telling customers "trim as needed" without a length.

Questions

Can I pinch off the mushroom while the candle is burning?

I would not. Put the flame out, let it cool, and trim to 1/4 inch (6 mm), which is what CandleScience and the NCA both say to do before lighting.

Does a mushroom mean my fragrance load is too high?

It can. Lone Star and CandleScience both list heavy fragrance and dye as causes. Change one thing at a time and compare. Our guide on maximum fragrance load covers the limits.