Trimming a candle wick is such a small difference that it seems like it shouldn’t affect using your candle too much. After all, your candle will still burn whether or not you trim the wick, right? While this is technically true, the small action of trimming the wick can help prolong the life of your candle by as much as 25% and keep it looking nice.
Leaving a wick long means that you’ll have a larger flame, which will melt more wax and give the candle more fuel. This larger amount of fuel can lead to incomplete combustion, which in turn creates more soot, making your candle container black and dirty. Many long wicks also form a little curl on top as they burn, creating an uneven shape that tends to waver around, which exacerbates the soot formation.
Keeping the candle wick trimmed helps control the amount of melted wax (i.e., fuel) that the candle has access to, which helps limit the amount of soot it creates. The trimmed wick also helps the candle burn more evenly, controlling the soot and prolonging the life of the candle. (Reducing the soot also makes it easier to repurpose the candle jar when you’re done burning the candle.)
Every time you burn a candle for four hours, extinguish the flame and let the candle cool to room temperature. This usually takes about two hours for larger candles. Then, trim the candle wick down to one-eighth to one-fourth inch before relighting again. You can use scissors at the beginning, but as the candle burns down it will be easier to use nail clippers or even an official wick trimmer.