Blue gum (Eucalyptus globulus) is called such because of the beautiful blue flowers that prominently bloom amongst its leave. These flowers carry a lot of pollen and are highly important for bees, though mostly in South Africa where they naturally grow.
Classed as an invasive species in some countries, blue gum is often only used for ornamental purposes. Even then, the tree has to be closely monitored.
If you do come across the rare blue gum in the US, is it worth using as firewood?
Blue gum is considered one of the best firewoods in the world but is not widely used in the US as it is not as common as other hardwoods. If you do come across blue gum, then it will make great firewood with one of the highest heat outputs of any wood.
What Are The Varieties Of Blue Gum
As a variety of eucalyptus itself, blue gum does not have any noticeable varieties. It does have a few in South Africa and Australia, but the tree is too rare to have a range of varieties in the US.
What Are The Physical Characteristics Of Blue Gum
| Name | Blue Gum |
| Heat per cord (Million BTUs) | 34.5 |
| Weight dry (lbs per cord) | |
| Weight green (lbs per cord) | |
| Seasoning time | 2 years |
| Resin / Sap content | Little |
| Splitting Difficulty | Difficult |
| Smoke | Minimal |
| Smell | Minty |
| Coal Production | Very good |
| Creosote Build-up | Little |
Does its Wood Split Easily?
You will need to split blue gum while it is still green as it will become extremely dense once seasoned.
Even when green, it can be difficult to split. Partly due to the wood’s natural density but also the twisted pattern that blue gum likes to grow, making it harder to find a good splitting point.
As the wood tends to produce a fair amount of oil, you will want to wear clothes you don’t mind getting dirty when splitting blue gum.
How Much Sap Does It Have?
Blue gum does not produce a lot of sap. Instead, it has a higher moisture and oil content than other trees producing more sap, such as pine.
How Does The Wood Smell?
How much you like the smell of blue gum will entirely depend on how you feel about the smell of mint.
Though blue gum does not smell distinctly of mint, it does have a strong fresh smell that is reminiscent of it.
Heat Output And Efficiency Of Blue Gum
Blue gum has one of the best heat outputs of any tree, with a very impressive BTU of 34.5. The main reason that it is not often included on BTU charts in the US is because of its rarity.
It is not a common enough species in the US to be of note to researchers and cataloguers. But if you do get your hands on some blue gum then you will get a substantial amount of heat from it.
Fire Characteristics Of Blue Gum
As an extremely dense wood, blue gum may take a while to ignite properly but once it does, it will burn very hot for a long time. To light a fire, you can use alder as kindling for example, or mix blue gum with hickory firewood.
Not only is the wood dense, but it also produces very good coals that will hold their heat even once the wood has burnt out. These will help to keep the fire burning for a longer time and will also help to restart another fire.
Even though blue gum does tend to hold its oils and moisture, it does dry out fairly well. So much so that it will not produce any smoke and will cause little creosote build-up.
Oil tends to be difficult to dry out in wood and often remains even once the wood has finished seasoning.
Blue gum is the same, but it burns hot enough to destroy the organic compounds in oils, meaning that they will not cling to your chimney and create a build-up of creosote.
Is It Okay To Burn Blue Gum In A Fireplace?
There is no doubting the phenomenal heat output of blue gum, but this heat can become too hot and overwhelming in a fireplace.
It is a safe wood to burn, creating minimal sparks and very little smoke. But you will want to mix blue gum in with cooler burning firewood to prevent its heat from becoming too much in your fireplace.
Burning blue gum in a log burner or at the very least an enclosed fireplace will also help to control its heat.
How Long To Season Blue Gum
Due to its higher than average moisture content and oil, blue gum will need at least 2 years to fully season.
This is also because the wood is so dense it will need those 2 years to reach a moisture content of less than 20% all of the way through the wood.
Pros And Cons of Blue Gum Wood
Pros
- Very efficient heat output
- Good coals
- Long burning time
- Minimal smoke
Cons
- Can be too hot
- Difficult to process
- Debatable smell
How Does Blue Gum Compare To Other Firewood?
Compared to other eucalyptus woods, blue gum burns better and hotter, resulting in less creosote build-up.
However, it can burn too hot and is not as common in the US as other hardwoods such as oak or hickory. That is why they are the preferred firewoods.
The smell of blue gum, while debatably pleasant, will not be overwhelming like the smell of sugar maple can be.
Frequently Asked Questions:
Is Blue Gum Sustainable?
Because blue gum is an invasive species in most areas of the world, it is often best to chop it down and use it as firewood to prevent it from spreading. This makes it a more sustainable wood than other hardwoods.
What Can I Mix With Blue Gum To Stop It From Burning Too Hot?
Softwoods like fir or cedar can help to lower the heat of blue gum and can help to get the fire going quicker. Though they also come with their own burning problems. A better option would be to mix it with alder or birch firewood.
Conclusion
Blue gum is a solid choice of firewood, presenting very few burning problems. Your main issue will be ensuring that its flames do not become too hot and overwhelming.
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I am the guy behind Theyardable.com. I grew up on a homestead and I am here to share the knowledge I have and things I learn while living in the countryside.
