It can be confusing – sometimes it’s called “pine bark”, sometimes “fir bark” or even “orchid bark”. Most people use the terms interchangeably, but their differences are quite significant especially when it comes to potting up your orchids, bonsai, and other houseplants.
What exactly are the differences?
Fir bark is a better growing substrate than pine bark, especially for potting orchids, bonsai or other houseplants because it is more resistant to decomposition and can thus last longer. It is less acidic when it is fresh. And it is more easily accessible and cheaper because it is locally sourced in the USA.
To learn about the 8 major differences between fir bark and pine bark as a growing medium, read on.
|Fir bark||Pine bark|
|Species||Douglas fir (Pseudotsuga menziesii)||Monterey pine (Pinus radiata)|
|Appearance||Rounded shape||Flat shape|
|Hardness||Hard, even when aged (last longer)||Crumbles at finger pressure when aged|
(last a shorter time)
|Water retention||Less water-retentive||More water absorbent and retentive|
|pH||Fresh bark less acidic (4.4 – 4.7) Aged fir bark acidic (3.5)||More acidic (3.4 – 4.8)|
|Nutrient content||Has recommended levels of P, K, Fe, Cu, Mn and micronutrients||Has lower levels of P|
|Accessibility||Cheaper, sourced locally in the USA, Canada||More expensive, imported from New Zealand|
|Sustainability||Highly sustainable||Highly sustainable|
Douglas Fir Bark (4qt bag)
1. What is “orchid bark”?
First of all, what is commonly known as “orchid bark” is not the bark of orchids – orchids do not have bark. It is the bark growing substrate used for orchids and is often fir bark or pine bark, or a mix of the two.
Fresh bark is sold soon after it is harvested from the tree, ground into smaller sizes, and screened.
“Orchid bark” is used as a growing substrate for orchids but also other houseplants, and even bonsai. It is also used as mulch for outdoor gardens.
2. Fir bark vs Pine bark
2.1 Classification and origins
Both fir and pine trees are evergreen conifers (i.e. cone-bearing). Although they come from the same plant family, Pinaceae, they belong to a different genus.
The “orchid bark” commonly sold and used in the orchid world is “Radiata Orchid bark”, which is pine bark from Pinus radiata or the Monterrey Pine from New Zealand. But, more and more people are now seeking out fir bark for potting up their orchids.
The “fir bark” sold on market is generally harvested from the dense outer layer of Douglas fir (Pseudotsuga menziesii), a native to the coastal forests of the Pacific Northwest. Although it is classified as one of the 40 plus existing fir species, many people say that Douglas fir is not a real fir because it has different characteristics than other fir trees.
Fir bark and pine bark have quite different shapes.
Some people prefer using fir bark as the growing substrate because it has a more rounded shape with its curls on the sides, making it more capable of holding water with less space in between. Pine bark, on the other hand, is flatter in shape.
2.3 Hardness and decomposition
Although Douglas fir is classified as softwood like all firs, its bark is very hard. In fact, it is even more durable than pine bark.
Their difference in hardness is even more obvious when the bark becomes aged. Although new pine bark fresh from the bag is quite hard, aged pine bark crumbles easily with finger pressure.
On the other hand, Douglas fir bark is more resistant to aging and still remains hard when aged.
2.4 Water absorption and retention
Pine bark absorbs water quickly even though it is fresh, while fir bark that is new from the bag sheds it. It takes longer for fir bark to absorb water.
2.5 Soil acidity
Both pine bark and fir bark are very acidic, with fresh fir bark less acidic than pine bark.
Pine has a pH of around 3.4 to 4.8 (Tucker 1995).
The pH of fir bark is 4.4 to 4.7 for fresh fir bark, and 3 to 3.5 for aged fir bark. (Buamscha & Altland, 2008).
Even if you soak bark in water for 24 hours, it can bring down the pH of the water from 8.65 to 5.88 to 6.27 (See this experiment for more details).
Therefore, if you want to acidify a soil mix for acid-loving plants such as orchids, mixing in pine bark is a sustainable practice.
2.6 Nutrient content
According to the US Department of Agriculture (Buamscha & Altland, 2008), fir bark contains exceptional amounts of phosphorus than pine wood bar.
Fir bark also contains amounts of potassium, iron, copper and manganese and also micronutrients within or above the levels recommended for growing container crops, except Calcium, Magnesium and Sulphate.
Since Radiata Orchid Bark is harvested from pines in New Zealand, it is more expensive and less accessible than fir bark which is locally sourced in the USA.
Fir trees are sustainable because they are huge storage for carbon and they reproduce quickly. Also, it can be locally sourced in the USA, Canada, and Europe, thus reducing the costs of transportation.
Yellow pine trees are also highly sustainable for similar reasons, except that it may be produced and imported from New Zealand.
3. Which is better for potting: fir bark vs pine bark?
Both fir bark and pine bark are acidic, aerate the soil, and hold up well for at least a year. Fir bark comes out as a better choice than pine bark because it is cheaper and locally sourced in the USA.
In particular, fir bark is a superior choice especially for plants such as orchids that require much ventilation between the roots and a growing substrate that is resistant to decomposition.
In orchid culture, it takes fir bark 2 years to decompose enough before it needs to be replaced with fresh ones. A growing substrate with pine bark would require replacement more quickly.
Fir bark is also a better growing substrate for bonsai also because of its higher durability. Although it would require 6 months to age or become “composted” prior use, the composted pieces can last for 4 years before turning into fine particles accumulated at the bottom of the pot.
4. What plants use fir bark?
Epiphytes that mostly thrive under acidic conditions are the ones that greatly benefit from fir bark especially when it is used as a standalone substrate. Plants that need to use fir bark include epiphytic orchids, moss, and certain types of fern.
Bonsai is another example of a plant that uses fir bark. While other barks such as cypress and cedar can be used for bonsai trees, experts do not recommend them based on the fact that they decay at a much slower rate. This means that they would subsequently not be able to offer sufficient nourishment for the bonsai tree.
5. Should you use fine or chunky bark?
Both fir and pine bark are available in fine, medium, and coarse grades. Bark with a small and medium particle size can absorb and hold much more water than larger ones.
As shown in an experiment, small-sized and medium-sized bark can absorb 47% and 43% of its dry weight respectively while large-sized bark can only absorb 27% of its dry weight.
For plants such as epiphytic orchids that are more susceptible to root rot and require more ventilation in between the roots, bark in medium to coarse grades is more suitable.
Bark in finer grade is suitable for general houseplants and bonsai.
Depending on the needs of the plant, fir bark is a better growing substrate than pine bark for plants that need much ventilation in between the roots because it takes longer to break down, retains less water. Also, it is cheaper and locally sourced in the USA.
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Bonsai Jack. Pine bark.
Bonsai Jack. Douglas Fir bark.
Buamscha, M. G. & Altland, J. E. (2008). What’s in your douglas-fir bark? USDA Forest Service Proceedings. US Department of Agriculture.
Tucker, M. R. (1995). Chemical characteristics for pine bark. Media notes for North Carolina growers. (accessed 3 March 2004). Raleigh (NC): North Carolina Department of Agriculture and Consumer Services.