Techniques to preserve wood when near or in contact with soil.
Authentic Pine Tar is created from cooking down resinous pine stumps. It has a long history of use in preserving and protecting exterior wood from deterioration. It was also the traditional and natural treatment to protect wood near or in contact with soil before modern pressure treated wood treatments.
As Authentic Pine Tar and Purified Linseed Oil combinations are gaining a renewed popularity for this specific application as folks are in search of healthier, more natural alternatives to petrochemical formulations, we are seeing more and more raised garden bed projects, fences and fence posts, log structures, etc.
Below are basic suggestions for raised garden bed projects or wood in a garden setting.
Principles also apply to other wood near or in contact with soil.
All Authentic Pine Tar options are non-toxic and can be used to saturate the wood substrate of the planter boxes/raised garden beds for flowers or veggies.
That said, the most traditional combination with the longest history of use is the Dark Pine Tar and Viking Purified Linseed Oil. This is a material that is basically the same since the Vikings used it to preserve and protect their sailing ships.
Dark Pine Tar has no additives and is simply a formulation of naturally occurring oils, resins, and terpenes from the pine stumps. In combination with the Viking Purified Linseed Oil, a naturally processed, food-grade flax oil, this is arguably the most natural and effective wood preservative on the planet. This is 100% petrochemical free and safe to use in the garden.
If a little pop of color is desired, the Pigmented Pine Tar options can also be used in the garden. These options, including Black, Black-Brown, Brown, and Red are formulated by the manufacturer with below 1% of additives to prevent a skin forming in the can and consequently not 100% petrochemical-free. These are far, far removed from modern complex-petrochemical coatings or wood preservatives in terms of health and safety.
So, it really comes down to your own personal values and what choices you want to make in your own garden.
Possible combinations:
Dark Pine Tar and Viking Purified Linseed Oil
The most traditional option and 100% petrochemical free. Color is going to range from a light to dark honey color on most wood substrates.
Pigmented Pine Tar and Viking Purified Linseed Oil
Offers some excellent color options: Black, Black-Brown, Brown, and Red. Not 100% petrochemical free.
Dark Pine Tar Mixture Inside and a Pigmented Pine Tar Outside
For the purists who also want some color.
Application Suggestions:
For a project that will come in contact with an excess amount of moisture inside and outside, possibly even direct contact with soil, really saturating the wood with the Pine Tar mixture will offer the best results. 1-2 coats of Pine Tar mixture will do something but it will not be as effective as multiple coats, especially in the case of surfaces in contact with soil.
This means the more work you put in on the front end, applying multiple coats inside and out, before installing into the soil, the longer life you can expect out of the wood.
Some slow and eventual deterioration is inevitable but the goal here is to slow this deterioration as much as possible. This is true for modern pressure treated timber as well.
Mix your Pine Tar and Viking Purified Linseed Oil to the ratio of choice. 50/50 is a common, effective ratio to consider. Mix well and mix well before each use.
Apply thin, even coats, allowing each coat to fully dry before applying the next.
The final coat, in theory, does not need to be fully dry before installation into the garden. Just avoid getting it onto clothes, etc. during install.
The Earth+Flax Raised Garden Bed Project used the Red Pine Tar 50/50 with the Viking Purified Linseed Oil.
Pine Tar Kits available with oil and a brush.