Natural, Food-Safe and Water-Resistant Finishes for your Wooden Raised Garden Planter Box and Raised Bed Garden
One of the questions we get asked a lot is whether our planters need to be coated with anything before planting. The short answer is that no, none of our planters require a coating and they should last several years even out in the elements. Our planters are made from a species of rot-resistant fir wood with the scientific name Cunninghamia Lanceolata. This species is also known as aromatic cedar or Asian cedar and, like all cedars, it will turn gray over time as it ages. However, if you want to try to preserve the color a little longer and potentially extend the life of your planter as well, you might want to consider adding a water-resistant finish.
We put together this post to help you understand the results you might get with a couple of different natural finishes compared with leaving your planter untreated. We used our heavy-duty tall log planters for this project, but you will get similar results with any of our planters as all of them use the same type of wood. Since we mostly use our planters to grow vegetables and herbs, we only wanted to test products that were food safe. We also wanted products that were easy to apply and not too expensive. In the end, we settled on testing Tung Oil and Shellac.
If you'd rather watch a video on this, we provided an overview of the finished products in a video:
The Bottom Line
If you don’t want to read the whole thing, here’s our preference after the first month: Shellac, but it’s not by a landslide so if you can only find Tung Oil, it will be just fine. Shellac went on easily, did not change the color as much as Tung Oil, and seemed to have better initial water resistance. It also did not leave any kind of oily residue but rather had a clear coat / polyurethane-type finish.
Left: Coated with Tung Oil Right: Coated with Shellac
Tung Oil is a natural oil that is extracted by pressing the nuts of the Tung Tree. We purchased a pint (16 oz) of Tung Oil on Amazon for about $20, though it can probably be found less expensively in a local store. One pint proved to be just enough for one heavy coating over all surfaces of one planter. The instructions on the bottle mentioned that we could thin the product with mineral spirits to provide better coverage, and that probably would have given us enough for additional coats, but one un-thinned coat seemed to provide adequate moisture resistance.
The first thing we did to get ready for the oil was to spread out the box that the planter arrives in. This proved to be the perfect canvas to use to apply the oil. We then laid out all the pieces and got out our foam brushes. The method we used was to pour the oil onto the panel a little at a time, and use the brushes to quickly spread it around. Because our panels use tongue-and-groove joints, the oil didn’t drip through the other side.
We thoroughly covered the side facing up and then flipped it over and repeated for the other side. This was a pretty easy process and there isn’t much to it, but I also had several young helpers to make it go more quickly.
As you can see, the oil is light in color, and it was easy to apply. Straight from the bottle it was slightly thicker and darker than canola oil. When covered in oil, the wood takes on a little more of a darker yellow color than the natural color of the wood. Having seen several of these planters weather and age, I can tell you that it looks a lot like it would look if it was left untreated and got wet, which is similar to the color that the wood takes on after weathering for a couple of weeks in the elements. The hope here is that it will hold this color for longer than the natural wood, which fades in the sun over the first several months and then slowly turns to gray over the following year.
The Tung Oil instructions said to wipe down the surface with a rag after an hour, but we just let the oil sit and ended up with great results. It did make our hands a little oily when handling the wood right after, but we let it sit for a few days before assembly and didn’t notice any oil getting on our hands when we finally assembled it. Of note, the oil seemed to make the wood a little softer when we assembled it than an unfinished planter would be. I don’t think it will affect the longevity at all, but we dialed back the torque setting on our electric drill a little to compensate for the change.
We splashed a little water on the planter to see how it handled it – you can see it beaded up well, but it did seem to soak into the surface a little bit. This is a promising start, but it remains to be seen how long this water resistance will last. We will follow up again after a few weeks to see how it’s holding up!
The other finish we used was Shellac. This natural resin is known to be food safe and is secreted by the shellac bug. Once again, we went with Amazon to get it delivered to our door, and a quart of Shellac cost about $15. One quart was plenty to cover all sides of the planter and even place a second coat on the inside portions and legs with a little left over.
Similar to the Tung Oil, we spread out some cardboard to act as a working area for applying the Shellac. We then laid out all the pieces and got out our foam brushes again. This time we found that the most effective way of applying the Shellac was to simply dip the brush in the shellac and brush it on the pieces. The consistency was a lot thinner than the Tung Oil, so it likely would have wasted quite a bit to pour it on. It was interesting to work with the Shellac as it dries a little like wax – if you don’t smooth it out it will be thicker in some spots than others. That wasn’t a problem, just an observation.
We started with the inside portions of the panels, applied a full coat to everything within about 45 minutes and then let it sit for another 20 minutes or so before applying a second coat to the inside parts and legs. The instructions said to sand with 220 grit sandpaper between coats, but we didn’t find that to be necessary for our purposes. Once everything was dry, we assembled it to get a better look at everything.
As you can see, the color turned out great. It’s still darker and more yellow than the unfinished version, but if you want a food-safe water-resistant coating on your planter then this is probably the closest you can get to the original color.
We splashed water on the Shellac-coated planter and it beaded up really well – in fact, it seemed like no water soaked into the wood at all. This result was noticeably better than the Tung Oil, but we’re not sure how long the coating will last.
Now let’s compare the two finished planters together.
Left: Coated with Tung Oil Right: Coated with Shellac
You can see that the Tung Oil is a little darker, but also pulls out the color of the knots in the wood a lot more. The logo on the Tung Oil planter is much darker, but this is a little misleading because it was much darker to begin with anyway.
For reference, Here's what our untreated planter looked like on day one this year:
We had planned to post ongoing updates but life seemed to get in the way and we weren't able to take photos in a timely manner. Here's our bottom line:
We would only recommend tung oil or shellac if you are willing to keep up with re-applying every couple of months during the season. If you don't re-apply, you will get patches of aged wood that grow over time.
Our family has found that leaving these planters natural is the easiest method and guarantees a uniformly aged product if it's going to be left fully in the elements. If you are keeping it under a cover (such as a patio roof), and only watering inside the planter, then you will probably have better results with some type of finish.
We have not found that coated / finished planters last significantly longer than raw wood -- while it's likely they will, the natural wood lasts for many years even the way it is.
For another option that we've had great results with so far, you might consider the "Vermont Naturals Juniper Infused" water sealant. We love the look and have been impressed with the way it weathers so far.
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