There are two main ways to go with chemical-free sealants (and stain) for raised garden beds or planters.
The first option is to use a non-toxic water-based stain on the exterior with a safe water-based painted on membrane on the interior of the box. (The water-based stains used on the exterior won’t hold up inside the bed).
The second option is the most food-safe option, which is to use a totally natural penetrating oil on the inside and outside of the garden bed or container garden.
Some of these are only wood stains/sealants and some can be used on concrete and plastic planter boxes as well.
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1. Non-Toxic Stain & Sealant
Vermont Natural Coatings PolyWhey is a stain and sealant for the exterior of raised garden beds.
This is one of the most durable water-based (non-toxic) wood stain/sealers out there. This is a semi-transparent stain and sealer in one. It is a waterproofer that has some UV resistance (you get more UV resistance the darker you go with the stain color).
It can be used on new wood, pressure-treated wood, and weathered wood. Pressure-treated wood needs 6 months to a year to fully dry before this (or any) sealant is applied. It’s not for use on exotic super dense woods.
It could be applied over older oil-based stains or finishes, as well as water-based finishes if it’s been fully sanded first so that it can penetrate into the wood. No product can go over top of this in exterior applications.
This sealant is non-toxic, low odor, and low-VOC, and does not contain biocides, fungicides, or anti-microbial agents. The pigments act as natural UV inhibitors.
This coating is great for the exterior of raised garden beds with AFM Dynoseal for waterproofing on the interior.
2. Non-Toxic Invisible Waterproofer
Vermont Natural Coatings Penetrating Waterproofer with Juniper is an invisible-looking option for the exterior of raised planters.
This is another water-based sealant. This is a penetrating sealer that does not form a film on the surface; therefore it leaves the wood looks totally bare after applying it.
This sealant provides waterproofing but it does not provide any UV or abrasion resistance. The wood will gray out naturally from UV exposure.
It is used on the exterior of planters, and like all water-based sealants and paints, it is not suitable for subterranean or submerged wood.
For the inside of the planter, you will need a product that can resist moisture and prevent rotting – use AFM Dynoseal for this purpose.
It can be used on new wood, weathered wood, as well as pressure-treated wood. For pressure-treated wood allow 6-12 months for drying out before applying this sealant. It can work on teak and other oily woods and it is a good choice for cedar, pine, spruce, and fir.
It cannot go over or under another product.
It is zero-VOC and contains no solvents, dyes, biocides, or fungicides.
3. A Non-Toxic Waterproofer for Inside the Beds
AFM DynoSeal is for the interior of garden beds.
For the interior of the bed, the most durable non-toxic coating is AFM SafeCoat Dynoseal.
You paint it on and when it’s dry it acts as a waterproofing membrane that prevents moisture intrusion from the soil into the wood (preventing rot) and it stops tannins or chemical treatments in the wood from leaching into the soil and getting to the plant’s roots.
You can use this on the inside of planters made of wood, plastic, or concrete. It’s not for use on the outside of the planters, it doesn’t hold up to UV light and doesn’t look great either.
The partial ingredient list is: Acrylic Copolymer Emulsion and Pigment Dispersion. It’s listed at 19 g/l VOCs.
On the exterior, you can use PolyWhey, Penetrating Sealer with Juniper (listed above), or tung oil, linseed oil, or paint (listed below).
4. All-Natural Tung Oil Sealant
Outdoor Defense Oil is an all-natural tung, pine, and zinc mix that can be used for the interior and exterior of planters.
Pure tung oil is an all-natural product. The brand I use contains no synthetic, metallic, or other harmful additives.
It is non-toxic, and safe to use on organic garden structures that have contact with food supplies, including raised garden beds, chicken coops, and greenhouses.
Tung oil is very durable for a natural oil. It’s by far the most durable of the natural penetrating oils which is why it can be used on the inside as well as the outside of the garden bed. It seals moisture out of wood and its elastic properties help it hold up to movement and temperature changes. It’s very durable to mold.
Outdoor Defense Oil is an all-natural oil sealer made from pure tung oil, pine oil, and zinc.
You can also use this over Milk Paint to protect it from the elements or you can mix (some types of) pigments into the tung oil.
You can use this on all wood types. Extremely dense woods such as teak and ipe, etc may require thinning with more (natural) solvent. Because it needs to penetrate the wood it does not go over new oil-based sealers/stains or other finishes. You can use it over aged penetrating oil finishes (like aged linseed oil).
Some highly chemically sensitive folks have preferred these natural oil coatings to synthetic coatings like PolyWhey (others would find the opposite preferable).
Always test for your own tolerance and I would recommend not using or being exposed to the natural solvents used with tung oil (pine oil or citrus oil) when they are wet if you are sensitive.
Buy it through the Real Milk Company. You can use code mychemicalfreehouse for 10% off.
PS. To clean tung oiled wood, you can use gentle soaps, but some non-toxic cleaners can damage it – this post goes over the best options.
PPS. My in-depth look at tung and linseed oils goes into more detail on what these oils offgas.
5. Linseed Oil Stain & Sealant
Rubio Monocoat linseed-based stain & sealer can be used on the exterior of planters.
Rubio Monocoat Hybrid Wood Protector is a modified linseed oil and wax penetrating oil finish that is applied with just one coat.
This product is for exterior use, it provides protection from water and UV (except for the color “Pure” which has no UV protection).
It works well over almost all wood types including oily exotic woods (ipe, teak, etc).
It is solvent-free, technically zero-VOC because it’s a natural product. (Though see my in-depth review of Rubio Monocoat and other linseed oils for information on naturally occurring VOCs).
Rubio Monocoat is preferred to plain linseed oil in many ways because it’s lower in odor than the other brands. You need a part B accelerator, be sure to test that out as well.
You can buy it directly through their website.
6. Non-Toxic Paints
AFM or ECOS non-toxic paints can be used on the exterior of raised garden beds.
If you have older planters start by sanding off any rough areas or peeling paint and then prime the surface with AFM SafeCoat Transitional Primer. Next, paint the surface with AFM Safecoat Exterior Satin Paint.
Painting ultimately gives you the best protection against UV damage and other natural elements.
If you go with the painted option, you can’t use any penetrating sealant or oil-based stain and sealer over or under the painted surface.
If you prefer ECOS Paint brand you can use their exterior paints and primers.
What I wouldn’t use:
- “Teak oil” – any mix that contains tung and/or linseed with unknown ingredients or metallic driers would not be safe on the interior side next to the growing food.
- Linseed oil on the interior of the planter beds/container garden. It’s just not durable enough to hold up in here.
- Hemp oil or walnut oil – while you can use these two other penetrating drying oils on the exterior side they are not nearly as durable as linseed or tung oil. I would not be keen to use these outdoors.
- Jojoba oil – this is not a drying oil, it’s not a good finish for exterior wood.
- Milk Paint without a super durable top coat is not going to hold up outside.
Corinne Segura is a Building Biologist Practitioner with 7 years of experience helping others create healthy homes.
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